mkfs: symlink support

[minix.git] / drivers / ahci / ahci.c

/* Advanced Host Controller Interface (AHCI) driver, by D.C. van Moolenbroek
 * - Multithreading support by Arne Welzel
 * - Native Command Queuing support by Raja Appuswamy
 */
/*
 * This driver is based on the following specifications:
 * - Serial ATA Advanced Host Controller Interface (AHCI) 1.3
 * - Serial ATA Revision 2.6
 * - AT Attachment with Packet Interface 7 (ATA/ATAPI-7)
 * - ATAPI Removable Rewritable Media Devices 1.3 (SFF-8070)
 *
 * The driver supports device hot-plug, active device status tracking,
 * nonremovable ATA and removable ATAPI devices, custom logical sector sizes,
 * sector-unaligned reads, native command queuing and parallel requests to
 * different devices.
 *
 * It does not implement transparent failure recovery, power management, or
 * port multiplier support.
 */
/*
 * An AHCI controller exposes a number of ports (up to 32), each of which may
 * or may not have one device attached (port multipliers are not supported).
 * Each port is maintained independently.
 *
 * The following figure depicts the possible transitions between port states.
 * The NO_PORT state is not included; no transitions can be made from or to it.
 *
 *   +----------+                      +----------+
 *   | SPIN_UP  | ------+      +-----> | BAD_DEV  | ------------------+
 *   +----------+       |      |       +----------+                   |
 *        |             |      |            ^                         |
 *        v             v      |            |                         |
 *   +----------+     +----------+     +----------+     +----------+  |
 *   |  NO_DEV  | --> | WAIT_SIG | --> | WAIT_ID  | --> | GOOD_DEV |  |
 *   +----------+     +----------+     +----------+     +----------+  |
 *        ^                |                |                |        |
 *        +----------------+----------------+----------------+--------+
 *
 * At driver startup, all physically present ports are put in SPIN_UP state.
 * This state differs from NO_DEV in that BDEV_OPEN calls will be deferred
 * until either the spin-up timer expires, or a device has been identified on
 * that port. This prevents early BDEV_OPEN calls from failing erroneously at
 * startup time if the device has not yet been able to announce its presence.
 *
 * If a device is detected, either at startup time or after hot-plug, its
 * signature is checked and it is identified, after which it may be determined
 * to be a usable ("good") device, which means that the device is considered to
 * be in a working state. If these steps fail, the device is marked as unusable
 * ("bad"). At any point in time, the device may be disconnected; the port is
 * then put back into NO_DEV state.
 *
 * A device in working state (GOOD_DEV) may or may not have a medium. All ATA
 * devices are assumed to be fixed; all ATAPI devices are assumed to have
 * removable media. To prevent erroneous access to switched devices and media,
 * the driver makes devices inaccessible until they are fully closed (the open
 * count is zero) when a device (hot-plug) or medium change is detected.
 * For hot-plug changes, access is prevented by setting the BARRIER flag until
 * the device is fully closed and then reopened. For medium changes, access is
 * prevented by not acknowledging the medium change until the device is fully
 * closed and reopened. Removable media are not locked in the drive while
 * opened, because the driver author is uncomfortable with that concept.
 *
 * The following table lists for each state, whether the port is started
 * (PxCMD.ST is set), whether a timer is running, what the PxIE mask is to be
 * set to, and what BDEV_OPEN calls on this port should return.
 *
 *   State       Started     Timer       PxIE        BDEV_OPEN
 *   ---------   ---------   ---------   ---------   ---------
 *   NO_PORT     no          no          (none)      ENXIO
 *   SPIN_UP     no          yes         PRCE        (wait)
 *   NO_DEV      no          no          PRCE        ENXIO
 *   WAIT_SIG    yes         yes         PRCE        (wait)
 *   WAIT_ID     yes         yes         (all)       (wait)
 *   BAD_DEV     no          no          PRCE        ENXIO
 *   GOOD_DEV    yes         per-command (all)       OK
 *
 * In order to continue deferred BDEV_OPEN calls, the BUSY flag must be unset
 * when changing from SPIN_UP to any state but WAIT_SIG, and when changing from
 * WAIT_SIG to any state but WAIT_ID, and when changing from WAIT_ID to any
 * other state.
 */
/*
 * The maximum byte size of a single transfer (MAX_TRANSFER) is currently set
 * to 4MB. This limit has been chosen for a number of reasons:
 * - The size that can be specified in a Physical Region Descriptor (PRD) is
 *   limited to 4MB for AHCI. Limiting the total transfer size to at most this
 *   size implies that no I/O vector element needs to be split up across PRDs.
 *   This means that the maximum number of needed PRDs can be predetermined.
 * - The limit is below what can be transferred in a single ATA request, namely
 *   64k sectors (i.e., at least 32MB). This means that transfer requests need
 *   never be split up into smaller chunks, reducing implementation complexity.
 * - A single, static timeout can be used for transfers. Very large transfers
 *   can legitimately take up to several minutes -- well beyond the appropriate
 *   timeout range for small transfers. The limit obviates the need for a
 *   timeout scheme that takes into account the transfer size.
 * - Similarly, the transfer limit reduces the opportunity for buggy/malicious
 *   clients to keep the driver busy for a long time with a single request.
 * - The limit is high enough for all practical purposes. The transfer setup
 *   overhead is already relatively negligible at this size, and even larger
 *   requests will not help maximize throughput. As NR_IOREQS is currently set
 *   to 64, the limit still allows file systems to perform I/O requests with
 *   vectors completely filled with 64KB-blocks.
 */
#include <minix/drivers.h>
#include <minix/blockdriver_mt.h>
#include <minix/drvlib.h>
#include <machine/pci.h>
#include <sys/ioc_disk.h>
#include <sys/mman.h>
#include <assert.h>

#include "ahci.h"

/* Host Bus Adapter (HBA) state. */
static struct {
        volatile u32_t *base;   /* base address of memory-mapped registers */
        size_t size;            /* size of memory-mapped register area */

        int nr_ports;           /* addressable number of ports (1..NR_PORTS) */
        int nr_cmds;            /* maximum number of commands per port */
        int has_ncq;            /* NCQ support flag */

        int irq;                /* IRQ number */
        int hook_id;            /* IRQ hook ID */
} hba_state;

/* Port state. */
static struct port_state {
        int state;              /* port state */
        unsigned int flags;     /* port flags */

        volatile u32_t *reg;    /* memory-mapped port registers */

        u8_t *mem_base;         /* primary memory buffer virtual address */
        phys_bytes mem_phys;    /* primary memory buffer physical address */
        vir_bytes mem_size;     /* primary memory buffer size */

        /* the FIS, CL, CT[0] and TMP buffers are all in the primary buffer */
        u32_t *fis_base;        /* FIS receive buffer virtual address */
        phys_bytes fis_phys;    /* FIS receive buffer physical address */
        u32_t *cl_base;         /* command list buffer virtual address */
        phys_bytes cl_phys;     /* command list buffer physical address */
        u8_t *ct_base[NR_CMDS]; /* command table virtual address */
        phys_bytes ct_phys[NR_CMDS];    /* command table physical address */
        u8_t *tmp_base;         /* temporary storage buffer virtual address */
        phys_bytes tmp_phys;    /* temporary storage buffer physical address */

        u8_t *pad_base;         /* sector padding buffer virtual address */
        phys_bytes pad_phys;    /* sector padding buffer physical address */
        vir_bytes pad_size;     /* sector padding buffer size */

        u64_t lba_count;        /* number of valid Logical Block Addresses */
        u32_t sector_size;      /* medium sector size in bytes */

        int open_count;         /* number of times this port is opened */

        int device;             /* associated device number, or NO_DEVICE */
        struct device part[DEV_PER_DRIVE];      /* partition bases and sizes */
        struct device subpart[SUB_PER_DRIVE];   /* same for subpartitions */

        timer_t timer;          /* port-specific timeout timer */
        int left;               /* number of tries left before giving up */
                                /* (only used for signature probing) */

        int queue_depth;        /* NCQ queue depth */
        u32_t pend_mask;        /* commands not yet complete */
        struct {
                thread_id_t tid;/* ID of the worker thread */
                timer_t timer;  /* timer associated with each request */
                int result;     /* success/failure result of the commands */
        } cmd_info[NR_CMDS];
} port_state[NR_PORTS];

static int ahci_instance;                       /* driver instance number */

static int ahci_verbose;                        /* verbosity level (0..4) */

/* Timeout values. These can be overridden with environment variables. */
static long ahci_spinup_timeout = SPINUP_TIMEOUT;
static long ahci_sig_timeout = SIG_TIMEOUT;
static long ahci_sig_checks = NR_SIG_CHECKS;
static long ahci_command_timeout = COMMAND_TIMEOUT;
static long ahci_transfer_timeout = TRANSFER_TIMEOUT;
static long ahci_flush_timeout = FLUSH_TIMEOUT;

static int ahci_map[MAX_DRIVES];                /* device-to-port mapping */

static int ahci_exiting = FALSE;                /* exit after last close? */

#define BUILD_ARG(port, tag)    (((port) << 8) | (tag))
#define GET_PORT(arg)           ((arg) >> 8)
#define GET_TAG(arg)            ((arg) & 0xFF)

#define dprintf(v,s) do {               \
        if (ahci_verbose >= (v))        \
                printf s;               \
} while (0)

static void port_set_cmd(struct port_state *ps, int cmd, cmd_fis_t *fis,
        u8_t packet[ATAPI_PACKET_SIZE], prd_t *prdt, int nr_prds, int write);
static void port_issue(struct port_state *ps, int cmd, clock_t timeout);
static int port_exec(struct port_state *ps, int cmd, clock_t timeout);
static void port_timeout(struct timer *tp);
static void port_disconnect(struct port_state *ps);

static char *ahci_portname(struct port_state *ps);
static int ahci_open(dev_t minor, int access);
static int ahci_close(dev_t minor);
static ssize_t ahci_transfer(dev_t minor, int do_write, u64_t position,
        endpoint_t endpt, iovec_t *iovec, unsigned int count,
        int flags);
static struct device *ahci_part(dev_t minor);
static void ahci_alarm(clock_t stamp);
static int ahci_ioctl(dev_t minor, unsigned int request, endpoint_t endpt,
        cp_grant_id_t grant);
static void ahci_intr(unsigned int mask);
static int ahci_device(dev_t minor, device_id_t *id);
static struct port_state *ahci_get_port(dev_t minor);

/* AHCI driver table. */
static struct blockdriver ahci_dtab = {
        BLOCKDRIVER_TYPE_DISK,
        ahci_open,
        ahci_close,
        ahci_transfer,
        ahci_ioctl,
        NULL,           /* bdr_cleanup */
        ahci_part,
        NULL,           /* bdr_geometry */
        ahci_intr,
        ahci_alarm,
        NULL,           /* bdr_other */
        ahci_device
};

/*===========================================================================*
 *                              atapi_exec                                   *
 *===========================================================================*/
static int atapi_exec(struct port_state *ps, int cmd,
        u8_t packet[ATAPI_PACKET_SIZE], size_t size, int write)
{
        /* Execute an ATAPI command. Return OK or error.
         */
        cmd_fis_t fis;
        prd_t prd[1];
        int nr_prds = 0;

        assert(size <= AHCI_TMP_SIZE);

        /* Fill in the command table with a FIS, a packet, and if a data
         * transfer is requested, also a PRD.
         */
        memset(&fis, 0, sizeof(fis));
        fis.cf_cmd = ATA_CMD_PACKET;

        if (size > 0) {
                fis.cf_feat = ATA_FEAT_PACKET_DMA;
                if (!write && (ps->flags & FLAG_USE_DMADIR))
                        fis.cf_feat |= ATA_FEAT_PACKET_DMADIR;

                prd[0].vp_addr = ps->tmp_phys;
                prd[0].vp_size = size;
                nr_prds++;
        }

        /* Start the command, and wait for it to complete or fail. */
        port_set_cmd(ps, cmd, &fis, packet, prd, nr_prds, write);

        return port_exec(ps, cmd, ahci_command_timeout);
}

/*===========================================================================*
 *                              atapi_test_unit                              *
 *===========================================================================*/
static int atapi_test_unit(struct port_state *ps, int cmd)
{
        /* Test whether the ATAPI device and medium are ready.
         */
        u8_t packet[ATAPI_PACKET_SIZE];

        memset(packet, 0, sizeof(packet));
        packet[0] = ATAPI_CMD_TEST_UNIT;

        return atapi_exec(ps, cmd, packet, 0, FALSE);
}

/*===========================================================================*
 *                              atapi_request_sense                          *
 *===========================================================================*/
static int atapi_request_sense(struct port_state *ps, int cmd, int *sense)
{
        /* Request error (sense) information from an ATAPI device, and return
         * the sense key. The additional sense codes are not used at this time.
         */
        u8_t packet[ATAPI_PACKET_SIZE];
        int r;

        memset(packet, 0, sizeof(packet));
        packet[0] = ATAPI_CMD_REQUEST_SENSE;
        packet[4] = ATAPI_REQUEST_SENSE_LEN;

        r = atapi_exec(ps, cmd, packet, ATAPI_REQUEST_SENSE_LEN, FALSE);

        if (r != OK)
                return r;

        dprintf(V_REQ, ("%s: ATAPI SENSE: sense %x ASC %x ASCQ %x\n",
                ahci_portname(ps), ps->tmp_base[2] & 0xF, ps->tmp_base[12],
                ps->tmp_base[13]));

        *sense = ps->tmp_base[2] & 0xF;

        return OK;
}

/*===========================================================================*
 *                              atapi_load_eject                             *
 *===========================================================================*/
static int atapi_load_eject(struct port_state *ps, int cmd, int load)
{
        /* Load or eject a medium in an ATAPI device.
         */
        u8_t packet[ATAPI_PACKET_SIZE];

        memset(packet, 0, sizeof(packet));
        packet[0] = ATAPI_CMD_START_STOP;
        packet[4] = load ? ATAPI_START_STOP_LOAD : ATAPI_START_STOP_EJECT;

        return atapi_exec(ps, cmd, packet, 0, FALSE);
}

/*===========================================================================*
 *                              atapi_read_capacity                          *
 *===========================================================================*/
static int atapi_read_capacity(struct port_state *ps, int cmd)
{
        /* Retrieve the LBA count and sector size of an ATAPI medium.
         */
        u8_t packet[ATAPI_PACKET_SIZE], *buf;
        int r;

        memset(packet, 0, sizeof(packet));
        packet[0] = ATAPI_CMD_READ_CAPACITY;

        r = atapi_exec(ps, cmd, packet, ATAPI_READ_CAPACITY_LEN, FALSE);
        if (r != OK)
                return r;

        /* Store the number of LBA blocks and sector size. */
        buf = ps->tmp_base;
        ps->lba_count = add64u(cvu64((buf[0] << 24) | (buf[1] << 16) |
                (buf[2] << 8) | buf[3]), 1);
        ps->sector_size =
                (buf[4] << 24) | (buf[5] << 16) | (buf[6] << 8) | buf[7];

        if (ps->sector_size == 0 || (ps->sector_size & 1)) {
                dprintf(V_ERR, ("%s: invalid medium sector size %u\n",
                        ahci_portname(ps), ps->sector_size));

                return EINVAL;
        }

        dprintf(V_INFO,
                ("%s: medium detected (%u byte sectors, %lu MB size)\n",
                ahci_portname(ps), ps->sector_size,
                div64u(mul64(ps->lba_count, cvu64(ps->sector_size)),
                1024*1024)));

        return OK;
}

/*===========================================================================*
 *                              atapi_check_medium                           *
 *===========================================================================*/
static int atapi_check_medium(struct port_state *ps, int cmd)
{
        /* Check whether a medium is present in a removable-media ATAPI device.
         * If a new medium is detected, get its total and sector size. Return
         * OK only if a usable medium is present, and an error otherwise.
         */
        int sense;

        /* Perform a readiness check. */
        if (atapi_test_unit(ps, cmd) != OK) {
                ps->flags &= ~FLAG_HAS_MEDIUM;

                /* If the check failed due to a unit attention condition, retry
                 * reading the medium capacity. Otherwise, assume that there is
                 * no medium available.
                 */
                if (atapi_request_sense(ps, cmd, &sense) != OK ||
                                sense != ATAPI_SENSE_UNIT_ATT)
                        return ENXIO;
        }

        /* If a medium is newly detected, try reading its capacity now. */
        if (!(ps->flags & FLAG_HAS_MEDIUM)) {
                if (atapi_read_capacity(ps, cmd) != OK)
                        return EIO;

                ps->flags |= FLAG_HAS_MEDIUM;
        }

        return OK;
}

/*===========================================================================*
 *                              atapi_id_check                               *
 *===========================================================================*/
static int atapi_id_check(struct port_state *ps, u16_t *buf)
{
        /* Determine whether we support this ATAPI device based on the
         * identification data it returned, and store some of its properties.
         */

        /* The device must be an ATAPI device; it must have removable media;
         * it must support DMA without DMADIR, or DMADIR for DMA.
         */
        if ((buf[ATA_ID_GCAP] & (ATA_ID_GCAP_ATAPI_MASK |
                ATA_ID_GCAP_REMOVABLE | ATA_ID_GCAP_INCOMPLETE)) !=
                (ATA_ID_GCAP_ATAPI | ATA_ID_GCAP_REMOVABLE) ||
                ((buf[ATA_ID_CAP] & ATA_ID_CAP_DMA) != ATA_ID_CAP_DMA &&
                (buf[ATA_ID_DMADIR] & (ATA_ID_DMADIR_DMADIR |
                ATA_ID_DMADIR_DMA)) != (ATA_ID_DMADIR_DMADIR |
                ATA_ID_DMADIR_DMA))) {

                dprintf(V_ERR, ("%s: unsupported ATAPI device\n",
                        ahci_portname(ps)));

                dprintf(V_DEV, ("%s: GCAP %04x CAP %04x DMADIR %04x\n",
                        ahci_portname(ps), buf[ATA_ID_GCAP], buf[ATA_ID_CAP],
                        buf[ATA_ID_DMADIR]));

                return FALSE;
        }

        /* Remember whether to use the DMADIR flag when appropriate. */
        if (buf[ATA_ID_DMADIR] & ATA_ID_DMADIR_DMADIR)
                ps->flags |= FLAG_USE_DMADIR;

        /* ATAPI CD-ROM devices are considered read-only. */
        if (((buf[ATA_ID_GCAP] & ATA_ID_GCAP_TYPE_MASK) >>
                ATA_ID_GCAP_TYPE_SHIFT) == ATAPI_TYPE_CDROM)
                ps->flags |= FLAG_READONLY;

        if ((buf[ATA_ID_SUP1] & ATA_ID_SUP1_VALID_MASK) == ATA_ID_SUP1_VALID &&
                !(ps->flags & FLAG_READONLY)) {
                /* Save write cache related capabilities of the device. It is
                 * possible, although unlikely, that a device has support for
                 * either of these but not both.
                 */
                if (buf[ATA_ID_SUP0] & ATA_ID_SUP0_WCACHE)
                        ps->flags |= FLAG_HAS_WCACHE;

                if (buf[ATA_ID_SUP1] & ATA_ID_SUP1_FLUSH)
                        ps->flags |= FLAG_HAS_FLUSH;
        }

        return TRUE;
}

/*===========================================================================*
 *                              atapi_transfer                               *
 *===========================================================================*/
static int atapi_transfer(struct port_state *ps, int cmd, u64_t start_lba,
        unsigned int count, int write, prd_t *prdt, int nr_prds)
{
        /* Perform data transfer from or to an ATAPI device.
         */
        cmd_fis_t fis;
        u8_t packet[ATAPI_PACKET_SIZE];

        /* Fill in a Register Host to Device FIS. */
        memset(&fis, 0, sizeof(fis));
        fis.cf_cmd = ATA_CMD_PACKET;
        fis.cf_feat = ATA_FEAT_PACKET_DMA;
        if (!write && (ps->flags & FLAG_USE_DMADIR))
                fis.cf_feat |= ATA_FEAT_PACKET_DMADIR;

        /* Fill in a packet. */
        memset(packet, 0, sizeof(packet));
        packet[0] = write ? ATAPI_CMD_WRITE : ATAPI_CMD_READ;
        packet[2] = (ex64lo(start_lba) >> 24) & 0xFF;
        packet[3] = (ex64lo(start_lba) >> 16) & 0xFF;
        packet[4] = (ex64lo(start_lba) >>  8) & 0xFF;
        packet[5] = ex64lo(start_lba) & 0xFF;
        packet[6] = (count >> 24) & 0xFF;
        packet[7] = (count >> 16) & 0xFF;
        packet[8] = (count >>  8) & 0xFF;
        packet[9] = count & 0xFF;

        /* Start the command, and wait for it to complete or fail. */
        port_set_cmd(ps, cmd, &fis, packet, prdt, nr_prds, write);

        return port_exec(ps, cmd, ahci_transfer_timeout);
}

/*===========================================================================*
 *                              ata_id_check                                 *
 *===========================================================================*/
static int ata_id_check(struct port_state *ps, u16_t *buf)
{
        /* Determine whether we support this ATA device based on the
         * identification data it returned, and store some of its properties.
         */

        /* This must be an ATA device; it must not have removable media;
         * it must support LBA and DMA; it must support the FLUSH CACHE
         * command; it must support 48-bit addressing.
         */
        if ((buf[ATA_ID_GCAP] & (ATA_ID_GCAP_ATA_MASK | ATA_ID_GCAP_REMOVABLE |
                ATA_ID_GCAP_INCOMPLETE)) != ATA_ID_GCAP_ATA ||
                (buf[ATA_ID_CAP] & (ATA_ID_CAP_LBA | ATA_ID_CAP_DMA)) !=
                (ATA_ID_CAP_LBA | ATA_ID_CAP_DMA) ||
                (buf[ATA_ID_SUP1] & (ATA_ID_SUP1_VALID_MASK |
                ATA_ID_SUP1_FLUSH | ATA_ID_SUP1_LBA48)) !=
                (ATA_ID_SUP1_VALID | ATA_ID_SUP1_FLUSH | ATA_ID_SUP1_LBA48)) {

                dprintf(V_ERR, ("%s: unsupported ATA device\n",
                        ahci_portname(ps)));

                dprintf(V_DEV, ("%s: GCAP %04x CAP %04x SUP1 %04x\n",
                        ahci_portname(ps), buf[ATA_ID_GCAP], buf[ATA_ID_CAP],
                        buf[ATA_ID_SUP1]));

                return FALSE;
        }

        /* Get number of LBA blocks, and sector size. */
        ps->lba_count = make64((buf[ATA_ID_LBA1] << 16) | buf[ATA_ID_LBA0],
                        (buf[ATA_ID_LBA3] << 16) | buf[ATA_ID_LBA2]);

        /* Determine the queue depth of the device. */
        if (hba_state.has_ncq &&
                        (buf[ATA_ID_SATA_CAP] & ATA_ID_SATA_CAP_NCQ)) {
                ps->flags |= FLAG_HAS_NCQ;
                ps->queue_depth =
                        (buf[ATA_ID_QDEPTH] & ATA_ID_QDEPTH_MASK) + 1;
                if (ps->queue_depth > hba_state.nr_cmds)
                        ps->queue_depth = hba_state.nr_cmds;
        }

        /* For now, we only support long logical sectors. Long physical sector
         * support may be added later. Note that the given value is in words.
         */
        if ((buf[ATA_ID_PLSS] & (ATA_ID_PLSS_VALID_MASK | ATA_ID_PLSS_LLS)) ==
                (ATA_ID_PLSS_VALID | ATA_ID_PLSS_LLS))
                ps->sector_size =
                        ((buf[ATA_ID_LSS1] << 16) | buf[ATA_ID_LSS0]) << 1;
        else
                ps->sector_size = ATA_SECTOR_SIZE;

        if (ps->sector_size < ATA_SECTOR_SIZE) {
                dprintf(V_ERR, ("%s: invalid sector size %u\n",
                        ahci_portname(ps), ps->sector_size));

                return FALSE;
        }

        ps->flags |= FLAG_HAS_MEDIUM | FLAG_HAS_FLUSH;

        /* FLUSH CACHE is mandatory for ATA devices; write caches are not. */
        if (buf[ATA_ID_SUP0] & ATA_ID_SUP0_WCACHE)
                ps->flags |= FLAG_HAS_WCACHE;

        /* Check Force Unit Access capability of the device. */
        if ((buf[ATA_ID_ENA2] & (ATA_ID_ENA2_VALID_MASK | ATA_ID_ENA2_FUA)) ==
                (ATA_ID_ENA2_VALID | ATA_ID_ENA2_FUA))
                ps->flags |= FLAG_HAS_FUA;

        return TRUE;
}

/*===========================================================================*
 *                              ata_transfer                                 *
 *===========================================================================*/
static int ata_transfer(struct port_state *ps, int cmd, u64_t start_lba,
        unsigned int count, int write, int force, prd_t *prdt, int nr_prds)
{
        /* Perform data transfer from or to an ATA device.
         */
        cmd_fis_t fis;

        assert(count <= ATA_MAX_SECTORS);

        /* Special case for sector counts: 65536 is specified as 0. */
        if (count == ATA_MAX_SECTORS)
                count = 0;

        memset(&fis, 0, sizeof(fis));
        fis.cf_dev = ATA_DEV_LBA;
        if (ps->flags & FLAG_HAS_NCQ) {
                if (write) {
                        if (force && (ps->flags & FLAG_HAS_FUA))
                                fis.cf_dev |= ATA_DEV_FUA;

                        fis.cf_cmd = ATA_CMD_WRITE_FPDMA_QUEUED;
                } else {
                        fis.cf_cmd = ATA_CMD_READ_FPDMA_QUEUED;
                }
        }
        else {
                if (write) {
                        if (force && (ps->flags & FLAG_HAS_FUA))
                                fis.cf_cmd = ATA_CMD_WRITE_DMA_FUA_EXT;
                        else
                                fis.cf_cmd = ATA_CMD_WRITE_DMA_EXT;
                }
                else {
                        fis.cf_cmd = ATA_CMD_READ_DMA_EXT;
                }
        }
        fis.cf_lba = ex64lo(start_lba) & 0x00FFFFFFL;
        fis.cf_lba_exp = ex64lo(rshift64(start_lba, 24)) & 0x00FFFFFFL;
        fis.cf_sec = count & 0xFF;
        fis.cf_sec_exp = (count >> 8) & 0xFF;

        /* Start the command, and wait for it to complete or fail. */
        port_set_cmd(ps, cmd, &fis, NULL /*packet*/, prdt, nr_prds, write);

        return port_exec(ps, cmd, ahci_transfer_timeout);
}

/*===========================================================================*
 *                              gen_identify                                 *
 *===========================================================================*/
static int gen_identify(struct port_state *ps, int blocking)
{
        /* Identify an ATA or ATAPI device. If the blocking flag is set, block
         * until the command has completed; otherwise return immediately.
         */
        cmd_fis_t fis;
        prd_t prd;

        /* Set up a command, and a single PRD for the result. */
        memset(&fis, 0, sizeof(fis));

        if (ps->flags & FLAG_ATAPI)
                fis.cf_cmd = ATA_CMD_IDENTIFY_PACKET;
        else
                fis.cf_cmd = ATA_CMD_IDENTIFY;

        prd.vp_addr = ps->tmp_phys;
        prd.vp_size = ATA_ID_SIZE;

        /* Start the command, and possibly wait for the result. */
        port_set_cmd(ps, 0, &fis, NULL /*packet*/, &prd, 1, FALSE /*write*/);

        if (blocking)
                return port_exec(ps, 0, ahci_command_timeout);

        port_issue(ps, 0, ahci_command_timeout);

        return OK;
}

/*===========================================================================*
 *                              gen_flush_wcache                             *
 *===========================================================================*/
static int gen_flush_wcache(struct port_state *ps)
{
        /* Flush the device's write cache.
         */
        cmd_fis_t fis;

        /* The FLUSH CACHE command may not be supported by all (writable ATAPI)
         * devices.
         */
        if (!(ps->flags & FLAG_HAS_FLUSH))
                return EINVAL;

        /* Use the FLUSH CACHE command for both ATA and ATAPI. We are not
         * interested in the disk location of a failure, so there is no reason
         * to use the ATA-only FLUSH CACHE EXT command. Either way, the command
         * may indeed fail due to a disk error, in which case it should be
         * repeated. For now, we shift this responsibility onto the caller.
         */
        memset(&fis, 0, sizeof(fis));
        fis.cf_cmd = ATA_CMD_FLUSH_CACHE;

        /* Start the command, and wait for it to complete or fail.
         * The flush command may take longer than regular I/O commands.
         */
        port_set_cmd(ps, 0, &fis, NULL /*packet*/, NULL /*prdt*/, 0,
                FALSE /*write*/);

        return port_exec(ps, 0, ahci_flush_timeout);
}

/*===========================================================================*
 *                              gen_get_wcache                               *
 *===========================================================================*/
static int gen_get_wcache(struct port_state *ps, int *val)
{
        /* Retrieve the status of the device's write cache.
         */
        int r;

        /* Write caches are not mandatory. */
        if (!(ps->flags & FLAG_HAS_WCACHE))
                return EINVAL;

        /* Retrieve information about the device. */
        if ((r = gen_identify(ps, TRUE /*blocking*/)) != OK)
                return r;

        /* Return the current setting. */
        *val = !!(((u16_t *) ps->tmp_base)[ATA_ID_ENA0] & ATA_ID_ENA0_WCACHE);

        return OK;
}

/*===========================================================================*
 *                              gen_set_wcache                               *
 *===========================================================================*/
static int gen_set_wcache(struct port_state *ps, int enable)
{
        /* Enable or disable the device's write cache.
         */
        cmd_fis_t fis;
        clock_t timeout;

        /* Write caches are not mandatory. */
        if (!(ps->flags & FLAG_HAS_WCACHE))
                return EINVAL;

        /* Disabling the write cache causes a (blocking) cache flush. Cache
         * flushes may take much longer than regular commands.
         */
        timeout = enable ? ahci_command_timeout : ahci_flush_timeout;

        /* Set up a command. */
        memset(&fis, 0, sizeof(fis));
        fis.cf_cmd = ATA_CMD_SET_FEATURES;
        fis.cf_feat = enable ? ATA_SF_EN_WCACHE : ATA_SF_DI_WCACHE;

        /* Start the command, and wait for it to complete or fail. */
        port_set_cmd(ps, 0, &fis, NULL /*packet*/, NULL /*prdt*/, 0,
                FALSE /*write*/);

        return port_exec(ps, 0, timeout);
}

/*===========================================================================*
 *                              ct_set_fis                                   *
 *===========================================================================*/
static vir_bytes ct_set_fis(u8_t *ct, cmd_fis_t *fis, unsigned int tag)
{
        /* Fill in the Frame Information Structure part of a command table,
         * and return the resulting FIS size (in bytes). We only support the
         * command Register - Host to Device FIS type.
         */

        memset(ct, 0, ATA_H2D_SIZE);
        ct[ATA_FIS_TYPE] = ATA_FIS_TYPE_H2D;
        ct[ATA_H2D_FLAGS] = ATA_H2D_FLAGS_C;
        ct[ATA_H2D_CMD] = fis->cf_cmd;
        ct[ATA_H2D_LBA_LOW] = fis->cf_lba & 0xFF;
        ct[ATA_H2D_LBA_MID] = (fis->cf_lba >> 8) & 0xFF;
        ct[ATA_H2D_LBA_HIGH] = (fis->cf_lba >> 16) & 0xFF;
        ct[ATA_H2D_DEV] = fis->cf_dev;
        ct[ATA_H2D_LBA_LOW_EXP] = fis->cf_lba_exp & 0xFF;
        ct[ATA_H2D_LBA_MID_EXP] = (fis->cf_lba_exp >> 8) & 0xFF;
        ct[ATA_H2D_LBA_HIGH_EXP] = (fis->cf_lba_exp >> 16) & 0xFF;
        ct[ATA_H2D_CTL] = fis->cf_ctl;

        if (ATA_IS_FPDMA_CMD(fis->cf_cmd)) {
                ct[ATA_H2D_FEAT] = fis->cf_sec;
                ct[ATA_H2D_FEAT_EXP] = fis->cf_sec_exp;
                ct[ATA_H2D_SEC] = tag << ATA_SEC_TAG_SHIFT;
                ct[ATA_H2D_SEC_EXP] = 0;
        } else {
                ct[ATA_H2D_FEAT] = fis->cf_feat;
                ct[ATA_H2D_FEAT_EXP] = fis->cf_feat_exp;
                ct[ATA_H2D_SEC] = fis->cf_sec;
                ct[ATA_H2D_SEC_EXP] = fis->cf_sec_exp;
        }

        return ATA_H2D_SIZE;
}

/*===========================================================================*
 *                              ct_set_packet                                *
 *===========================================================================*/
static void ct_set_packet(u8_t *ct, u8_t packet[ATAPI_PACKET_SIZE])
{
        /* Fill in the packet part of a command table.
         */

        memcpy(&ct[AHCI_CT_PACKET_OFF], packet, ATAPI_PACKET_SIZE);
}

/*===========================================================================*
 *                              ct_set_prdt                                  *
 *===========================================================================*/
static void ct_set_prdt(u8_t *ct, prd_t *prdt, int nr_prds)
{
        /* Fill in the PRDT part of a command table.
         */
        u32_t *p;
        int i;

        p = (u32_t *) &ct[AHCI_CT_PRDT_OFF];

        for (i = 0; i < nr_prds; i++, prdt++) {
                *p++ = prdt->vp_addr;
                *p++ = 0;
                *p++ = 0;
                *p++ = prdt->vp_size - 1;
        }
}

/*===========================================================================*
 *                              port_set_cmd                                 *
 *===========================================================================*/
static void port_set_cmd(struct port_state *ps, int cmd, cmd_fis_t *fis,
        u8_t packet[ATAPI_PACKET_SIZE], prd_t *prdt, int nr_prds, int write)
{
        /* Prepare the given command for execution, by constructing a command
         * table and setting up a command list entry pointing to the table.
         */
        u8_t *ct;
        u32_t *cl;
        vir_bytes size;

        /* Set a port-specific flag that tells us if the command being
         * processed is a NCQ command or not.
         */
        if (ATA_IS_FPDMA_CMD(fis->cf_cmd)) {
                ps->flags |= FLAG_NCQ_MODE;
        } else {
                assert(!ps->pend_mask);
                ps->flags &= ~FLAG_NCQ_MODE;
        }

        /* Construct a command table, consisting of a command FIS, optionally
         * a packet, and optionally a number of PRDs (making up the actual PRD
         * table).
         */
        ct = ps->ct_base[cmd];

        assert(ct != NULL);
        assert(nr_prds <= NR_PRDS);

        size = ct_set_fis(ct, fis, cmd);

        if (packet != NULL)
                ct_set_packet(ct, packet);

        ct_set_prdt(ct, prdt, nr_prds);

        /* Construct a command list entry, pointing to the command's table.
         * Current assumptions: callers always provide a Register - Host to
         * Device type FIS, and all non-NCQ commands are prefetchable.
         */
        cl = &ps->cl_base[cmd * AHCI_CL_ENTRY_DWORDS];

        memset(cl, 0, AHCI_CL_ENTRY_SIZE);
        cl[0] = (nr_prds << AHCI_CL_PRDTL_SHIFT) |
                ((!ATA_IS_FPDMA_CMD(fis->cf_cmd) &&
                (nr_prds > 0 || packet != NULL)) ? AHCI_CL_PREFETCHABLE : 0) |
                (write ? AHCI_CL_WRITE : 0) |
                ((packet != NULL) ? AHCI_CL_ATAPI : 0) |
                ((size / sizeof(u32_t)) << AHCI_CL_CFL_SHIFT);
        cl[2] = ps->ct_phys[cmd];
}

/*===========================================================================*
 *                              port_finish_cmd                              *
 *===========================================================================*/
static void port_finish_cmd(struct port_state *ps, int cmd, int result)
{
        /* Finish a command that has either succeeded or failed.
         */

        assert(cmd < ps->queue_depth);

        dprintf(V_REQ, ("%s: command %d %s\n", ahci_portname(ps),
                cmd, (result == RESULT_SUCCESS) ? "succeeded" : "failed"));

        /* Update the command result, and clear it from the pending list. */
        ps->cmd_info[cmd].result = result;

        assert(ps->pend_mask & (1 << cmd));
        ps->pend_mask &= ~(1 << cmd);

        /* Wake up the thread, unless it is the main thread. This can happen
         * during initialization, as the gen_identify function is called by the
         * main thread itself.
         */
        if (ps->state != STATE_WAIT_ID)
                blockdriver_mt_wakeup(ps->cmd_info[cmd].tid);
}

/*===========================================================================*
 *                              port_fail_cmds                               *
 *===========================================================================*/
static void port_fail_cmds(struct port_state *ps)
{
        /* Fail all ongoing commands for a device.
         */
        int i;

        for (i = 0; ps->pend_mask != 0 && i < ps->queue_depth; i++)
                if (ps->pend_mask & (1 << i))
                        port_finish_cmd(ps, i, RESULT_FAILURE);
}

/*===========================================================================*
 *                              port_check_cmds                              *
 *===========================================================================*/
static void port_check_cmds(struct port_state *ps)
{
        /* Check what commands have completed, and finish them.
         */
        u32_t mask, done;
        int i;

        /* See which commands have completed. */
        if (ps->flags & FLAG_NCQ_MODE)
                mask = ps->reg[AHCI_PORT_SACT];
        else
                mask = ps->reg[AHCI_PORT_CI];

        /* Wake up threads corresponding to completed commands. */
        done = ps->pend_mask & ~mask;

        for (i = 0; i < ps->queue_depth; i++)
                if (done & (1 << i))
                        port_finish_cmd(ps, i, RESULT_SUCCESS);
}

/*===========================================================================*
 *                              port_find_cmd                                *
 *===========================================================================*/
static int port_find_cmd(struct port_state *ps)
{
        /* Find a free command tag to queue the current request.
         */
        int i;

        for (i = 0; i < ps->queue_depth; i++)
                if (!(ps->pend_mask & (1 << i)))
                        break;

        /* We should always be able to find a free slot, since a thread runs
         * only when it is free, and thus, only because a slot is available.
         */
        assert(i < ps->queue_depth);

        return i;
}

/*===========================================================================*
 *                              port_get_padbuf                              *
 *===========================================================================*/
static int port_get_padbuf(struct port_state *ps, size_t size)
{
        /* Make available a temporary buffer for use by this port. Enlarge the
         * previous buffer if applicable and necessary, potentially changing
         * its physical address.
         */

        if (ps->pad_base != NULL && ps->pad_size >= size)
                return OK;

        if (ps->pad_base != NULL)
                free_contig(ps->pad_base, ps->pad_size);

        ps->pad_size = size;
        ps->pad_base = alloc_contig(ps->pad_size, 0, &ps->pad_phys);

        if (ps->pad_base == NULL) {
                dprintf(V_ERR, ("%s: unable to allocate a padding buffer of "
                        "size %lu\n", ahci_portname(ps),
                        (unsigned long) size));

                return ENOMEM;
        }

        dprintf(V_INFO, ("%s: allocated padding buffer of size %lu\n",
                ahci_portname(ps), (unsigned long) size));

        return OK;
}

/*===========================================================================*
 *                              sum_iovec                                    *
 *===========================================================================*/
static int sum_iovec(struct port_state *ps, endpoint_t endpt,
        iovec_s_t *iovec, int nr_req, vir_bytes *total)
{
        /* Retrieve the total size of the given I/O vector. Check for alignment
         * requirements along the way. Return OK (and the total request size)
         * or an error.
         */
        vir_bytes size, bytes;
        int i;

        bytes = 0;

        for (i = 0; i < nr_req; i++) {
                size = iovec[i].iov_size;

                if (size == 0 || (size & 1) || size > LONG_MAX) {
                        dprintf(V_ERR, ("%s: bad size %lu in iovec from %d\n",
                                ahci_portname(ps), size, endpt));
                        return EINVAL;
                }

                bytes += size;

                if (bytes > LONG_MAX) {
                        dprintf(V_ERR, ("%s: iovec size overflow from %d\n",
                                ahci_portname(ps), endpt));
                        return EINVAL;
                }
        }

        *total = bytes;
        return OK;
}

/*===========================================================================*
 *                              setup_prdt                                   *
 *===========================================================================*/
static int setup_prdt(struct port_state *ps, endpoint_t endpt,
        iovec_s_t *iovec, int nr_req, vir_bytes size, vir_bytes lead,
        int write, prd_t *prdt)
{
        /* Convert (the first part of) an I/O vector to a Physical Region
         * Descriptor Table describing array that can later be used to set the
         * command's real PRDT. The resulting table as a whole should be
         * sector-aligned; leading and trailing local buffers may have to be
         * used for padding as appropriate. Return the number of PRD entries,
         * or a negative error code.
         */
        struct vumap_vir vvec[NR_PRDS];
        size_t bytes, trail;
        int i, r, pcount, nr_prds = 0;

        if (lead > 0) {
                /* Allocate a buffer for the data we don't want. */
                if ((r = port_get_padbuf(ps, ps->sector_size)) != OK)
                        return r;

                prdt[nr_prds].vp_addr = ps->pad_phys;
                prdt[nr_prds].vp_size = lead;
                nr_prds++;
        }

        /* The sum of lead, size, trail has to be sector-aligned. */
        trail = (ps->sector_size - (lead + size)) % ps->sector_size;

        /* Get the physical addresses of the given buffers. */
        for (i = 0; i < nr_req && size > 0; i++) {
                bytes = MIN(iovec[i].iov_size, size);

                if (endpt == SELF)
                        vvec[i].vv_addr = (vir_bytes) iovec[i].iov_grant;
                else
                        vvec[i].vv_grant = iovec[i].iov_grant;

                vvec[i].vv_size = bytes;

                size -= bytes;
        }

        pcount = i;

        if ((r = sys_vumap(endpt, vvec, i, 0, write ? VUA_READ : VUA_WRITE,
                        &prdt[nr_prds], &pcount)) != OK) {
                dprintf(V_ERR, ("%s: unable to map memory from %d (%d)\n",
                        ahci_portname(ps), endpt, r));
                return r;
        }

        assert(pcount > 0 && pcount <= i);

        /* Make sure all buffers are physically contiguous and word-aligned. */
        for (i = 0; i < pcount; i++) {
                if (vvec[i].vv_size != prdt[nr_prds].vp_size) {
                        dprintf(V_ERR, ("%s: non-contiguous memory from %d\n",
                                ahci_portname(ps), endpt));
                        return EINVAL;
                }

                if (prdt[nr_prds].vp_addr & 1) {
                        dprintf(V_ERR, ("%s: bad physical address from %d\n",
                                ahci_portname(ps), endpt));
                        return EINVAL;
                }

                nr_prds++;
        }

        if (trail > 0) {
                assert(nr_prds < NR_PRDS);
                prdt[nr_prds].vp_addr = ps->pad_phys + lead;
                prdt[nr_prds].vp_size = trail;
                nr_prds++;
        }

        return nr_prds;
}

/*===========================================================================*
 *                              port_transfer                                *
 *===========================================================================*/
static ssize_t port_transfer(struct port_state *ps, u64_t pos, u64_t eof,
        endpoint_t endpt, iovec_s_t *iovec, int nr_req, int write, int flags)
{
        /* Perform an I/O transfer on a port.
         */
        prd_t prdt[NR_PRDS];
        vir_bytes size, lead;
        unsigned int count, nr_prds;
        u64_t start_lba;
        int r, cmd;

        /* Get the total request size from the I/O vector. */
        if ((r = sum_iovec(ps, endpt, iovec, nr_req, &size)) != OK)
                return r;

        dprintf(V_REQ, ("%s: %s for %lu bytes at pos %08lx%08lx\n",
                ahci_portname(ps), write ? "write" : "read", size,
                ex64hi(pos), ex64lo(pos)));

        assert(ps->state == STATE_GOOD_DEV);
        assert(ps->flags & FLAG_HAS_MEDIUM);
        assert(ps->sector_size > 0);

        /* Limit the maximum size of a single transfer.
         * See the comments at the top of this file for details.
         */
        if (size > MAX_TRANSFER)
                size = MAX_TRANSFER;

        /* If necessary, reduce the request size so that the request does not
         * extend beyond the end of the partition. The caller already
         * guarantees that the starting position lies within the partition.
         */
        if (cmp64(add64ul(pos, size), eof) >= 0)
                size = (vir_bytes) diff64(eof, pos);

        start_lba = div64(pos, cvu64(ps->sector_size));
        lead = rem64u(pos, ps->sector_size);
        count = (lead + size + ps->sector_size - 1) / ps->sector_size;

        /* Position must be word-aligned for read requests, and sector-aligned
         * for write requests. We do not support read-modify-write for writes.
         */
        if ((lead & 1) || (write && lead != 0)) {
                dprintf(V_ERR, ("%s: unaligned position from %d\n",
                        ahci_portname(ps), endpt));
                return EINVAL;
        }

        /* Write requests must be sector-aligned. Word alignment of the size is
         * already guaranteed by sum_iovec().
         */
        if (write && (size % ps->sector_size) != 0) {
                dprintf(V_ERR, ("%s: unaligned size %lu from %d\n",
                        ahci_portname(ps), size, endpt));
                return EINVAL;
        }

        /* Create a vector of physical addresses and sizes for the transfer. */
        nr_prds = r = setup_prdt(ps, endpt, iovec, nr_req, size, lead, write,
                prdt);

        if (r < 0) return r;

        /* Perform the actual transfer. */
        cmd = port_find_cmd(ps);

        if (ps->flags & FLAG_ATAPI)
                r = atapi_transfer(ps, cmd, start_lba, count, write, prdt,
                        nr_prds);
        else
                r = ata_transfer(ps, cmd, start_lba, count, write,
                        !!(flags & BDEV_FORCEWRITE), prdt, nr_prds);

        if (r != OK) return r;

        return size;
}

/*===========================================================================*
 *                              port_start                                   *
 *===========================================================================*/
static void port_start(struct port_state *ps)
{
        /* Start the given port, allowing for the execution of commands and the
         * transfer of data on that port.
         */
        u32_t cmd;

        /* Enable FIS receive. */
        cmd = ps->reg[AHCI_PORT_CMD];
        ps->reg[AHCI_PORT_CMD] = cmd | AHCI_PORT_CMD_FRE;

        /* Reset status registers. */
        ps->reg[AHCI_PORT_SERR] = ~0;
        ps->reg[AHCI_PORT_IS] = ~0;

        /* Start the port. */
        cmd = ps->reg[AHCI_PORT_CMD];
        ps->reg[AHCI_PORT_CMD] = cmd | AHCI_PORT_CMD_ST;

        dprintf(V_INFO, ("%s: started\n", ahci_portname(ps)));
}

/*===========================================================================*
 *                              port_restart                                 *
 *===========================================================================*/
static void port_restart(struct port_state *ps)
{
        /* Restart a port after a fatal error has occurred.
         */
        u32_t cmd;

        /* Fail all outstanding commands. */
        port_fail_cmds(ps);

        /* Stop the port. */
        cmd = ps->reg[AHCI_PORT_CMD];
        ps->reg[AHCI_PORT_CMD] = cmd & ~AHCI_PORT_CMD_ST;

        SPIN_UNTIL(!(ps->reg[AHCI_PORT_CMD] & AHCI_PORT_CMD_CR),
                PORTREG_DELAY);

        /* Reset status registers. */
        ps->reg[AHCI_PORT_SERR] = ~0;
        ps->reg[AHCI_PORT_IS] = ~0;

        /* If the BSY and/or DRQ flags are set, reset the port. */
        if (ps->reg[AHCI_PORT_TFD] &
                (AHCI_PORT_TFD_STS_BSY | AHCI_PORT_TFD_STS_DRQ)) {

                dprintf(V_ERR, ("%s: port reset\n", ahci_portname(ps)));

                /* Trigger a port reset. */
                ps->reg[AHCI_PORT_SCTL] = AHCI_PORT_SCTL_DET_INIT;
                micro_delay(SPINUP_DELAY * 1000);
                ps->reg[AHCI_PORT_SCTL] = AHCI_PORT_SCTL_DET_NONE;

                /* To keep this driver simple, we do not transparently recover
                 * ongoing requests. Instead, we mark the failing device as
                 * disconnected, and assume that if the reset succeeds, the
                 * device (or, perhaps, eventually, another device) will come
                 * back up. Any current and future requests to this port will
                 * be failed until the port is fully closed and reopened.
                 */
                port_disconnect(ps);

                return;
        }

        /* Start the port. */
        cmd = ps->reg[AHCI_PORT_CMD];
        ps->reg[AHCI_PORT_CMD] = cmd | AHCI_PORT_CMD_ST;

        dprintf(V_INFO, ("%s: restarted\n", ahci_portname(ps)));
}

/*===========================================================================*
 *                              port_stop                                    *
 *===========================================================================*/
static void port_stop(struct port_state *ps)
{
        /* Stop the given port, if not already stopped.
         */
        u32_t cmd;

        /* Disable interrupts. */
        ps->reg[AHCI_PORT_IE] = AHCI_PORT_IE_NONE;

        /* Stop the port. */
        cmd = ps->reg[AHCI_PORT_CMD];

        if (cmd & (AHCI_PORT_CMD_CR | AHCI_PORT_CMD_ST)) {
                cmd &= ~(AHCI_PORT_CMD_CR | AHCI_PORT_CMD_ST);

                ps->reg[AHCI_PORT_CMD] = cmd;

                SPIN_UNTIL(!(ps->reg[AHCI_PORT_CMD] & AHCI_PORT_CMD_CR),
                        PORTREG_DELAY);

                dprintf(V_INFO, ("%s: stopped\n", ahci_portname(ps)));

                cmd = ps->reg[AHCI_PORT_CMD];
        }

        if (cmd & (AHCI_PORT_CMD_FR | AHCI_PORT_CMD_FRE)) {
                cmd &= ~(AHCI_PORT_CMD_FR | AHCI_PORT_CMD_FRE);

                ps->reg[AHCI_PORT_CMD] = cmd;

                SPIN_UNTIL(!(ps->reg[AHCI_PORT_CMD] & AHCI_PORT_CMD_FR),
                        PORTREG_DELAY);
        }

        /* Reset status registers. */
        ps->reg[AHCI_PORT_SERR] = ~0;
        ps->reg[AHCI_PORT_IS] = ~0;
}

/*===========================================================================*
 *                              port_sig_check                               *
 *===========================================================================*/
static void port_sig_check(struct port_state *ps)
{
        /* Check whether the device's signature has become available yet, and
         * if so, start identifying the device.
         */
        u32_t tfd, sig;

        tfd = ps->reg[AHCI_PORT_TFD];

        /* Wait for the BSY flag to be (set and then) cleared first. Note that
         * clearing it only happens when PxCMD.FRE is set, which is why we
         * start the port before starting the signature wait cycle.
         */
        if ((tfd & AHCI_PORT_TFD_STS_BSY) || tfd == AHCI_PORT_TFD_STS_INIT) {
                /* Try for a while before giving up. It may take seconds. */
                if (ps->left > 0) {
                        ps->left--;
                        set_timer(&ps->cmd_info[0].timer, ahci_sig_timeout,
                                port_timeout, BUILD_ARG(ps - port_state, 0));
                        return;
                }

                /* If no device is actually attached, disable the port. This
                 * value is also the initial value of the register, before the
                 * BSY flag gets set, so only check this condition on timeout.
                 */
                if (tfd == AHCI_PORT_TFD_STS_INIT) {
                        dprintf(V_DEV, ("%s: no device at this port\n",
                                ahci_portname(ps)));

                        port_stop(ps);

                        ps->state = STATE_BAD_DEV;
                        ps->flags &= ~FLAG_BUSY;

                        return;
                }

                port_restart(ps);

                dprintf(V_ERR, ("%s: timeout waiting for signature\n",
                        ahci_portname(ps)));
        }

        /* Check the port's signature. We only support the normal ATA and ATAPI
         * signatures. We ignore devices reporting anything else.
         */
        sig = ps->reg[AHCI_PORT_SIG];

        if (sig != ATA_SIG_ATA && sig != ATA_SIG_ATAPI) {
                dprintf(V_ERR, ("%s: unsupported signature (%08x)\n",
                        ahci_portname(ps), sig));

                port_stop(ps);

                ps->state = STATE_BAD_DEV;
                ps->flags &= ~FLAG_BUSY;

                return;
        }

        /* Clear all state flags except the busy flag, which may be relevant if
         * a BDEV_OPEN call is waiting for the device to become ready; the
         * barrier flag, which prevents access to the device until it is
         * completely closed and (re)opened; and, the thread suspension flag.
         */
        ps->flags &= (FLAG_BUSY | FLAG_BARRIER | FLAG_SUSPENDED);

        if (sig == ATA_SIG_ATAPI)
                ps->flags |= FLAG_ATAPI;

        /* Attempt to identify the device. Do this using continuation, because
         * we may already be called from port_wait() here, and could end up
         * confusing the timer expiration procedure.
         */
        ps->state = STATE_WAIT_ID;
        ps->reg[AHCI_PORT_IE] = AHCI_PORT_IE_MASK;

        (void) gen_identify(ps, FALSE /*blocking*/);
}

/*===========================================================================*
 *                              print_string                                 *
 *===========================================================================*/
static void print_string(u16_t *buf, int start, int end)
{
        /* Print a string that is stored as little-endian words and padded with
         * trailing spaces.
         */
        int i, last = 0;

        while (end >= start && buf[end] == 0x2020) end--;

        if (end >= start && (buf[end] & 0xFF) == 0x20) end--, last++;

        for (i = start; i <= end; i++)
                printf("%c%c", buf[i] >> 8, buf[i] & 0xFF);

        if (last)
                printf("%c", buf[i] >> 8);
}

/*===========================================================================*
 *                              port_id_check                                *
 *===========================================================================*/
static void port_id_check(struct port_state *ps, int success)
{
        /* The device identification command has either completed or timed out.
         * Decide whether this device is usable or not, and store some of its
         * properties.
         */
        u16_t *buf;

        assert(ps->state == STATE_WAIT_ID);
        assert(!(ps->flags & FLAG_BUSY));       /* unset by callers */

        cancel_timer(&ps->cmd_info[0].timer);

        if (!success)
                dprintf(V_ERR,
                        ("%s: unable to identify\n", ahci_portname(ps)));

        /* If the identify command itself succeeded, check the results and
         * store some properties.
         */
        if (success) {
                buf = (u16_t *) ps->tmp_base;

                if (ps->flags & FLAG_ATAPI)
                        success = atapi_id_check(ps, buf);
                else
                        success = ata_id_check(ps, buf);
        }

        /* If the device has not been identified successfully, mark it as an
         * unusable device.
         */
        if (!success) {
                port_stop(ps);

                ps->state = STATE_BAD_DEV;
                ps->reg[AHCI_PORT_IE] = AHCI_PORT_IE_PRCE;

                return;
        }

        /* The device has been identified successfully, and hence usable. */
        ps->state = STATE_GOOD_DEV;

        /* Print some information about the device. */
        if (ahci_verbose >= V_INFO) {
                printf("%s: ATA%s, ", ahci_portname(ps),
                        (ps->flags & FLAG_ATAPI) ? "PI" : "");
                print_string(buf, 27, 46);
                if (ahci_verbose >= V_DEV) {
                        printf(" (");
                        print_string(buf, 10, 19);
                        printf(", ");
                        print_string(buf, 23, 26);
                        printf(")");
                }

                if (ps->flags & FLAG_HAS_MEDIUM)
                        printf(", %u byte sectors, %lu MB size",
                                ps->sector_size, div64u(mul64(ps->lba_count,
                                cvu64(ps->sector_size)), 1024*1024));

                printf("\n");
        }
}

/*===========================================================================*
 *                              port_connect                                 *
 *===========================================================================*/
static void port_connect(struct port_state *ps)
{
        /* A device has been found to be attached to this port. Start the port,
         * and do timed polling for its signature to become available.
         */

        dprintf(V_INFO, ("%s: device connected\n", ahci_portname(ps)));

        if (ps->state == STATE_SPIN_UP)
                cancel_timer(&ps->cmd_info[0].timer);

        port_start(ps);

        ps->state = STATE_WAIT_SIG;
        ps->left = ahci_sig_checks;

        ps->reg[AHCI_PORT_IE] = AHCI_PORT_IE_PRCE;

        /* Do the first check immediately; who knows, we may get lucky. */
        port_sig_check(ps);
}

/*===========================================================================*
 *                              port_disconnect                              *
 *===========================================================================*/
static void port_disconnect(struct port_state *ps)
{
        /* The device has detached from this port. Stop the port if necessary.
         */

        dprintf(V_INFO, ("%s: device disconnected\n", ahci_portname(ps)));

        if (ps->state != STATE_BAD_DEV)
                port_stop(ps);

        ps->state = STATE_NO_DEV;
        ps->reg[AHCI_PORT_IE] = AHCI_PORT_IE_PRCE;
        ps->flags &= ~FLAG_BUSY;

        /* Fail any ongoing request. The caller may already have done this. */
        port_fail_cmds(ps);

        /* Block any further access until the device is completely closed and
         * reopened. This prevents arbitrary I/O to a newly plugged-in device
         * without upper layers noticing.
         */
        ps->flags |= FLAG_BARRIER;

        /* Inform the blockdriver library to reduce the number of threads. */
        blockdriver_mt_set_workers(ps->device, 1);
}

/*===========================================================================*
 *                              port_intr                                    *
 *===========================================================================*/
static void port_intr(struct port_state *ps)
{
        /* Process an interrupt on this port.
         */
        u32_t smask, emask;
        int connected;

        if (ps->state == STATE_NO_PORT) {
                dprintf(V_ERR, ("%s: interrupt for invalid port!\n",
                        ahci_portname(ps)));

                return;
        }

        smask = ps->reg[AHCI_PORT_IS];
        emask = smask & ps->reg[AHCI_PORT_IE];

        /* Clear the interrupt flags that we saw were set. */
        ps->reg[AHCI_PORT_IS] = smask;

        dprintf(V_REQ, ("%s: interrupt (%08x)\n", ahci_portname(ps), smask));

        /* Check if any commands have completed. */
        port_check_cmds(ps);

        if (emask & AHCI_PORT_IS_PRCS) {
                /* Clear the N diagnostics bit to clear this interrupt. */
                ps->reg[AHCI_PORT_SERR] = AHCI_PORT_SERR_DIAG_N;

                connected =
                        (ps->reg[AHCI_PORT_SSTS] & AHCI_PORT_SSTS_DET_MASK) ==
                        AHCI_PORT_SSTS_DET_PHY;

                switch (ps->state) {
                case STATE_BAD_DEV:
                case STATE_GOOD_DEV:
                case STATE_WAIT_SIG:
                case STATE_WAIT_ID:
                        port_disconnect(ps);

                        /* fall-through */
                default:
                        if (!connected)
                                break;

                        port_connect(ps);
                }
        } else if (smask & AHCI_PORT_IS_MASK) {
                /* We assume that any other interrupt indicates command
                 * completion or (command or device) failure. Unfortunately, if
                 * an NCQ command failed, we cannot easily determine which one
                 * it was. For that reason, after completing all successfully
                 * finished commands (above), we fail all other outstanding
                 * commands and restart the port. This can possibly be improved
                 * later by obtaining per-command status results from the HBA.
                 */

                /* If we were waiting for ID verification, check now. */
                if (ps->state == STATE_WAIT_ID) {
                        ps->flags &= ~FLAG_BUSY;
                        port_id_check(ps, !(ps->reg[AHCI_PORT_TFD] &
                                (AHCI_PORT_TFD_STS_ERR |
                                AHCI_PORT_TFD_STS_DF)));
                }

                /* Check now for failure. There are fatal failures, and there
                 * are failures that set the TFD.STS.ERR field using a D2H
                 * FIS. In both cases, we just restart the port, failing all
                 * commands in the process.
                 */
                if ((ps->reg[AHCI_PORT_TFD] &
                        (AHCI_PORT_TFD_STS_ERR | AHCI_PORT_TFD_STS_DF)) ||
                        (smask & AHCI_PORT_IS_RESTART)) {
                                port_restart(ps);
                }
        }
}

/*===========================================================================*
 *                              port_timeout                                 *
 *===========================================================================*/
static void port_timeout(struct timer *tp)
{
        /* A timeout has occurred on this port. Figure out what the timeout is
         * for, and take appropriate action.
         */
        struct port_state *ps;
        int port, cmd;

        port = GET_PORT(tmr_arg(tp)->ta_int);
        cmd = GET_TAG(tmr_arg(tp)->ta_int);

        assert(port >= 0 && port < hba_state.nr_ports);

        ps = &port_state[port];

        /* Regardless of the outcome of this timeout, wake up the thread if it
         * is suspended. This applies only during the initialization.
         */
        if (ps->flags & FLAG_SUSPENDED) {
                assert(cmd == 0);
                blockdriver_mt_wakeup(ps->cmd_info[0].tid);
        }

        /* If detection of a device after startup timed out, give up on initial
         * detection and only look for hot plug events from now on.
         */
        if (ps->state == STATE_SPIN_UP) {
                /* There is one exception: for braindead controllers that don't
                 * generate the right interrupts (cough, VirtualBox), we do an
                 * explicit check to see if a device is connected after all.
                 * Later hot-(un)plug events will not be detected in this case.
                 */
                if ((ps->reg[AHCI_PORT_SSTS] & AHCI_PORT_SSTS_DET_MASK) ==
                                                AHCI_PORT_SSTS_DET_PHY) {
                        dprintf(V_INFO, ("%s: no device connection event\n",
                                ahci_portname(ps)));

                        port_connect(ps);
                }
                else {
                        dprintf(V_INFO, ("%s: spin-up timeout\n",
                                ahci_portname(ps)));

                        /* If the busy flag is set, a BDEV_OPEN request is
                         * waiting for the detection to finish; clear the busy
                         * flag to return an error to the caller.
                         */
                        ps->state = STATE_NO_DEV;
                        ps->flags &= ~FLAG_BUSY;
                }

                return;
        }

        /* If a device has been connected and we are waiting for its signature
         * to become available, check now.
         */
        if (ps->state == STATE_WAIT_SIG) {
                port_sig_check(ps);

                return;
        }

        /* The only case where the busy flag will be set after this is for a
         * failed identify operation. During this operation, the port will be
         * in the WAIT_ID state. In that case, we clear the BUSY flag, fail the
         * command by setting its state, restart port and finish identify op.
         */
        if (ps->flags & FLAG_BUSY) {
                assert(ps->state == STATE_WAIT_ID);
                ps->flags &= ~FLAG_BUSY;
        }

        dprintf(V_ERR, ("%s: timeout\n", ahci_portname(ps)));

        /* Restart the port, failing all current commands. */
        port_restart(ps);

        /* Finish up the identify operation. */
        if (ps->state == STATE_WAIT_ID)
                port_id_check(ps, FALSE);
}

/*===========================================================================*
 *                              port_wait                                    *
 *===========================================================================*/
static void port_wait(struct port_state *ps)
{
        /* Suspend the current thread until the given port is no longer busy,
         * due to either command completion or timeout.
         */

        ps->flags |= FLAG_SUSPENDED;

        while (ps->flags & FLAG_BUSY)
                blockdriver_mt_sleep();

        ps->flags &= ~FLAG_SUSPENDED;
}

/*===========================================================================*
 *                              port_issue                                   *
 *===========================================================================*/
static void port_issue(struct port_state *ps, int cmd, clock_t timeout)
{
        /* Issue a command to the port, and set a timer to trigger a timeout
         * if the command takes too long to complete.
         */

        /* Set the corresponding NCQ command bit, if applicable. */
        if (ps->flags & FLAG_HAS_NCQ)
                ps->reg[AHCI_PORT_SACT] = (1 << cmd);

        /* Make sure that the compiler does not delay any previous write
         * operations until after the write to the command issue register.
         */
        __insn_barrier();

        /* Tell the controller that a new command is ready. */
        ps->reg[AHCI_PORT_CI] = (1 << cmd);

        /* Update pending commands. */
        ps->pend_mask |= 1 << cmd;

        /* Set a timer in case the command does not complete at all. */
        set_timer(&ps->cmd_info[cmd].timer, timeout, port_timeout,
                BUILD_ARG(ps - port_state, cmd));
}

/*===========================================================================*
 *                              port_exec                                    *
 *===========================================================================*/
static int port_exec(struct port_state *ps, int cmd, clock_t timeout)
{
        /* Execute a command on a port, wait for the command to complete or for
         * a timeout, and return whether the command succeeded or not.
         */

        port_issue(ps, cmd, timeout);

        /* Put the thread to sleep until a timeout or a command completion
         * happens. Earlier, we used to call port_wait which set the suspended
         * flag. We now abandon it since the flag has to work on a per-thread,
         * and hence per-tag basis and not on a per-port basis. Instead, we
         * retain that call only to defer open calls during device/driver
         * initialization. Instead, we call sleep here directly. Before
         * sleeping, we register the thread.
         */
        ps->cmd_info[cmd].tid = blockdriver_mt_get_tid();

        blockdriver_mt_sleep();

        /* Cancelling a timer that just triggered, does no harm. */
        cancel_timer(&ps->cmd_info[cmd].timer);

        assert(!(ps->flags & FLAG_BUSY));

        dprintf(V_REQ, ("%s: end of command -- %s\n", ahci_portname(ps),
                (ps->cmd_info[cmd].result == RESULT_FAILURE) ?
                "failure" : "success"));

        if (ps->cmd_info[cmd].result == RESULT_FAILURE)
                return EIO;

        return OK;
}

/*===========================================================================*
 *                              port_alloc                                   *
 *===========================================================================*/
static void port_alloc(struct port_state *ps)
{
        /* Allocate memory for the given port. We try to cram everything into
         * one 4K-page in order to limit memory usage as much as possible.
         * More memory may be allocated on demand later, but allocation failure
         * should be fatal only here. Note that we do not allocate memory for
         * sector padding here, because we do not know the device's sector size
         * yet.
         */
        size_t fis_off, tmp_off, ct_off; int i;
        size_t ct_offs[NR_CMDS];

        fis_off = AHCI_CL_SIZE + AHCI_FIS_SIZE - 1;
        fis_off -= fis_off % AHCI_FIS_SIZE;

        tmp_off = fis_off + AHCI_FIS_SIZE + AHCI_TMP_ALIGN - 1;
        tmp_off -= tmp_off % AHCI_TMP_ALIGN;

        /* Allocate memory for all the commands. */
        ct_off = tmp_off + AHCI_TMP_SIZE;
        for (i = 0; i < NR_CMDS; i++) {
                ct_off += AHCI_CT_ALIGN - 1;
                ct_off -= ct_off % AHCI_CT_ALIGN;
                ct_offs[i] = ct_off;
                ps->mem_size = ct_off + AHCI_CT_SIZE;
                ct_off = ps->mem_size;
        }

        ps->mem_base = alloc_contig(ps->mem_size, AC_ALIGN4K, &ps->mem_phys);
        if (ps->mem_base == NULL)
                panic("unable to allocate port memory");
        memset(ps->mem_base, 0, ps->mem_size);

        ps->cl_base = (u32_t *) ps->mem_base;
        ps->cl_phys = ps->mem_phys;
        assert(ps->cl_phys % AHCI_CL_SIZE == 0);

        ps->fis_base = (u32_t *) (ps->mem_base + fis_off);
        ps->fis_phys = ps->mem_phys + fis_off;
        assert(ps->fis_phys % AHCI_FIS_SIZE == 0);

        ps->tmp_base = (u8_t *) (ps->mem_base + tmp_off);
        ps->tmp_phys = ps->mem_phys + tmp_off;
        assert(ps->tmp_phys % AHCI_TMP_ALIGN == 0);

        for (i = 0; i < NR_CMDS; i++) {
                ps->ct_base[i] = ps->mem_base + ct_offs[i];
                ps->ct_phys[i] = ps->mem_phys + ct_offs[i];
                assert(ps->ct_phys[i] % AHCI_CT_ALIGN == 0);
        }

        /* Tell the controller about some of the physical addresses. */
        ps->reg[AHCI_PORT_FBU] = 0;
        ps->reg[AHCI_PORT_FB] = ps->fis_phys;

        ps->reg[AHCI_PORT_CLBU] = 0;
        ps->reg[AHCI_PORT_CLB] = ps->cl_phys;

        ps->pad_base = NULL;
        ps->pad_size = 0;
}

/*===========================================================================*
 *                              port_free                                    *
 *===========================================================================*/
static void port_free(struct port_state *ps)
{
        /* Free previously allocated memory for the given port.
         */
        int i;

        if (ps->pad_base != NULL)
                free_contig(ps->pad_base, ps->pad_size);

        /* The first command table is part of the primary memory page. */
        for (i = 1; i < hba_state.nr_cmds; i++)
                if (ps->ct_base[i] != NULL)
                        free_contig(ps->ct_base[i], AHCI_CT_SIZE);

        free_contig(ps->mem_base, ps->mem_size);
}

/*===========================================================================*
 *                              port_init                                    *
 *===========================================================================*/
static void port_init(struct port_state *ps)
{
        /* Initialize the given port.
         */
        u32_t cmd;
        int i;

        /* Initialize the port state structure. */
        ps->queue_depth = 1;
        ps->state = STATE_SPIN_UP;
        ps->flags = FLAG_BUSY;
        ps->sector_size = 0;
        ps->open_count = 0;
        ps->pend_mask = 0;
        for (i = 0; i < NR_CMDS; i++)
                init_timer(&ps->cmd_info[i].timer);

        ps->reg = (u32_t *) ((u8_t *) hba_state.base +
                AHCI_MEM_BASE_SIZE + AHCI_MEM_PORT_SIZE * (ps - port_state));

        /* Make sure the port is in a known state. */
        port_stop(ps);

        /* Allocate memory for the port. */
        port_alloc(ps);

        /* Just listen for device status change events for now. */
        ps->reg[AHCI_PORT_IE] = AHCI_PORT_IE_PRCE;

        /* Perform a reset on the device. */
        cmd = ps->reg[AHCI_PORT_CMD];
        ps->reg[AHCI_PORT_CMD] = cmd | AHCI_PORT_CMD_SUD;

        ps->reg[AHCI_PORT_SCTL] = AHCI_PORT_SCTL_DET_INIT;
        micro_delay(SPINUP_DELAY * 1000);       /* SPINUP_DELAY is in ms */
        ps->reg[AHCI_PORT_SCTL] = AHCI_PORT_SCTL_DET_NONE;

        set_timer(&ps->cmd_info[0].timer, ahci_spinup_timeout,
                port_timeout, BUILD_ARG(ps - port_state, 0));
}

/*===========================================================================*
 *                              ahci_probe                                   *
 *===========================================================================*/
static int ahci_probe(int skip)
{
        /* Find a matching PCI device.
         */
        int r, devind;
        u16_t vid, did;

        pci_init();

        r = pci_first_dev(&devind, &vid, &did);
        if (r <= 0)
                return -1;

        while (skip--) {
                r = pci_next_dev(&devind, &vid, &did);
                if (r <= 0)
                        return -1;
        }

        pci_reserve(devind);

        return devind;
}

/*===========================================================================*
 *                              ahci_reset                                   *
 *===========================================================================*/
static void ahci_reset(void)
{
        /* Reset the HBA. Do not enable AHCI mode afterwards.
         */
        u32_t ghc;

        ghc = hba_state.base[AHCI_HBA_GHC];

        hba_state.base[AHCI_HBA_GHC] = ghc | AHCI_HBA_GHC_AE;

        hba_state.base[AHCI_HBA_GHC] = ghc | AHCI_HBA_GHC_AE | AHCI_HBA_GHC_HR;

        SPIN_UNTIL(!(hba_state.base[AHCI_HBA_GHC] & AHCI_HBA_GHC_HR),
                RESET_DELAY);

        if (hba_state.base[AHCI_HBA_GHC] & AHCI_HBA_GHC_HR)
                panic("unable to reset HBA");
}

/*===========================================================================*
 *                              ahci_init                                    *
 *===========================================================================*/
static void ahci_init(int devind)
{
        /* Initialize the device.
         */
        u32_t base, size, cap, ghc, mask;
        int r, port, ioflag;

        if ((r = pci_get_bar(devind, PCI_BAR_6, &base, &size, &ioflag)) != OK)
                panic("unable to retrieve BAR: %d", r);

        if (ioflag)
                panic("invalid BAR type");

        /* There must be at least one port, and at most NR_PORTS ports. Limit
         * the actual total number of ports to the size of the exposed area.
         */
        if (size < AHCI_MEM_BASE_SIZE + AHCI_MEM_PORT_SIZE)
                panic("HBA memory size too small: %lu", size);

        size = MIN(size, AHCI_MEM_BASE_SIZE + AHCI_MEM_PORT_SIZE * NR_PORTS);

        hba_state.nr_ports = (size - AHCI_MEM_BASE_SIZE) / AHCI_MEM_PORT_SIZE;

        /* Map the register area into local memory. */
        hba_state.base = (u32_t *) vm_map_phys(SELF, (void *) base, size);
        hba_state.size = size;
        if (hba_state.base == MAP_FAILED)
                panic("unable to map HBA memory");

        /* Retrieve, allocate and enable the controller's IRQ. */
        hba_state.irq = pci_attr_r8(devind, PCI_ILR);
        hba_state.hook_id = 0;

        if ((r = sys_irqsetpolicy(hba_state.irq, 0, &hba_state.hook_id)) != OK)
                panic("unable to register IRQ: %d", r);

        if ((r = sys_irqenable(&hba_state.hook_id)) != OK)
                panic("unable to enable IRQ: %d", r);

        /* Reset the HBA. */
        ahci_reset();

        /* Enable AHCI and interrupts. */
        ghc = hba_state.base[AHCI_HBA_GHC];
        hba_state.base[AHCI_HBA_GHC] = ghc | AHCI_HBA_GHC_AE | AHCI_HBA_GHC_IE;

        /* Limit the maximum number of commands to the controller's value. */
        /* Note that we currently use only one command anyway. */
        cap = hba_state.base[AHCI_HBA_CAP];
        hba_state.has_ncq = !!(cap & AHCI_HBA_CAP_SNCQ);
        hba_state.nr_cmds = MIN(NR_CMDS,
                ((cap >> AHCI_HBA_CAP_NCS_SHIFT) & AHCI_HBA_CAP_NCS_MASK) + 1);

        dprintf(V_INFO, ("AHCI%u: HBA v%d.%d%d, %ld ports, %ld commands, "
                "%s queuing, IRQ %d\n",
                ahci_instance,
                (int) (hba_state.base[AHCI_HBA_VS] >> 16),
                (int) ((hba_state.base[AHCI_HBA_VS] >> 8) & 0xFF),
                (int) (hba_state.base[AHCI_HBA_VS] & 0xFF),
                ((cap >> AHCI_HBA_CAP_NP_SHIFT) & AHCI_HBA_CAP_NP_MASK) + 1,
                ((cap >> AHCI_HBA_CAP_NCS_SHIFT) & AHCI_HBA_CAP_NCS_MASK) + 1,
                hba_state.has_ncq ? "supports" : "no", hba_state.irq));

        dprintf(V_INFO, ("AHCI%u: CAP %08x, CAP2 %08x, PI %08x\n",
                ahci_instance, cap, hba_state.base[AHCI_HBA_CAP2],
                hba_state.base[AHCI_HBA_PI]));

        /* Initialize each of the implemented ports. We ignore CAP.NP. */
        mask = hba_state.base[AHCI_HBA_PI];

        for (port = 0; port < hba_state.nr_ports; port++) {
                port_state[port].device = NO_DEVICE;
                port_state[port].state = STATE_NO_PORT;

                if (mask & (1 << port))
                        port_init(&port_state[port]);
        }
}

/*===========================================================================*
 *                              ahci_stop                                    *
 *===========================================================================*/
static void ahci_stop(void)
{
        /* Disable AHCI, and clean up resources to the extent possible.
         */
        struct port_state *ps;
        int r, port;

        for (port = 0; port < hba_state.nr_ports; port++) {
                ps = &port_state[port];

                if (ps->state != STATE_NO_PORT) {
                        port_stop(ps);

                        port_free(ps);
                }
        }

        ahci_reset();

        if ((r = vm_unmap_phys(SELF, (void *) hba_state.base,
                        hba_state.size)) != OK)
                panic("unable to unmap HBA memory: %d", r);

        if ((r = sys_irqrmpolicy(&hba_state.hook_id)) != OK)
                panic("unable to deregister IRQ: %d", r);
}

/*===========================================================================*
 *                              ahci_alarm                                   *
 *===========================================================================*/
static void ahci_alarm(clock_t stamp)
{
        /* Process an alarm.
         */

        /* Call the port-specific handler for each port that timed out. */
        expire_timers(stamp);
}

/*===========================================================================*
 *                              ahci_intr                                    *
 *===========================================================================*/
static void ahci_intr(unsigned int UNUSED(mask))
{
        /* Process an interrupt.
         */
        struct port_state *ps;
        u32_t mask;
        int r, port;

        /* Handle an interrupt for each port that has the interrupt bit set. */
        mask = hba_state.base[AHCI_HBA_IS];

        for (port = 0; port < hba_state.nr_ports; port++) {
                if (mask & (1 << port)) {
                        ps = &port_state[port];

                        port_intr(ps);

                        /* After processing an interrupt, wake up the device
                         * thread if it is suspended and now no longer busy.
                         */
                        if ((ps->flags & (FLAG_SUSPENDED | FLAG_BUSY)) ==
                                        FLAG_SUSPENDED)
                                blockdriver_mt_wakeup(ps->cmd_info[0].tid);
                }
        }

        /* Clear the bits that we processed. */
        hba_state.base[AHCI_HBA_IS] = mask;

        /* Reenable the interrupt. */
        if ((r = sys_irqenable(&hba_state.hook_id)) != OK)
                panic("unable to enable IRQ: %d", r);
}

/*===========================================================================*
 *                              ahci_get_var                                 *
 *===========================================================================*/
static void ahci_get_var(char *name, long *v, int timeout)
{
        /* Retrieve an environment variable, and optionall adjust it to the
         * scale that we are using internally.
         */

        /* The value is supposed to be initialized to a default already. */
        (void) env_parse(name, "d", 0, v, 1, LONG_MAX);

        /* If this is a timeout, convert from milliseconds to ticks. */
        if (timeout)
                *v = (*v + 500) * sys_hz() / 1000;
}

/*===========================================================================*
 *                              ahci_get_params                              *
 *===========================================================================*/
static void ahci_get_params(void)
{
        /* Retrieve and parse parameters passed to this driver, except the
         * device-to-port mapping, which has to be parsed later.
         */
        long v;

        /* Find out which driver instance we are. */
        v = 0;
        (void) env_parse("instance", "d", 0, &v, 0, 255);
        ahci_instance = (int) v;

        /* Initialize the verbosity level. */
        v = V_ERR;
        (void) env_parse("ahci_verbose", "d", 0, &v, V_NONE, V_REQ);
        ahci_verbose = (int) v;

        /* Initialize timeout-related values. */
        ahci_get_var("ahci_init_timeout", &ahci_spinup_timeout, TRUE);
        ahci_get_var("ahci_sig_timeout", &ahci_sig_timeout, TRUE);
        ahci_get_var("ahci_sig_checks", &ahci_sig_checks, FALSE);
        ahci_get_var("ahci_cmd_timeout", &ahci_command_timeout, TRUE);
        ahci_get_var("ahci_io_timeout", &ahci_transfer_timeout, TRUE);
        ahci_get_var("ahci_flush_timeout", &ahci_flush_timeout, TRUE);
}

/*===========================================================================*
 *                              ahci_set_mapping                             *
 *===========================================================================*/
static void ahci_set_mapping(void)
{
        /* Construct a mapping from device nodes to port numbers.
         */
        char key[16], val[32], *p;
        unsigned int port;
        int i, j;

        /* Start off with a mapping that includes implemented ports only, in
         * order. We choose this mapping over an identity mapping to maximize
         * the chance that the user will be able to access the first MAX_DRIVES
         * devices. Note that we can only do this after initializing the HBA.
         */
        for (i = j = 0; i < NR_PORTS && j < MAX_DRIVES; i++)
                if (port_state[i].state != STATE_NO_PORT)
                        ahci_map[j++] = i;

        for ( ; j < MAX_DRIVES; j++)
                ahci_map[j] = NO_PORT;

        /* See if the user specified a custom mapping. Unlike all other
         * configuration options, this is a per-instance setting.
         */
        strlcpy(key, "ahci0_map", sizeof(key));
        key[4] += ahci_instance;

        if (env_get_param(key, val, sizeof(val)) == OK) {
                /* Parse the mapping, which is assumed to be a comma-separated
                 * list of zero-based port numbers.
                 */
                p = val;

                for (i = 0; i < MAX_DRIVES; i++) {
                        if (*p) {
                                port = (unsigned int) strtoul(p, &p, 0);

                                if (*p) p++;

                                ahci_map[i] = port % NR_PORTS;
                        }
                        else ahci_map[i] = NO_PORT;
                }
        }

        /* Create a reverse mapping. */
        for (i = 0; i < MAX_DRIVES; i++)
                if ((j = ahci_map[i]) != NO_PORT)
                        port_state[j].device = i;
}

/*===========================================================================*
 *                              sef_cb_init_fresh                            *
 *===========================================================================*/
static int sef_cb_init_fresh(int type, sef_init_info_t *UNUSED(info))
{
        /* Initialize the driver.
         */
        int devind;

        /* Get command line parameters. */
        ahci_get_params();

        /* Probe for recognized devices, skipping matches as appropriate. */
        devind = ahci_probe(ahci_instance);

        if (devind < 0)
                panic("no matching device found");

        /* Initialize the device we found. */
        ahci_init(devind);

        /* Create a mapping from device nodes to port numbers. */
        ahci_set_mapping();

        /* Announce that we are up. */
        blockdriver_announce(type);

        return OK;
}

/*===========================================================================*
 *                              sef_cb_signal_handler                        *
 *===========================================================================*/
static void sef_cb_signal_handler(int signo)
{
        /* In case of a termination signal, shut down this driver.
         */
        int port;

        if (signo != SIGTERM) return;

        /* If any ports are still opened, assume that the system is being shut
         * down, and stay up until the last device has been closed.
         */
        ahci_exiting = TRUE;

        for (port = 0; port < hba_state.nr_ports; port++)
                if (port_state[port].open_count > 0)
                        return;

        /* If not, stop the driver and exit immediately. */
        ahci_stop();

        exit(0);
}

/*===========================================================================*
 *                              sef_local_startup                            *
 *===========================================================================*/
static void sef_local_startup(void)
{
        /* Set callbacks and initialize the System Event Framework (SEF).
         */

        /* Register init callbacks. */
        sef_setcb_init_fresh(sef_cb_init_fresh);
        sef_setcb_init_lu(sef_cb_init_fresh);

        /* Register signal callbacks. */
        sef_setcb_signal_handler(sef_cb_signal_handler);

        /* Let SEF perform startup. */
        sef_startup();
}

/*===========================================================================*
 *                              ahci_portname                                *
 *===========================================================================*/
static char *ahci_portname(struct port_state *ps)
{
        /* Return a printable name for the given port. Whenever we can, print a
         * "Dx" device number rather than a "Pxx" port number, because the user
         * may not be aware of the mapping currently in use.
         */
        static char name[] = "AHCI0-P00";

        name[4] = '0' + ahci_instance;

        if (ps->device == NO_DEVICE) {
                name[6] = 'P';
                name[7] = '0' + (ps - port_state) / 10;
                name[8] = '0' + (ps - port_state) % 10;
        }
        else {
                name[6] = 'D';
                name[7] = '0' + ps->device;
                name[8] = 0;
        }

        return name;
}

/*===========================================================================*
 *                              ahci_map_minor                               *
 *===========================================================================*/
static struct port_state *ahci_map_minor(dev_t minor, struct device **dvp)
{
        /* Map a minor device number to a port and a pointer to the partition's
         * device structure. Return NULL if this minor device number does not
         * identify an actual device.
         */
        struct port_state *ps;
        int port;

        ps = NULL;

        if (minor < NR_MINORS) {
                port = ahci_map[minor / DEV_PER_DRIVE];

                if (port == NO_PORT)
                        return NULL;

                ps = &port_state[port];
                *dvp = &ps->part[minor % DEV_PER_DRIVE];
        }
        else if ((unsigned) (minor -= MINOR_d0p0s0) < NR_SUBDEVS) {
                port = ahci_map[minor / SUB_PER_DRIVE];

                if (port == NO_PORT)
                        return NULL;

                ps = &port_state[port];
                *dvp = &ps->subpart[minor % SUB_PER_DRIVE];
        }

        return ps;
}

/*===========================================================================*
 *                              ahci_part                                    *
 *===========================================================================*/
static struct device *ahci_part(dev_t minor)
{
        /* Return a pointer to the partition information structure of the given
         * minor device.
         */
        struct device *dv;

        if (ahci_map_minor(minor, &dv) == NULL)
                return NULL;

        return dv;
}

/*===========================================================================*
 *                              ahci_open                                    *
 *===========================================================================*/
static int ahci_open(dev_t minor, int access)
{
        /* Open a device.
         */
        struct port_state *ps;
        int r;

        ps = ahci_get_port(minor);

        /* Only one open request can be processed at a time, due to the fact
         * that it is an exclusive operation. The thread that handles this call
         * can therefore freely register itself at slot zero.
         */
        ps->cmd_info[0].tid = blockdriver_mt_get_tid();

        /* If we are still in the process of initializing this port or device,
         * wait for completion of that phase first.
         */
        if (ps->flags & FLAG_BUSY)
                port_wait(ps);

        /* The device may only be opened if it is now properly functioning. */
        if (ps->state != STATE_GOOD_DEV)
                return ENXIO;

        /* Some devices may only be opened in read-only mode. */
        if ((ps->flags & FLAG_READONLY) && (access & W_BIT))
                return EACCES;

        if (ps->open_count == 0) {
                /* The first open request. Clear the barrier flag, if set. */
                ps->flags &= ~FLAG_BARRIER;

                /* Recheck media only when nobody is using the device. */
                if ((ps->flags & FLAG_ATAPI) &&
                        (r = atapi_check_medium(ps, 0)) != OK)
                        return r;

                /* After rechecking the media, the partition table must always
                 * be read. This is also a convenient time to do it for
                 * nonremovable devices. Start by resetting the partition
                 * tables and setting the working size of the entire device.
                 */
                memset(ps->part, 0, sizeof(ps->part));
                memset(ps->subpart, 0, sizeof(ps->subpart));

                ps->part[0].dv_size =
                        mul64(ps->lba_count, cvu64(ps->sector_size));

                partition(&ahci_dtab, ps->device * DEV_PER_DRIVE, P_PRIMARY,
                        !!(ps->flags & FLAG_ATAPI));

                blockdriver_mt_set_workers(ps->device, ps->queue_depth);
        }
        else {
                /* If the barrier flag is set, deny new open requests until the
                 * device is fully closed first.
                 */
                if (ps->flags & FLAG_BARRIER)
                        return ENXIO;
        }

        ps->open_count++;

        return OK;
}

/*===========================================================================*
 *                              ahci_close                                   *
 *===========================================================================*/
static int ahci_close(dev_t minor)
{
        /* Close a device.
         */
        struct port_state *ps;
        int port;

        ps = ahci_get_port(minor);

        /* Decrease the open count. */
        if (ps->open_count <= 0) {
                dprintf(V_ERR, ("%s: closing already-closed port\n",
                        ahci_portname(ps)));

                return EINVAL;
        }

        ps->open_count--;

        if (ps->open_count > 0)
                return OK;

        /* The device is now fully closed. That also means that the threads for
         * this device are not needed anymore, so we reduce the count to one.
         */
        blockdriver_mt_set_workers(ps->device, 1);

        if (ps->state == STATE_GOOD_DEV && !(ps->flags & FLAG_BARRIER)) {
                dprintf(V_INFO, ("%s: flushing write cache\n",
                        ahci_portname(ps)));

                (void) gen_flush_wcache(ps);
        }

        /* If the entire driver has been told to terminate, check whether all
         * devices are now closed. If so, tell libblockdriver to quit after
         * replying to the close request.
         */
        if (ahci_exiting) {
                for (port = 0; port < hba_state.nr_ports; port++)
                        if (port_state[port].open_count > 0)
                                break;

                if (port == hba_state.nr_ports) {
                        ahci_stop();

                        blockdriver_mt_terminate();
                }
        }

        return OK;
}

/*===========================================================================*
 *                              ahci_transfer                                *
 *===========================================================================*/
static ssize_t ahci_transfer(dev_t minor, int do_write, u64_t position,
        endpoint_t endpt, iovec_t *iovec, unsigned int count, int flags)
{
        /* Perform data transfer on the selected device.
         */
        struct port_state *ps;
        struct device *dv;
        u64_t pos, eof;

        ps = ahci_get_port(minor);
        dv = ahci_part(minor);

        if (ps->state != STATE_GOOD_DEV || (ps->flags & FLAG_BARRIER))
                return EIO;

        if (count > NR_IOREQS)
                return EINVAL;

        /* Check for basic end-of-partition condition: if the start position of
         * the request is outside the partition, return success immediately.
         * The size of the request is obtained, and possibly reduced, later.
         */
        if (cmp64(position, dv->dv_size) >= 0)
                return OK;

        pos = add64(dv->dv_base, position);
        eof = add64(dv->dv_base, dv->dv_size);

        return port_transfer(ps, pos, eof, endpt, (iovec_s_t *) iovec, count,
                do_write, flags);
}

/*===========================================================================*
 *                              ahci_ioctl                                   *
 *===========================================================================*/
static int ahci_ioctl(dev_t minor, unsigned int request, endpoint_t endpt,
        cp_grant_id_t grant)
{
        /* Process I/O control requests.
         */
        struct port_state *ps;
        int r, val;

        ps = ahci_get_port(minor);

        switch (request) {
        case DIOCEJECT:
                if (ps->state != STATE_GOOD_DEV || (ps->flags & FLAG_BARRIER))
                        return EIO;

                if (!(ps->flags & FLAG_ATAPI))
                        return EINVAL;

                return atapi_load_eject(ps, 0, FALSE /*load*/);

        case DIOCOPENCT:
                return sys_safecopyto(endpt, grant, 0,
                        (vir_bytes) &ps->open_count, sizeof(ps->open_count));

        case DIOCFLUSH:
                if (ps->state != STATE_GOOD_DEV || (ps->flags & FLAG_BARRIER))
                        return EIO;

                return gen_flush_wcache(ps);

        case DIOCSETWC:
                if (ps->state != STATE_GOOD_DEV || (ps->flags & FLAG_BARRIER))
                        return EIO;

                if ((r = sys_safecopyfrom(endpt, grant, 0, (vir_bytes) &val,
                        sizeof(val))) != OK)
                        return r;

                return gen_set_wcache(ps, val);

        case DIOCGETWC:
                if (ps->state != STATE_GOOD_DEV || (ps->flags & FLAG_BARRIER))
                        return EIO;

                if ((r = gen_get_wcache(ps, &val)) != OK)
                        return r;

                return sys_safecopyto(endpt, grant, 0, (vir_bytes) &val,
                        sizeof(val));
        }

        return EINVAL;
}

/*===========================================================================*
 *                              ahci_device                                  *
 *===========================================================================*/
static int ahci_device(dev_t minor, device_id_t *id)
{
        /* Map a minor device number to a device ID.
         */
        struct port_state *ps;
        struct device *dv;

        if ((ps = ahci_map_minor(minor, &dv)) == NULL)
                return ENXIO;

        *id = ps->device;

        return OK;
}

/*===========================================================================*
 *                              ahci_get_port                                *
 *===========================================================================*/
static struct port_state *ahci_get_port(dev_t minor)
{
        /* Get the port structure associated with the given minor device.
         * Called only from worker threads, so the minor device is already
         * guaranteed to map to a port.
         */
        struct port_state *ps;
        struct device *dv;

        if ((ps = ahci_map_minor(minor, &dv)) == NULL)
                panic("device mapping for minor %d disappeared", minor);

        return ps;
}

/*===========================================================================*
 *                              main                                         *
 *===========================================================================*/
int main(int argc, char **argv)
{
        /* Driver task.
         */

        env_setargs(argc, argv);
        sef_local_startup();

        blockdriver_mt_task(&ahci_dtab);

        return 0;
}