treewide: remove redundant IS_ERR() before error code check

[linux/fpc-iii.git] / drivers / infiniband / hw / qib / qib_diag.c

/*
 * Copyright (c) 2012 Intel Corporation. All rights reserved.
 * Copyright (c) 2006 - 2012 QLogic Corporation. All rights reserved.
 * Copyright (c) 2003, 2004, 2005, 2006 PathScale, Inc. All rights reserved.
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * OpenIB.org BSD license below:
 *
 *     Redistribution and use in source and binary forms, with or
 *     without modification, are permitted provided that the following
 *     conditions are met:
 *
 *      - Redistributions of source code must retain the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer.
 *
 *      - Redistributions in binary form must reproduce the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer in the documentation and/or other materials
 *        provided with the distribution.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

/*
 * This file contains support for diagnostic functions.  It is accessed by
 * opening the qib_diag device, normally minor number 129.  Diagnostic use
 * of the QLogic_IB chip may render the chip or board unusable until the
 * driver is unloaded, or in some cases, until the system is rebooted.
 *
 * Accesses to the chip through this interface are not similar to going
 * through the /sys/bus/pci resource mmap interface.
 */

#include <linux/io.h>
#include <linux/pci.h>
#include <linux/poll.h>
#include <linux/vmalloc.h>
#include <linux/export.h>
#include <linux/fs.h>
#include <linux/uaccess.h>

#include "qib.h"
#include "qib_common.h"

#undef pr_fmt
#define pr_fmt(fmt) QIB_DRV_NAME ": " fmt

/*
 * Each client that opens the diag device must read then write
 * offset 0, to prevent lossage from random cat or od. diag_state
 * sequences this "handshake".
 */
enum diag_state { UNUSED = 0, OPENED, INIT, READY };

/* State for an individual client. PID so children cannot abuse handshake */
static struct qib_diag_client {
        struct qib_diag_client *next;
        struct qib_devdata *dd;
        pid_t pid;
        enum diag_state state;
} *client_pool;

/*
 * Get a client struct. Recycled if possible, else kmalloc.
 * Must be called with qib_mutex held
 */
static struct qib_diag_client *get_client(struct qib_devdata *dd)
{
        struct qib_diag_client *dc;

        dc = client_pool;
        if (dc)
                /* got from pool remove it and use */
                client_pool = dc->next;
        else
                /* None in pool, alloc and init */
                dc = kmalloc(sizeof(*dc), GFP_KERNEL);

        if (dc) {
                dc->next = NULL;
                dc->dd = dd;
                dc->pid = current->pid;
                dc->state = OPENED;
        }
        return dc;
}

/*
 * Return to pool. Must be called with qib_mutex held
 */
static void return_client(struct qib_diag_client *dc)
{
        struct qib_devdata *dd = dc->dd;
        struct qib_diag_client *tdc, *rdc;

        rdc = NULL;
        if (dc == dd->diag_client) {
                dd->diag_client = dc->next;
                rdc = dc;
        } else {
                tdc = dc->dd->diag_client;
                while (tdc) {
                        if (dc == tdc->next) {
                                tdc->next = dc->next;
                                rdc = dc;
                                break;
                        }
                        tdc = tdc->next;
                }
        }
        if (rdc) {
                rdc->state = UNUSED;
                rdc->dd = NULL;
                rdc->pid = 0;
                rdc->next = client_pool;
                client_pool = rdc;
        }
}

static int qib_diag_open(struct inode *in, struct file *fp);
static int qib_diag_release(struct inode *in, struct file *fp);
static ssize_t qib_diag_read(struct file *fp, char __user *data,
                             size_t count, loff_t *off);
static ssize_t qib_diag_write(struct file *fp, const char __user *data,
                              size_t count, loff_t *off);

static const struct file_operations diag_file_ops = {
        .owner = THIS_MODULE,
        .write = qib_diag_write,
        .read = qib_diag_read,
        .open = qib_diag_open,
        .release = qib_diag_release,
        .llseek = default_llseek,
};

static atomic_t diagpkt_count = ATOMIC_INIT(0);
static struct cdev *diagpkt_cdev;
static struct device *diagpkt_device;

static ssize_t qib_diagpkt_write(struct file *fp, const char __user *data,
                                 size_t count, loff_t *off);

static const struct file_operations diagpkt_file_ops = {
        .owner = THIS_MODULE,
        .write = qib_diagpkt_write,
        .llseek = noop_llseek,
};

int qib_diag_add(struct qib_devdata *dd)
{
        char name[16];
        int ret = 0;

        if (atomic_inc_return(&diagpkt_count) == 1) {
                ret = qib_cdev_init(QIB_DIAGPKT_MINOR, "ipath_diagpkt",
                                    &diagpkt_file_ops, &diagpkt_cdev,
                                    &diagpkt_device);
                if (ret)
                        goto done;
        }

        snprintf(name, sizeof(name), "ipath_diag%d", dd->unit);
        ret = qib_cdev_init(QIB_DIAG_MINOR_BASE + dd->unit, name,
                            &diag_file_ops, &dd->diag_cdev,
                            &dd->diag_device);
done:
        return ret;
}

static void qib_unregister_observers(struct qib_devdata *dd);

void qib_diag_remove(struct qib_devdata *dd)
{
        struct qib_diag_client *dc;

        if (atomic_dec_and_test(&diagpkt_count))
                qib_cdev_cleanup(&diagpkt_cdev, &diagpkt_device);

        qib_cdev_cleanup(&dd->diag_cdev, &dd->diag_device);

        /*
         * Return all diag_clients of this device. There should be none,
         * as we are "guaranteed" that no clients are still open
         */
        while (dd->diag_client)
                return_client(dd->diag_client);

        /* Now clean up all unused client structs */
        while (client_pool) {
                dc = client_pool;
                client_pool = dc->next;
                kfree(dc);
        }
        /* Clean up observer list */
        qib_unregister_observers(dd);
}

/* qib_remap_ioaddr32 - remap an offset into chip address space to __iomem *
 *
 * @dd: the qlogic_ib device
 * @offs: the offset in chip-space
 * @cntp: Pointer to max (byte) count for transfer starting at offset
 * This returns a u32 __iomem * so it can be used for both 64 and 32-bit
 * mapping. It is needed because with the use of PAT for control of
 * write-combining, the logically contiguous address-space of the chip
 * may be split into virtually non-contiguous spaces, with different
 * attributes, which are them mapped to contiguous physical space
 * based from the first BAR.
 *
 * The code below makes the same assumptions as were made in
 * init_chip_wc_pat() (qib_init.c), copied here:
 * Assumes chip address space looks like:
 *              - kregs + sregs + cregs + uregs (in any order)
 *              - piobufs (2K and 4K bufs in either order)
 *      or:
 *              - kregs + sregs + cregs (in any order)
 *              - piobufs (2K and 4K bufs in either order)
 *              - uregs
 *
 * If cntp is non-NULL, returns how many bytes from offset can be accessed
 * Returns 0 if the offset is not mapped.
 */
static u32 __iomem *qib_remap_ioaddr32(struct qib_devdata *dd, u32 offset,
                                       u32 *cntp)
{
        u32 kreglen;
        u32 snd_bottom, snd_lim = 0;
        u32 __iomem *krb32 = (u32 __iomem *)dd->kregbase;
        u32 __iomem *map = NULL;
        u32 cnt = 0;
        u32 tot4k, offs4k;

        /* First, simplest case, offset is within the first map. */
        kreglen = (dd->kregend - dd->kregbase) * sizeof(u64);
        if (offset < kreglen) {
                map = krb32 + (offset / sizeof(u32));
                cnt = kreglen - offset;
                goto mapped;
        }

        /*
         * Next check for user regs, the next most common case,
         * and a cheap check because if they are not in the first map
         * they are last in chip.
         */
        if (dd->userbase) {
                /* If user regs mapped, they are after send, so set limit. */
                u32 ulim = (dd->cfgctxts * dd->ureg_align) + dd->uregbase;

                if (!dd->piovl15base)
                        snd_lim = dd->uregbase;
                krb32 = (u32 __iomem *)dd->userbase;
                if (offset >= dd->uregbase && offset < ulim) {
                        map = krb32 + (offset - dd->uregbase) / sizeof(u32);
                        cnt = ulim - offset;
                        goto mapped;
                }
        }

        /*
         * Lastly, check for offset within Send Buffers.
         * This is gnarly because struct devdata is deliberately vague
         * about things like 7322 VL15 buffers, and we are not in
         * chip-specific code here, so should not make many assumptions.
         * The one we _do_ make is that the only chip that has more sndbufs
         * than we admit is the 7322, and it has userregs above that, so
         * we know the snd_lim.
         */
        /* Assume 2K buffers are first. */
        snd_bottom = dd->pio2k_bufbase;
        if (snd_lim == 0) {
                u32 tot2k = dd->piobcnt2k * ALIGN(dd->piosize2k, dd->palign);

                snd_lim = snd_bottom + tot2k;
        }
        /* If 4k buffers exist, account for them by bumping
         * appropriate limit.
         */
        tot4k = dd->piobcnt4k * dd->align4k;
        offs4k = dd->piobufbase >> 32;
        if (dd->piobcnt4k) {
                if (snd_bottom > offs4k)
                        snd_bottom = offs4k;
                else {
                        /* 4k above 2k. Bump snd_lim, if needed*/
                        if (!dd->userbase || dd->piovl15base)
                                snd_lim = offs4k + tot4k;
                }
        }
        /*
         * Judgement call: can we ignore the space between SendBuffs and
         * UserRegs, where we would like to see vl15 buffs, but not more?
         */
        if (offset >= snd_bottom && offset < snd_lim) {
                offset -= snd_bottom;
                map = (u32 __iomem *)dd->piobase + (offset / sizeof(u32));
                cnt = snd_lim - offset;
        }

        if (!map && offs4k && dd->piovl15base) {
                snd_lim = offs4k + tot4k + 2 * dd->align4k;
                if (offset >= (offs4k + tot4k) && offset < snd_lim) {
                        map = (u32 __iomem *)dd->piovl15base +
                                ((offset - (offs4k + tot4k)) / sizeof(u32));
                        cnt = snd_lim - offset;
                }
        }

mapped:
        if (cntp)
                *cntp = cnt;
        return map;
}

/*
 * qib_read_umem64 - read a 64-bit quantity from the chip into user space
 * @dd: the qlogic_ib device
 * @uaddr: the location to store the data in user memory
 * @regoffs: the offset from BAR0 (_NOT_ full pointer, anymore)
 * @count: number of bytes to copy (multiple of 32 bits)
 *
 * This function also localizes all chip memory accesses.
 * The copy should be written such that we read full cacheline packets
 * from the chip.  This is usually used for a single qword
 *
 * NOTE:  This assumes the chip address is 64-bit aligned.
 */
static int qib_read_umem64(struct qib_devdata *dd, void __user *uaddr,
                           u32 regoffs, size_t count)
{
        const u64 __iomem *reg_addr;
        const u64 __iomem *reg_end;
        u32 limit;
        int ret;

        reg_addr = (const u64 __iomem *)qib_remap_ioaddr32(dd, regoffs, &limit);
        if (reg_addr == NULL || limit == 0 || !(dd->flags & QIB_PRESENT)) {
                ret = -EINVAL;
                goto bail;
        }
        if (count >= limit)
                count = limit;
        reg_end = reg_addr + (count / sizeof(u64));

        /* not very efficient, but it works for now */
        while (reg_addr < reg_end) {
                u64 data = readq(reg_addr);

                if (copy_to_user(uaddr, &data, sizeof(u64))) {
                        ret = -EFAULT;
                        goto bail;
                }
                reg_addr++;
                uaddr += sizeof(u64);
        }
        ret = 0;
bail:
        return ret;
}

/*
 * qib_write_umem64 - write a 64-bit quantity to the chip from user space
 * @dd: the qlogic_ib device
 * @regoffs: the offset from BAR0 (_NOT_ full pointer, anymore)
 * @uaddr: the source of the data in user memory
 * @count: the number of bytes to copy (multiple of 32 bits)
 *
 * This is usually used for a single qword
 * NOTE:  This assumes the chip address is 64-bit aligned.
 */

static int qib_write_umem64(struct qib_devdata *dd, u32 regoffs,
                            const void __user *uaddr, size_t count)
{
        u64 __iomem *reg_addr;
        const u64 __iomem *reg_end;
        u32 limit;
        int ret;

        reg_addr = (u64 __iomem *)qib_remap_ioaddr32(dd, regoffs, &limit);
        if (reg_addr == NULL || limit == 0 || !(dd->flags & QIB_PRESENT)) {
                ret = -EINVAL;
                goto bail;
        }
        if (count >= limit)
                count = limit;
        reg_end = reg_addr + (count / sizeof(u64));

        /* not very efficient, but it works for now */
        while (reg_addr < reg_end) {
                u64 data;

                if (copy_from_user(&data, uaddr, sizeof(data))) {
                        ret = -EFAULT;
                        goto bail;
                }
                writeq(data, reg_addr);

                reg_addr++;
                uaddr += sizeof(u64);
        }
        ret = 0;
bail:
        return ret;
}

/*
 * qib_read_umem32 - read a 32-bit quantity from the chip into user space
 * @dd: the qlogic_ib device
 * @uaddr: the location to store the data in user memory
 * @regoffs: the offset from BAR0 (_NOT_ full pointer, anymore)
 * @count: number of bytes to copy
 *
 * read 32 bit values, not 64 bit; for memories that only
 * support 32 bit reads; usually a single dword.
 */
static int qib_read_umem32(struct qib_devdata *dd, void __user *uaddr,
                           u32 regoffs, size_t count)
{
        const u32 __iomem *reg_addr;
        const u32 __iomem *reg_end;
        u32 limit;
        int ret;

        reg_addr = qib_remap_ioaddr32(dd, regoffs, &limit);
        if (reg_addr == NULL || limit == 0 || !(dd->flags & QIB_PRESENT)) {
                ret = -EINVAL;
                goto bail;
        }
        if (count >= limit)
                count = limit;
        reg_end = reg_addr + (count / sizeof(u32));

        /* not very efficient, but it works for now */
        while (reg_addr < reg_end) {
                u32 data = readl(reg_addr);

                if (copy_to_user(uaddr, &data, sizeof(data))) {
                        ret = -EFAULT;
                        goto bail;
                }

                reg_addr++;
                uaddr += sizeof(u32);

        }
        ret = 0;
bail:
        return ret;
}

/*
 * qib_write_umem32 - write a 32-bit quantity to the chip from user space
 * @dd: the qlogic_ib device
 * @regoffs: the offset from BAR0 (_NOT_ full pointer, anymore)
 * @uaddr: the source of the data in user memory
 * @count: number of bytes to copy
 *
 * write 32 bit values, not 64 bit; for memories that only
 * support 32 bit write; usually a single dword.
 */

static int qib_write_umem32(struct qib_devdata *dd, u32 regoffs,
                            const void __user *uaddr, size_t count)
{
        u32 __iomem *reg_addr;
        const u32 __iomem *reg_end;
        u32 limit;
        int ret;

        reg_addr = qib_remap_ioaddr32(dd, regoffs, &limit);
        if (reg_addr == NULL || limit == 0 || !(dd->flags & QIB_PRESENT)) {
                ret = -EINVAL;
                goto bail;
        }
        if (count >= limit)
                count = limit;
        reg_end = reg_addr + (count / sizeof(u32));

        while (reg_addr < reg_end) {
                u32 data;

                if (copy_from_user(&data, uaddr, sizeof(data))) {
                        ret = -EFAULT;
                        goto bail;
                }
                writel(data, reg_addr);

                reg_addr++;
                uaddr += sizeof(u32);
        }
        ret = 0;
bail:
        return ret;
}

static int qib_diag_open(struct inode *in, struct file *fp)
{
        int unit = iminor(in) - QIB_DIAG_MINOR_BASE;
        struct qib_devdata *dd;
        struct qib_diag_client *dc;
        int ret;

        mutex_lock(&qib_mutex);

        dd = qib_lookup(unit);

        if (dd == NULL || !(dd->flags & QIB_PRESENT) ||
            !dd->kregbase) {
                ret = -ENODEV;
                goto bail;
        }

        dc = get_client(dd);
        if (!dc) {
                ret = -ENOMEM;
                goto bail;
        }
        dc->next = dd->diag_client;
        dd->diag_client = dc;
        fp->private_data = dc;
        ret = 0;
bail:
        mutex_unlock(&qib_mutex);

        return ret;
}

/**
 * qib_diagpkt_write - write an IB packet
 * @fp: the diag data device file pointer
 * @data: qib_diag_pkt structure saying where to get the packet
 * @count: size of data to write
 * @off: unused by this code
 */
static ssize_t qib_diagpkt_write(struct file *fp,
                                 const char __user *data,
                                 size_t count, loff_t *off)
{
        u32 __iomem *piobuf;
        u32 plen, pbufn, maxlen_reserve;
        struct qib_diag_xpkt dp;
        u32 *tmpbuf = NULL;
        struct qib_devdata *dd;
        struct qib_pportdata *ppd;
        ssize_t ret = 0;

        if (count != sizeof(dp)) {
                ret = -EINVAL;
                goto bail;
        }
        if (copy_from_user(&dp, data, sizeof(dp))) {
                ret = -EFAULT;
                goto bail;
        }

        dd = qib_lookup(dp.unit);
        if (!dd || !(dd->flags & QIB_PRESENT) || !dd->kregbase) {
                ret = -ENODEV;
                goto bail;
        }
        if (!(dd->flags & QIB_INITTED)) {
                /* no hardware, freeze, etc. */
                ret = -ENODEV;
                goto bail;
        }

        if (dp.version != _DIAG_XPKT_VERS) {
                qib_dev_err(dd, "Invalid version %u for diagpkt_write\n",
                            dp.version);
                ret = -EINVAL;
                goto bail;
        }
        /* send count must be an exact number of dwords */
        if (dp.len & 3) {
                ret = -EINVAL;
                goto bail;
        }
        if (!dp.port || dp.port > dd->num_pports) {
                ret = -EINVAL;
                goto bail;
        }
        ppd = &dd->pport[dp.port - 1];

        /*
         * need total length before first word written, plus 2 Dwords. One Dword
         * is for padding so we get the full user data when not aligned on
         * a word boundary. The other Dword is to make sure we have room for the
         * ICRC which gets tacked on later.
         */
        maxlen_reserve = 2 * sizeof(u32);
        if (dp.len > ppd->ibmaxlen - maxlen_reserve) {
                ret = -EINVAL;
                goto bail;
        }

        plen = sizeof(u32) + dp.len;

        tmpbuf = vmalloc(plen);
        if (!tmpbuf) {
                ret = -ENOMEM;
                goto bail;
        }

        if (copy_from_user(tmpbuf,
                           u64_to_user_ptr(dp.data),
                           dp.len)) {
                ret = -EFAULT;
                goto bail;
        }

        plen >>= 2;             /* in dwords */

        if (dp.pbc_wd == 0)
                dp.pbc_wd = plen;

        piobuf = dd->f_getsendbuf(ppd, dp.pbc_wd, &pbufn);
        if (!piobuf) {
                ret = -EBUSY;
                goto bail;
        }
        /* disarm it just to be extra sure */
        dd->f_sendctrl(dd->pport, QIB_SENDCTRL_DISARM_BUF(pbufn));

        /* disable header check on pbufn for this packet */
        dd->f_txchk_change(dd, pbufn, 1, TXCHK_CHG_TYPE_DIS1, NULL);

        writeq(dp.pbc_wd, piobuf);
        /*
         * Copy all but the trigger word, then flush, so it's written
         * to chip before trigger word, then write trigger word, then
         * flush again, so packet is sent.
         */
        if (dd->flags & QIB_PIO_FLUSH_WC) {
                qib_flush_wc();
                qib_pio_copy(piobuf + 2, tmpbuf, plen - 1);
                qib_flush_wc();
                __raw_writel(tmpbuf[plen - 1], piobuf + plen + 1);
        } else
                qib_pio_copy(piobuf + 2, tmpbuf, plen);

        if (dd->flags & QIB_USE_SPCL_TRIG) {
                u32 spcl_off = (pbufn >= dd->piobcnt2k) ? 2047 : 1023;

                qib_flush_wc();
                __raw_writel(0xaebecede, piobuf + spcl_off);
        }

        /*
         * Ensure buffer is written to the chip, then re-enable
         * header checks (if supported by chip).  The txchk
         * code will ensure seen by chip before returning.
         */
        qib_flush_wc();
        qib_sendbuf_done(dd, pbufn);
        dd->f_txchk_change(dd, pbufn, 1, TXCHK_CHG_TYPE_ENAB1, NULL);

        ret = sizeof(dp);

bail:
        vfree(tmpbuf);
        return ret;
}

static int qib_diag_release(struct inode *in, struct file *fp)
{
        mutex_lock(&qib_mutex);
        return_client(fp->private_data);
        fp->private_data = NULL;
        mutex_unlock(&qib_mutex);
        return 0;
}

/*
 * Chip-specific code calls to register its interest in
 * a specific range.
 */
struct diag_observer_list_elt {
        struct diag_observer_list_elt *next;
        const struct diag_observer *op;
};

int qib_register_observer(struct qib_devdata *dd,
                          const struct diag_observer *op)
{
        struct diag_observer_list_elt *olp;
        unsigned long flags;

        if (!dd || !op)
                return -EINVAL;
        olp = vmalloc(sizeof(*olp));
        if (!olp)
                return -ENOMEM;

        spin_lock_irqsave(&dd->qib_diag_trans_lock, flags);
        olp->op = op;
        olp->next = dd->diag_observer_list;
        dd->diag_observer_list = olp;
        spin_unlock_irqrestore(&dd->qib_diag_trans_lock, flags);

        return 0;
}

/* Remove all registered observers when device is closed */
static void qib_unregister_observers(struct qib_devdata *dd)
{
        struct diag_observer_list_elt *olp;
        unsigned long flags;

        spin_lock_irqsave(&dd->qib_diag_trans_lock, flags);
        olp = dd->diag_observer_list;
        while (olp) {
                /* Pop one observer, let go of lock */
                dd->diag_observer_list = olp->next;
                spin_unlock_irqrestore(&dd->qib_diag_trans_lock, flags);
                vfree(olp);
                /* try again. */
                spin_lock_irqsave(&dd->qib_diag_trans_lock, flags);
                olp = dd->diag_observer_list;
        }
        spin_unlock_irqrestore(&dd->qib_diag_trans_lock, flags);
}

/*
 * Find the observer, if any, for the specified address. Initial implementation
 * is simple stack of observers. This must be called with diag transaction
 * lock held.
 */
static const struct diag_observer *diag_get_observer(struct qib_devdata *dd,
                                                     u32 addr)
{
        struct diag_observer_list_elt *olp;
        const struct diag_observer *op = NULL;

        olp = dd->diag_observer_list;
        while (olp) {
                op = olp->op;
                if (addr >= op->bottom && addr <= op->top)
                        break;
                olp = olp->next;
        }
        if (!olp)
                op = NULL;

        return op;
}

static ssize_t qib_diag_read(struct file *fp, char __user *data,
                             size_t count, loff_t *off)
{
        struct qib_diag_client *dc = fp->private_data;
        struct qib_devdata *dd = dc->dd;
        ssize_t ret;

        if (dc->pid != current->pid) {
                ret = -EPERM;
                goto bail;
        }

        if (count == 0)
                ret = 0;
        else if ((count % 4) || (*off % 4))
                /* address or length is not 32-bit aligned, hence invalid */
                ret = -EINVAL;
        else if (dc->state < READY && (*off || count != 8))
                ret = -EINVAL;  /* prevent cat /dev/qib_diag* */
        else {
                unsigned long flags;
                u64 data64 = 0;
                int use_32;
                const struct diag_observer *op;

                use_32 = (count % 8) || (*off % 8);
                ret = -1;
                spin_lock_irqsave(&dd->qib_diag_trans_lock, flags);
                /*
                 * Check for observer on this address range.
                 * we only support a single 32 or 64-bit read
                 * via observer, currently.
                 */
                op = diag_get_observer(dd, *off);
                if (op) {
                        u32 offset = *off;

                        ret = op->hook(dd, op, offset, &data64, 0, use_32);
                }
                /*
                 * We need to release lock before any copy_to_user(),
                 * whether implicit in qib_read_umem* or explicit below.
                 */
                spin_unlock_irqrestore(&dd->qib_diag_trans_lock, flags);
                if (!op) {
                        if (use_32)
                                /*
                                 * Address or length is not 64-bit aligned;
                                 * do 32-bit rd
                                 */
                                ret = qib_read_umem32(dd, data, (u32) *off,
                                                      count);
                        else
                                ret = qib_read_umem64(dd, data, (u32) *off,
                                                      count);
                } else if (ret == count) {
                        /* Below finishes case where observer existed */
                        ret = copy_to_user(data, &data64, use_32 ?
                                           sizeof(u32) : sizeof(u64));
                        if (ret)
                                ret = -EFAULT;
                }
        }

        if (ret >= 0) {
                *off += count;
                ret = count;
                if (dc->state == OPENED)
                        dc->state = INIT;
        }
bail:
        return ret;
}

static ssize_t qib_diag_write(struct file *fp, const char __user *data,
                              size_t count, loff_t *off)
{
        struct qib_diag_client *dc = fp->private_data;
        struct qib_devdata *dd = dc->dd;
        ssize_t ret;

        if (dc->pid != current->pid) {
                ret = -EPERM;
                goto bail;
        }

        if (count == 0)
                ret = 0;
        else if ((count % 4) || (*off % 4))
                /* address or length is not 32-bit aligned, hence invalid */
                ret = -EINVAL;
        else if (dc->state < READY &&
                ((*off || count != 8) || dc->state != INIT))
                /* No writes except second-step of init seq */
                ret = -EINVAL;  /* before any other write allowed */
        else {
                unsigned long flags;
                const struct diag_observer *op = NULL;
                int use_32 =  (count % 8) || (*off % 8);

                /*
                 * Check for observer on this address range.
                 * We only support a single 32 or 64-bit write
                 * via observer, currently. This helps, because
                 * we would otherwise have to jump through hoops
                 * to make "diag transaction" meaningful when we
                 * cannot do a copy_from_user while holding the lock.
                 */
                if (count == 4 || count == 8) {
                        u64 data64;
                        u32 offset = *off;

                        ret = copy_from_user(&data64, data, count);
                        if (ret) {
                                ret = -EFAULT;
                                goto bail;
                        }
                        spin_lock_irqsave(&dd->qib_diag_trans_lock, flags);
                        op = diag_get_observer(dd, *off);
                        if (op)
                                ret = op->hook(dd, op, offset, &data64, ~0Ull,
                                               use_32);
                        spin_unlock_irqrestore(&dd->qib_diag_trans_lock, flags);
                }

                if (!op) {
                        if (use_32)
                                /*
                                 * Address or length is not 64-bit aligned;
                                 * do 32-bit write
                                 */
                                ret = qib_write_umem32(dd, (u32) *off, data,
                                                       count);
                        else
                                ret = qib_write_umem64(dd, (u32) *off, data,
                                                       count);
                }
        }

        if (ret >= 0) {
                *off += count;
                ret = count;
                if (dc->state == INIT)
                        dc->state = READY; /* all read/write OK now */
        }
bail:
        return ret;
}