First Support on Ginger and OMAP TI

[linux-ginger.git] / drivers / staging / altpciechdma / altpciechdma.c

/**
 * Driver for Altera PCIe core chaining DMA reference design.
 *
 * Copyright (C) 2008 Leon Woestenberg  <leon.woestenberg@axon.tv>
 * Copyright (C) 2008 Nickolas Heppermann  <heppermannwdt@gmail.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 *
 * Rationale: This driver exercises the chaining DMA read and write engine
 * in the reference design. It is meant as a complementary reference
 * driver that can be used for testing early designs as well as a basis to
 * write your custom driver.
 *
 * Status: Test results from Leon Woestenberg  <leon.woestenberg@axon.tv>:
 *
 * Sendero Board w/ Cyclone II EP2C35F672C6N, PX1011A PCIe x1 PHY on a
 * Dell Precision 370 PC, x86, kernel 2.6.20 from Ubuntu 7.04.
 *
 * Sendero Board w/ Cyclone II EP2C35F672C6N, PX1011A PCIe x1 PHY on a
 * Freescale MPC8313E-RDB board, PowerPC, 2.6.24 w/ Freescale patches.
 *
 * Driver tests passed with PCIe Compiler 8.1. With PCIe 8.0 the DMA
 * loopback test had reproducable compare errors. I assume a change
 * in the compiler or reference design, but could not find evidence nor
 * documentation on a change or fix in that direction.
 *
 * The reference design does not have readable locations and thus a
 * dummy read, used to flush PCI posted writes, cannot be performed.
 *
 */

#include <linux/kernel.h>
#include <linux/cdev.h>
#include <linux/delay.h>
#include <linux/dma-mapping.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/jiffies.h>
#include <linux/module.h>
#include <linux/pci.h>


/* by default do not build the character device interface */
/* XXX It is non-functional yet */
#ifndef ALTPCIECHDMA_CDEV
#  define ALTPCIECHDMA_CDEV 0
#endif

/* build the character device interface? */
#if ALTPCIECHDMA_CDEV
#  define MAX_CHDMA_SIZE (8 * 1024 * 1024)
#  include "mapper_user_to_sg.h"
#endif

/** driver name, mimicks Altera naming of the reference design */
#define DRV_NAME "altpciechdma"
/** number of BARs on the device */
#define APE_BAR_NUM (6)
/** BAR number where the RCSLAVE memory sits */
#define APE_BAR_RCSLAVE (0)
/** BAR number where the Descriptor Header sits */
#define APE_BAR_HEADER (2)

/** maximum size in bytes of the descriptor table, chdma logic limit */
#define APE_CHDMA_TABLE_SIZE (4096)
/* single transfer must not exceed 255 table entries. worst case this can be
 * achieved by 255 scattered pages, with only a single byte in the head and
 * tail pages. 253 * PAGE_SIZE is a safe upper bound for the transfer size.
 */
#define APE_CHDMA_MAX_TRANSFER_LEN (253 * PAGE_SIZE)

/**
 * Specifies those BARs to be mapped and the length of each mapping.
 *
 * Zero (0) means do not map, otherwise specifies the BAR lengths to be mapped.
 * If the actual BAR length is less, this is considered an error; then
 * reconfigure your PCIe core.
 *
 * @see ug_pci_express 8.0, table 7-2 at page 7-13.
 */
static const unsigned long bar_min_len[APE_BAR_NUM] =
        { 32768, 0, 256, 0, 32768, 0 };

/**
 * Descriptor Header, controls the DMA read engine or write engine.
 *
 * The descriptor header is the main data structure for starting DMA transfers.
 *
 * It sits in End Point (FPGA) memory BAR[2] for 32-bit or BAR[3:2] for 64-bit.
 * It references a descriptor table which exists in Root Complex (PC) memory.
 * Writing the rclast field starts the DMA operation, thus all other structures
 * and fields must be setup before doing so.
 *
 * @see ug_pci_express 8.0, tables 7-3, 7-4 and 7-5 at page 7-14.
 * @note This header must be written in four 32-bit (PCI DWORD) writes.
 */
struct ape_chdma_header {
        /**
         * w0 consists of two 16-bit fields:
         * lsb u16 number; number of descriptors in ape_chdma_table
         * msb u16 control; global control flags
         */
        u32 w0;
        /* bus address to ape_chdma_table in Root Complex memory */
        u32 bdt_addr_h;
        u32 bdt_addr_l;
        /**
         * w3 consists of two 16-bit fields:
         * - lsb u16 rclast; last descriptor number available in Root Complex
         *    - zero (0) means the first descriptor is ready,
         *    - one (1) means two descriptors are ready, etc.
         * - msb u16 reserved;
         *
         * @note writing to this memory location starts the DMA operation!
         */
        u32 w3;
} __attribute__ ((packed));

/**
 * Descriptor Entry, describing a (non-scattered) single memory block transfer.
 *
 * There is one descriptor for each memory block involved in the transfer, a
 * block being a contiguous address range on the bus.
 *
 * Multiple descriptors are chained by means of the ape_chdma_table data
 * structure.
 *
 * @see ug_pci_express 8.0, tables 7-6, 7-7 and 7-8 at page 7-14 and page 7-15.
 */
struct ape_chdma_desc {
        /**
         * w0 consists of two 16-bit fields:
         * number of DWORDS to transfer
         * - lsb u16 length;
         * global control
         * - msb u16 control;
         */
        u32 w0;
        /* address of memory in the End Point */
        u32 ep_addr;
        /* bus address of source or destination memory in the Root Complex */
        u32 rc_addr_h;
        u32 rc_addr_l;
} __attribute__ ((packed));

/**
 * Descriptor Table, an array of descriptors describing a chained transfer.
 *
 * An array of descriptors, preceded by workspace for the End Point.
 * It exists in Root Complex memory.
 *
 * The End Point can update its last completed descriptor number in the
 * eplast field if requested by setting the EPLAST_ENA bit either
 * globally in the header's or locally in any descriptor's control field.
 *
 * @note this structure may not exceed 4096 bytes. This results in a
 * maximum of 4096 / (4 * 4) - 1 = 255 descriptors per chained transfer.
 *
 * @see ug_pci_express 8.0, tables 7-9, 7-10 and 7-11 at page 7-17 and page 7-18.
 */
struct ape_chdma_table {
        /* workspace 0x00-0x0b, reserved */
        u32 reserved1[3];
        /* workspace 0x0c-0x0f, last descriptor handled by End Point */
        u32 w3;
        /* the actual array of descriptors
    * 0x10-0x1f, 0x20-0x2f, ... 0xff0-0xfff (255 entries)
    */
        struct ape_chdma_desc desc[255];
} __attribute__ ((packed));

/**
 * Altera PCI Express ('ape') board specific book keeping data
 *
 * Keeps state of the PCIe core and the Chaining DMA controller
 * application.
 */
struct ape_dev {
        /** the kernel pci device data structure provided by probe() */
        struct pci_dev *pci_dev;
        /**
         * kernel virtual address of the mapped BAR memory and IO regions of
         * the End Point. Used by map_bars()/unmap_bars().
         */
        void * __iomem bar[APE_BAR_NUM];
        /** kernel virtual address for Descriptor Table in Root Complex memory */
        struct ape_chdma_table *table_virt;
        /**
         * bus address for the Descriptor Table in Root Complex memory, in
         * CPU-native endianess
         */
        dma_addr_t table_bus;
        /* if the device regions could not be allocated, assume and remember it
         * is in use by another driver; this driver must not disable the device.
         */
        int in_use;
        /* whether this driver enabled msi for the device */
        int msi_enabled;
        /* whether this driver could obtain the regions */
        int got_regions;
        /* irq line succesfully requested by this driver, -1 otherwise */
        int irq_line;
        /* board revision */
        u8 revision;
        /* interrupt count, incremented by the interrupt handler */
        int irq_count;
#if ALTPCIECHDMA_CDEV
        /* character device */
        dev_t cdevno;
        struct cdev cdev;
        /* user space scatter gather mapper */
        struct sg_mapping_t *sgm;
#endif
};

/**
 * Using the subsystem vendor id and subsystem id, it is possible to
 * distinguish between different cards bases around the same
 * (third-party) logic core.
 *
 * Default Altera vendor and device ID's, and some (non-reserved)
 * ID's are now used here that are used amongst the testers/developers.
 */
static const struct pci_device_id ids[] = {
        { PCI_DEVICE(0x1172, 0xE001), },
        { PCI_DEVICE(0x2071, 0x2071), },
        { 0, }
};
MODULE_DEVICE_TABLE(pci, ids);

#if ALTPCIECHDMA_CDEV
/* prototypes for character device */
static int sg_init(struct ape_dev *ape);
static void sg_exit(struct ape_dev *ape);
#endif

/**
 * altpciechdma_isr() - Interrupt handler
 *
 */
static irqreturn_t altpciechdma_isr(int irq, void *dev_id)
{
        struct ape_dev *ape = (struct ape_dev *)dev_id;
        if (!ape)
                return IRQ_NONE;
        ape->irq_count++;
        return IRQ_HANDLED;
}

static int __devinit scan_bars(struct ape_dev *ape, struct pci_dev *dev)
{
        int i;
        for (i = 0; i < APE_BAR_NUM; i++) {
                unsigned long bar_start = pci_resource_start(dev, i);
                if (bar_start) {
                        unsigned long bar_end = pci_resource_end(dev, i);
                        unsigned long bar_flags = pci_resource_flags(dev, i);
                        printk(KERN_DEBUG "BAR%d 0x%08lx-0x%08lx flags 0x%08lx\n",
                          i, bar_start, bar_end, bar_flags);
                }
        }
        return 0;
}

/**
 * Unmap the BAR regions that had been mapped earlier using map_bars()
 */
static void unmap_bars(struct ape_dev *ape, struct pci_dev *dev)
{
        int i;
        for (i = 0; i < APE_BAR_NUM; i++) {
          /* is this BAR mapped? */
                if (ape->bar[i]) {
                        /* unmap BAR */
                        pci_iounmap(dev, ape->bar[i]);
                        ape->bar[i] = NULL;
                }
        }
}

/**
 * Map the device memory regions into kernel virtual address space after
 * verifying their sizes respect the minimum sizes needed, given by the
 * bar_min_len[] array.
 */
static int __devinit map_bars(struct ape_dev *ape, struct pci_dev *dev)
{
        int rc;
        int i;
        /* iterate through all the BARs */
        for (i = 0; i < APE_BAR_NUM; i++) {
                unsigned long bar_start = pci_resource_start(dev, i);
                unsigned long bar_end = pci_resource_end(dev, i);
                unsigned long bar_length = bar_end - bar_start + 1;
                ape->bar[i] = NULL;
                /* do not map, and skip, BARs with length 0 */
                if (!bar_min_len[i])
                        continue;
                /* do not map BARs with address 0 */
                if (!bar_start || !bar_end) {
                        printk(KERN_DEBUG "BAR #%d is not present?!\n", i);
                        rc = -1;
                        goto fail;
                }
                bar_length = bar_end - bar_start + 1;
                /* BAR length is less than driver requires? */
                if (bar_length < bar_min_len[i]) {
                        printk(KERN_DEBUG "BAR #%d length = %lu bytes but driver "
                        "requires at least %lu bytes\n",
                        i, bar_length, bar_min_len[i]);
                        rc = -1;
                        goto fail;
                }
                /* map the device memory or IO region into kernel virtual
                 * address space */
                ape->bar[i] = pci_iomap(dev, i, bar_min_len[i]);
                if (!ape->bar[i]) {
                        printk(KERN_DEBUG "Could not map BAR #%d.\n", i);
                        rc = -1;
                        goto fail;
                }
                printk(KERN_DEBUG "BAR[%d] mapped at 0x%p with length %lu(/%lu).\n", i,
                ape->bar[i], bar_min_len[i], bar_length);
        }
        /* succesfully mapped all required BAR regions */
        rc = 0;
        goto success;
fail:
        /* unmap any BARs that we did map */
        unmap_bars(ape, dev);
success:
        return rc;
}

#if 0 /* not yet implemented fully FIXME add opcode */
static void __devinit rcslave_test(struct ape_dev *ape, struct pci_dev *dev)
{
        u32 *rcslave_mem = (u32 *)ape->bar[APE_BAR_RCSLAVE];
        u32 result = 0;
        /** this number is assumed to be different each time this test runs */
        u32 seed = (u32)jiffies;
        u32 value = seed;
        int i;

        /* write loop */
        value = seed;
        for (i = 1024; i < 32768 / 4 ; i++) {
                printk(KERN_DEBUG "Writing 0x%08x to 0x%p.\n",
                        (u32)value, (void *)rcslave_mem + i);
                iowrite32(value, rcslave_mem + i);
                value++;
        }
        /* read-back loop */
        value = seed;
        for (i = 1024; i < 32768 / 4; i++) {
                result = ioread32(rcslave_mem + i);
                if (result != value) {
                        printk(KERN_DEBUG "Wrote 0x%08x to 0x%p, but read back 0x%08x.\n",
                                (u32)value, (void *)rcslave_mem + i, (u32)result);
                        break;
                }
                value++;
        }
}
#endif

/* obtain the 32 most significant (high) bits of a 32-bit or 64-bit address */
#define pci_dma_h(addr) ((addr >> 16) >> 16)
/* obtain the 32 least significant (low) bits of a 32-bit or 64-bit address */
#define pci_dma_l(addr) (addr & 0xffffffffUL)

/* ape_fill_chdma_desc() - Fill a Altera PCI Express Chaining DMA descriptor
 *
 * @desc pointer to descriptor to be filled
 * @addr root complex address
 * @ep_addr end point address
 * @len number of bytes, must be a multiple of 4.
 */
static inline void ape_chdma_desc_set(struct ape_chdma_desc *desc, dma_addr_t addr, u32 ep_addr, int len)
{
  BUG_ON(len & 3);
        desc->w0 = cpu_to_le32(len / 4);
        desc->ep_addr = cpu_to_le32(ep_addr);
        desc->rc_addr_h = cpu_to_le32(pci_dma_h(addr));
        desc->rc_addr_l = cpu_to_le32(pci_dma_l(addr));
}

#if ALTPCIECHDMA_CDEV
/*
 * ape_sg_to_chdma_table() - Create a device descriptor table from a scatterlist.
 *
 * The scatterlist must have been mapped by pci_map_sg(sgm->sgl).
 *
 * @sgl scatterlist.
 * @nents Number of entries in the scatterlist.
 * @first Start index in the scatterlist sgm->sgl.
 * @ep_addr End Point address for the scatter/gather transfer.
 * @desc pointer to first descriptor
 *
 * Returns Number of entries in the table on success, -1 on error.
 */
static int ape_sg_to_chdma_table(struct scatterlist *sgl, int nents, int first, struct ape_chdma_desc *desc, u32 ep_addr)
{
        int i = first, j = 0;
        /* inspect first entry */
        dma_addr_t addr = sg_dma_address(&sgl[i]);
        unsigned int len = sg_dma_len(&sgl[i]);
        /* contiguous block */
        dma_addr_t cont_addr = addr;
        unsigned int cont_len = len;
        /* iterate over remaining entries */
        for (; j < 25 && i < nents - 1; i++) {
                /* bus address of next entry i + 1 */
                dma_addr_t next = sg_dma_address(&sgl[i + 1]);
                /* length of this entry i */
                len = sg_dma_len(&sgl[i]);
                printk(KERN_DEBUG "%04d: addr=0x%Lx length=0x%08x\n", i,
                        (unsigned long long)addr, len);
                /* entry i + 1 is non-contiguous with entry i? */
                if (next != addr + len) {
                        /* TODO create entry here (we could overwrite i) */
                        printk(KERN_DEBUG "%4d: cont_addr=0x%Lx cont_len=0x%08x\n", j,
                                (unsigned long long)cont_addr, cont_len);
                        /* set descriptor for contiguous transfer */
                        ape_chdma_desc_set(&desc[j], cont_addr, ep_addr, cont_len);
                        /* next end point memory address */
                        ep_addr += cont_len;
                        /* start new contiguous block */
                        cont_addr = next;
                        cont_len = 0;
                        j++;
                }
                /* add entry i + 1 to current contiguous block */
                cont_len += len;
                /* goto entry i + 1 */
                addr = next;
        }
        /* TODO create entry here  (we could overwrite i) */
        printk(KERN_DEBUG "%04d: addr=0x%Lx length=0x%08x\n", i,
                (unsigned long long)addr, len);
        printk(KERN_DEBUG "%4d: cont_addr=0x%Lx length=0x%08x\n", j,
                (unsigned long long)cont_addr, cont_len);
        j++;
        return j;
}
#endif

/* compare buffers */
static inline int compare(u32 *p, u32 *q, int len)
{
        int result = -1;
        int fail = 0;
        int i;
        for (i = 0; i < len / 4; i++) {
                if (*p == *q) {
                        /* every so many u32 words, show equals */
                        if ((i & 255) == 0)
                                printk(KERN_DEBUG "[%p] = 0x%08x    [%p] = 0x%08x\n", p, *p, q, *q);
                } else {
                        fail++;
                        /* show the first few miscompares */
                        if (fail < 10)
                                printk(KERN_DEBUG "[%p] = 0x%08x != [%p] = 0x%08x ?!\n", p, *p, q, *q);
                                /* but stop after a while */
                        else if (fail == 10)
                                printk(KERN_DEBUG "---more errors follow! not printed---\n");
                        else
                                /* stop compare after this many errors */
                        break;
                }
                p++;
                q++;
        }
        if (!fail)
                result = 0;
        return result;
}

/* dma_test() - Perform DMA loop back test to end point and back to root complex.
 *
 * Allocate a cache-coherent buffer in host memory, consisting of four pages.
 *
 * Fill the four memory pages such that each 32-bit word contains its own address.
 *
 * Now perform a loop back test, have the end point device copy the first buffer
 * half to end point memory, then have it copy back into the second half.
 *
 *   Create a descriptor table to copy the first buffer half into End Point
 *   memory. Instruct the End Point to do a DMA read using that table.
 *
 *   Create a descriptor table to copy End Point memory to the second buffer
 *   half. Instruct the End Point to do a DMA write using that table.
 *
 * Compare results, fail or pass.
 *
 */
static int __devinit dma_test(struct ape_dev *ape, struct pci_dev *dev)
{
        /* test result; guilty until proven innocent */
        int result = -1;
        /* the DMA read header sits at address 0x00 of the DMA engine BAR */
        struct ape_chdma_header *write_header = (struct ape_chdma_header *)ape->bar[APE_BAR_HEADER];
        /* the write DMA header sits after the read header at address 0x10 */
        struct ape_chdma_header *read_header = write_header + 1;
        /* virtual address of the allocated buffer */
        u8 *buffer_virt = 0;
        /* bus address of the allocated buffer */
        dma_addr_t buffer_bus = 0;
        int i, n = 0, irq_count;

        /* temporary value used to construct 32-bit data words */
        u32 w;

        printk(KERN_DEBUG "bar_tests(), PAGE_SIZE = 0x%0x\n", (int)PAGE_SIZE);
        printk(KERN_DEBUG "write_header = 0x%p.\n", write_header);
        printk(KERN_DEBUG "read_header = 0x%p.\n", read_header);
        printk(KERN_DEBUG "&write_header->w3 = 0x%p\n", &write_header->w3);
        printk(KERN_DEBUG "&read_header->w3 = 0x%p\n", &read_header->w3);
        printk(KERN_DEBUG "ape->table_virt = 0x%p.\n", ape->table_virt);

        if (!write_header || !read_header || !ape->table_virt)
                goto fail;

        /* allocate and map coherently-cached memory for a DMA-able buffer */
        /* @see Documentation/PCI/PCI-DMA-mapping.txt, near line 318 */
        buffer_virt = (u8 *)pci_alloc_consistent(dev, PAGE_SIZE * 4, &buffer_bus);
        if (!buffer_virt) {
                printk(KERN_DEBUG "Could not allocate coherent DMA buffer.\n");
                goto fail;
        }
        printk(KERN_DEBUG "Allocated cache-coherent DMA buffer (virtual address = %p, bus address = 0x%016llx).\n",
               buffer_virt, (u64)buffer_bus);

        /* fill first half of buffer with its virtual address as data */
        for (i = 0; i < 4 * PAGE_SIZE; i += 4)
#if 0
                *(u32 *)(buffer_virt + i) = i / PAGE_SIZE + 1;
#else
                *(u32 *)(buffer_virt + i) = (u32)(unsigned long)(buffer_virt + i);
#endif
#if 0
  compare((u32 *)buffer_virt, (u32 *)(buffer_virt + 2 * PAGE_SIZE), 8192);
#endif

#if 0
        /* fill second half of buffer with zeroes */
        for (i = 2 * PAGE_SIZE; i < 4 * PAGE_SIZE; i += 4)
                *(u32 *)(buffer_virt + i) = 0;
#endif

        /* invalidate EPLAST, outside 0-255, 0xFADE is from the testbench */
        ape->table_virt->w3 = cpu_to_le32(0x0000FADE);

        /* fill in first descriptor */
        n = 0;
        /* read 8192 bytes from RC buffer to EP address 4096 */
        ape_chdma_desc_set(&ape->table_virt->desc[n], buffer_bus, 4096, 2 * PAGE_SIZE);
#if 1
        for (i = 0; i < 255; i++)
                ape_chdma_desc_set(&ape->table_virt->desc[i], buffer_bus, 4096, 2 * PAGE_SIZE);
        /* index of last descriptor */
        n = i - 1;
#endif
#if 0
        /* fill in next descriptor */
        n++;
        /* read 1024 bytes from RC buffer to EP address 4096 + 1024 */
        ape_chdma_desc_set(&ape->table_virt->desc[n], buffer_bus + 1024, 4096 + 1024, 1024);
#endif

#if 1
        /* enable MSI after the last descriptor is completed */
        if (ape->msi_enabled)
                ape->table_virt->desc[n].w0 |= cpu_to_le32(1UL << 16)/*local MSI*/;
#endif
#if 0
        /* dump descriptor table for debugging */
        printk(KERN_DEBUG "Descriptor Table (Read, in Root Complex Memory, # = %d)\n", n + 1);
        for (i = 0; i < 4 + (n + 1) * 4; i += 4) {
                u32 *p = (u32 *)ape->table_virt;
                p += i;
                printk(KERN_DEBUG "0x%08x/0x%02x: 0x%08x (LEN=0x%x)\n", (u32)p, (u32)p & 15, *p, 4 * le32_to_cpu(*p));
                p++;
                printk(KERN_DEBUG "0x%08x/0x%02x: 0x%08x (EPA=0x%x)\n", (u32)p, (u32)p & 15, *p, le32_to_cpu(*p));
                p++;
                printk(KERN_DEBUG "0x%08x/0x%02x: 0x%08x (RCH=0x%x)\n", (u32)p, (u32)p & 15, *p, le32_to_cpu(*p));
                p++;
                printk(KERN_DEBUG "0x%08x/0x%02x: 0x%08x (RCL=0x%x)\n", (u32)p, (u32)p & 15, *p, le32_to_cpu(*p));
        }
#endif
        /* set available number of descriptors in table */
        w = (u32)(n + 1);
        w |= (1UL << 18)/*global EPLAST_EN*/;
#if 0
        if (ape->msi_enabled)
                w |= (1UL << 17)/*global MSI*/;
#endif
        printk(KERN_DEBUG "writing 0x%08x to 0x%p\n", w, (void *)&read_header->w0);
        iowrite32(w, &read_header->w0);

        /* write table address (higher 32-bits) */
        printk(KERN_DEBUG "writing 0x%08x to 0x%p\n", (u32)((ape->table_bus >> 16) >> 16), (void *)&read_header->bdt_addr_h);
        iowrite32(pci_dma_h(ape->table_bus), &read_header->bdt_addr_h);

        /* write table address (lower 32-bits) */
        printk(KERN_DEBUG "writing 0x%08x to 0x%p\n", (u32)(ape->table_bus & 0xffffffffUL), (void *)&read_header->bdt_addr_l);
        iowrite32(pci_dma_l(ape->table_bus), &read_header->bdt_addr_l);

        /* memory write barrier */
        wmb();
        printk(KERN_DEBUG "Flush posted writes\n");
        /** FIXME Add dummy read to flush posted writes but need a readable location! */
#if 0
        (void)ioread32();
#endif

        /* remember IRQ count before the transfer */
        irq_count = ape->irq_count;
        /* write number of descriptors - this starts the DMA */
        printk(KERN_DEBUG "\nStart DMA read\n");
        printk(KERN_DEBUG "writing 0x%08x to 0x%p\n", (u32)n, (void *)&read_header->w3);
        iowrite32(n, &read_header->w3);
        printk(KERN_DEBUG "EPLAST = %lu\n", le32_to_cpu(*(u32 *)&ape->table_virt->w3) & 0xffffUL);

        /** memory write barrier */
        wmb();
        /* dummy read to flush posted writes */
        /* FIXME Need a readable location! */
#if 0
        (void)ioread32();
#endif
        printk(KERN_DEBUG "POLL FOR READ:\n");
        /* poll for chain completion, 1000 times 1 millisecond */
        for (i = 0; i < 100; i++) {
                volatile u32 *p = &ape->table_virt->w3;
                u32 eplast = le32_to_cpu(*p) & 0xffffUL;
                printk(KERN_DEBUG "EPLAST = %u, n = %d\n", eplast, n);
                if (eplast == n) {
                        printk(KERN_DEBUG "DONE\n");
                        /* print IRQ count before the transfer */
                        printk(KERN_DEBUG "#IRQs during transfer: %d\n", ape->irq_count - irq_count);
                        break;
                }
                udelay(100);
        }

        /* invalidate EPLAST, outside 0-255, 0xFADE is from the testbench */
        ape->table_virt->w3 = cpu_to_le32(0x0000FADE);

        /* setup first descriptor */
        n = 0;
        ape_chdma_desc_set(&ape->table_virt->desc[n], buffer_bus + 8192, 4096, 2 * PAGE_SIZE);
#if 1
        for (i = 0; i < 255; i++)
                ape_chdma_desc_set(&ape->table_virt->desc[i], buffer_bus + 8192, 4096, 2 * PAGE_SIZE);

        /* index of last descriptor */
        n = i - 1;
#endif
#if 1 /* test variable, make a module option later */
        if (ape->msi_enabled)
                ape->table_virt->desc[n].w0 |= cpu_to_le32(1UL << 16)/*local MSI*/;
#endif
#if 0
        /* dump descriptor table for debugging */
        printk(KERN_DEBUG "Descriptor Table (Write, in Root Complex Memory, # = %d)\n", n + 1);
        for (i = 0; i < 4 + (n + 1) * 4; i += 4) {
                u32 *p = (u32 *)ape->table_virt;
                p += i;
                printk(KERN_DEBUG "0x%08x/0x%02x: 0x%08x (LEN=0x%x)\n", (u32)p, (u32)p & 15, *p, 4 * le32_to_cpu(*p));
                p++;
                printk(KERN_DEBUG "0x%08x/0x%02x: 0x%08x (EPA=0x%x)\n", (u32)p, (u32)p & 15, *p, le32_to_cpu(*p));
                p++;
                printk(KERN_DEBUG "0x%08x/0x%02x: 0x%08x (RCH=0x%x)\n", (u32)p, (u32)p & 15, *p, le32_to_cpu(*p));
                p++;
                printk(KERN_DEBUG "0x%08x/0x%02x: 0x%08x (RCL=0x%x)\n", (u32)p, (u32)p & 15, *p, le32_to_cpu(*p));
        }
#endif

        /* set number of available descriptors in the table */
        w = (u32)(n + 1);
        /* enable updates of eplast for each descriptor completion */
        w |= (u32)(1UL << 18)/*global EPLAST_EN*/;
#if 0   /* test variable, make a module option later */
        /* enable MSI for each descriptor completion */
        if (ape->msi_enabled)
                w |= (1UL << 17)/*global MSI*/;
#endif
        iowrite32(w, &write_header->w0);
        iowrite32(pci_dma_h(ape->table_bus), &write_header->bdt_addr_h);
        iowrite32(pci_dma_l(ape->table_bus), &write_header->bdt_addr_l);

        /** memory write barrier and flush posted writes */
        wmb();
        /* dummy read to flush posted writes */
        /* FIXME Need a readable location! */
#if 0
        (void)ioread32();
#endif
        irq_count = ape->irq_count;

        printk(KERN_DEBUG "\nStart DMA write\n");
        iowrite32(n, &write_header->w3);

        /** memory write barrier */
        wmb();
        /** dummy read to flush posted writes */
        /* (void) ioread32(); */

        printk(KERN_DEBUG "POLL FOR WRITE:\n");
        /* poll for completion, 1000 times 1 millisecond */
        for (i = 0; i < 100; i++) {
                volatile u32 *p = &ape->table_virt->w3;
                u32 eplast = le32_to_cpu(*p) & 0xffffUL;
                printk(KERN_DEBUG "EPLAST = %u, n = %d\n", eplast, n);
                if (eplast == n) {
                        printk(KERN_DEBUG "DONE\n");
                        /* print IRQ count before the transfer */
                        printk(KERN_DEBUG "#IRQs during transfer: %d\n", ape->irq_count - irq_count);
                        break;
                }
                udelay(100);
        }
        /* soft-reset DMA write engine */
        iowrite32(0x0000ffffUL, &write_header->w0);
        /* soft-reset DMA read engine */
        iowrite32(0x0000ffffUL, &read_header->w0);

        /** memory write barrier */
        wmb();
        /* dummy read to flush posted writes */
        /* FIXME Need a readable location! */
#if 0
        (void)ioread32();
#endif
        /* compare first half of buffer with second half, should be identical */
        result = compare((u32 *)buffer_virt, (u32 *)(buffer_virt + 2 * PAGE_SIZE), 8192);
        printk(KERN_DEBUG "DMA loop back test %s.\n", result ? "FAILED" : "PASSED");

        pci_free_consistent(dev, 4 * PAGE_SIZE, buffer_virt, buffer_bus);
fail:
        printk(KERN_DEBUG "bar_tests() end, result %d\n", result);
        return result;
}

/* Called when the PCI sub system thinks we can control the given device.
 * Inspect if we can support the device and if so take control of it.
 *
 * Return 0 when we have taken control of the given device.
 *
 * - allocate board specific bookkeeping
 * - allocate coherently-mapped memory for the descriptor table
 * - enable the board
 * - verify board revision
 * - request regions
 * - query DMA mask
 * - obtain and request irq
 * - map regions into kernel address space
 */
static int __devinit probe(struct pci_dev *dev, const struct pci_device_id *id)
{
        int rc = 0;
        struct ape_dev *ape = NULL;
        u8 irq_pin, irq_line;
        printk(KERN_DEBUG "probe(dev = 0x%p, pciid = 0x%p)\n", dev, id);

        /* allocate memory for per-board book keeping */
        ape = kzalloc(sizeof(struct ape_dev), GFP_KERNEL);
        if (!ape) {
                printk(KERN_DEBUG "Could not kzalloc()ate memory.\n");
                goto err_ape;
        }
        ape->pci_dev = dev;
        dev_set_drvdata(&dev->dev, ape);
        printk(KERN_DEBUG "probe() ape = 0x%p\n", ape);

        printk(KERN_DEBUG "sizeof(struct ape_chdma_table) = %d.\n",
                (int)sizeof(struct ape_chdma_table));
        /* the reference design has a size restriction on the table size */
        BUG_ON(sizeof(struct ape_chdma_table) > APE_CHDMA_TABLE_SIZE);

        /* allocate and map coherently-cached memory for a descriptor table */
        /* @see LDD3 page 446 */
        ape->table_virt = (struct ape_chdma_table *)pci_alloc_consistent(dev,
                APE_CHDMA_TABLE_SIZE, &ape->table_bus);
        /* could not allocate table? */
        if (!ape->table_virt) {
                printk(KERN_DEBUG "Could not dma_alloc()ate_coherent memory.\n");
                goto err_table;
        }

        printk(KERN_DEBUG "table_virt = %p, table_bus = 0x%16llx.\n",
                ape->table_virt, (u64)ape->table_bus);

        /* enable device */
        rc = pci_enable_device(dev);
        if (rc) {
                printk(KERN_DEBUG "pci_enable_device() failed\n");
                goto err_enable;
        }

        /* enable bus master capability on device */
        pci_set_master(dev);
        /* enable message signaled interrupts */
        rc = pci_enable_msi(dev);
        /* could not use MSI? */
        if (rc) {
                /* resort to legacy interrupts */
                printk(KERN_DEBUG "Could not enable MSI interrupting.\n");
                ape->msi_enabled = 0;
        /* MSI enabled, remember for cleanup */
        } else {
                printk(KERN_DEBUG "Enabled MSI interrupting.\n");
                ape->msi_enabled = 1;
        }

        pci_read_config_byte(dev, PCI_REVISION_ID, &ape->revision);
#if 0 /* example */
        /* (for example) this driver does not support revision 0x42 */
    if (ape->revision == 0x42) {
                printk(KERN_DEBUG "Revision 0x42 is not supported by this driver.\n");
                rc = -ENODEV;
                goto err_rev;
        }
#endif
        /** XXX check for native or legacy PCIe endpoint? */

        rc = pci_request_regions(dev, DRV_NAME);
        /* could not request all regions? */
        if (rc) {
                /* assume device is in use (and do not disable it later!) */
                ape->in_use = 1;
                goto err_regions;
        }
        ape->got_regions = 1;

#if 1   /* @todo For now, disable 64-bit, because I do not understand the implications (DAC!) */
        /* query for DMA transfer */
        /* @see Documentation/PCI/PCI-DMA-mapping.txt */
        if (!pci_set_dma_mask(dev, DMA_BIT_MASK(64))) {
                pci_set_consistent_dma_mask(dev, DMA_BIT_MASK(64));
                /* use 64-bit DMA */
                printk(KERN_DEBUG "Using a 64-bit DMA mask.\n");
        } else
#endif
        if (!pci_set_dma_mask(dev, DMA_BIT_MASK(32))) {
                printk(KERN_DEBUG "Could not set 64-bit DMA mask.\n");
                pci_set_consistent_dma_mask(dev, DMA_BIT_MASK(32));
                /* use 32-bit DMA */
                printk(KERN_DEBUG "Using a 32-bit DMA mask.\n");
        } else {
                printk(KERN_DEBUG "No suitable DMA possible.\n");
                /** @todo Choose proper error return code */
                rc = -1;
                goto err_mask;
        }

        rc = pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &irq_pin);
        /* could not read? */
        if (rc)
                goto err_irq;
        printk(KERN_DEBUG "IRQ pin #%d (0=none, 1=INTA#...4=INTD#).\n", irq_pin);

        /* @see LDD3, page 318 */
        rc = pci_read_config_byte(dev, PCI_INTERRUPT_LINE, &irq_line);
        /* could not read? */
        if (rc) {
                printk(KERN_DEBUG "Could not query PCI_INTERRUPT_LINE, error %d\n", rc);
                goto err_irq;
        }
        printk(KERN_DEBUG "IRQ line #%d.\n", irq_line);
#if 1
        irq_line = dev->irq;
        /* @see LDD3, page 259 */
        rc = request_irq(irq_line, altpciechdma_isr, IRQF_SHARED, DRV_NAME, (void *)ape);
        if (rc) {
                printk(KERN_DEBUG "Could not request IRQ #%d, error %d\n", irq_line, rc);
                ape->irq_line = -1;
                goto err_irq;
        }
        /* remember which irq we allocated */
        ape->irq_line = (int)irq_line;
        printk(KERN_DEBUG "Succesfully requested IRQ #%d with dev_id 0x%p\n", irq_line, ape);
#endif
        /* show BARs */
        scan_bars(ape, dev);
        /* map BARs */
        rc = map_bars(ape, dev);
        if (rc)
                goto err_map;
#if ALTPCIECHDMA_CDEV
        /* initialize character device */
        rc = sg_init(ape);
        if (rc)
                goto err_cdev;
#endif
        /* perform DMA engines loop back test */
        rc = dma_test(ape, dev);
        (void)rc;
        /* succesfully took the device */
        rc = 0;
        printk(KERN_DEBUG "probe() successful.\n");
        goto end;
#if ALTPCIECHDMA_CDEV
err_cdev:
        /* unmap the BARs */
        unmap_bars(ape, dev);
#endif
err_map:
        /* free allocated irq */
        if (ape->irq_line >= 0)
                free_irq(ape->irq_line, (void *)ape);
err_irq:
        if (ape->msi_enabled)
                pci_disable_msi(dev);
        /* disable the device iff it is not in use */
        if (!ape->in_use)
                pci_disable_device(dev);
        if (ape->got_regions)
                pci_release_regions(dev);
err_mask:
err_regions:
/*err_rev:*/
/* clean up everything before device enable() */
err_enable:
        if (ape->table_virt)
                pci_free_consistent(dev, APE_CHDMA_TABLE_SIZE, ape->table_virt, ape->table_bus);
/* clean up everything before allocating descriptor table */
err_table:
        if (ape)
                kfree(ape);
err_ape:
end:
        return rc;
}

static void __devexit remove(struct pci_dev *dev)
{
        struct ape_dev *ape = dev_get_drvdata(&dev->dev);

        printk(KERN_DEBUG "remove(0x%p)\n", dev);
        printk(KERN_DEBUG "remove(dev = 0x%p) where ape = 0x%p\n", dev, ape);

        /* remove character device */
#if ALTPCIECHDMA_CDEV
        sg_exit(ape);
#endif

        if (ape->table_virt)
                pci_free_consistent(dev, APE_CHDMA_TABLE_SIZE, ape->table_virt, ape->table_bus);

        /* free IRQ
         * @see LDD3 page 279
         */
        if (ape->irq_line >= 0) {
                printk(KERN_DEBUG "Freeing IRQ #%d for dev_id 0x%08lx.\n",
                ape->irq_line, (unsigned long)ape);
                free_irq(ape->irq_line, (void *)ape);
        }
        /* MSI was enabled? */
        if (ape->msi_enabled) {
                /* Disable MSI @see Documentation/MSI-HOWTO.txt */
                pci_disable_msi(dev);
                ape->msi_enabled = 0;
        }
        /* unmap the BARs */
        unmap_bars(ape, dev);
        if (!ape->in_use)
                pci_disable_device(dev);
        if (ape->got_regions)
                /* to be called after device disable */
                pci_release_regions(dev);
}

#if ALTPCIECHDMA_CDEV

/*
 * Called when the device goes from unused to used.
 */
static int sg_open(struct inode *inode, struct file *file)
{
        struct ape_dev *ape;
        printk(KERN_DEBUG DRV_NAME "_open()\n");
        /* pointer to containing data structure of the character device inode */
        ape = container_of(inode->i_cdev, struct ape_dev, cdev);
        /* create a reference to our device state in the opened file */
        file->private_data = ape;
        /* create virtual memory mapper */
        ape->sgm = sg_create_mapper(MAX_CHDMA_SIZE);
        return 0;
}

/*
 * Called when the device goes from used to unused.
 */
static int sg_close(struct inode *inode, struct file *file)
{
        /* fetch device specific data stored earlier during open */
        struct ape_dev *ape = (struct ape_dev *)file->private_data;
        printk(KERN_DEBUG DRV_NAME "_close()\n");
        /* destroy virtual memory mapper */
        sg_destroy_mapper(ape->sgm);
        return 0;
}

static ssize_t sg_read(struct file *file, char __user *buf, size_t count, loff_t *pos)
{
        /* fetch device specific data stored earlier during open */
        struct ape_dev *ape = (struct ape_dev *)file->private_data;
        (void)ape;
        printk(KERN_DEBUG DRV_NAME "_read(buf=0x%p, count=%lld, pos=%llu)\n", buf, (s64)count, (u64)*pos);
        return count;
}

/* sg_write() - Write to the device
 *
 * @buf userspace buffer
 * @count number of bytes in the userspace buffer
 *
 * Iterate over the userspace buffer, taking at most 255 * PAGE_SIZE bytes for
 * each DMA transfer.
 *   For each transfer, get the user pages, build a sglist, map, build a
 *   descriptor table. submit the transfer. wait for the interrupt handler
 *   to wake us on completion.
 */
static ssize_t sg_write(struct file *file, const char __user *buf, size_t count, loff_t *pos)
{
        int hwnents, tents;
        size_t transfer_len, remaining = count, done = 0;
        u64 transfer_addr = (u64)buf;
        /* fetch device specific data stored earlier during open */
        struct ape_dev *ape = (struct ape_dev *)file->private_data;
        printk(KERN_DEBUG DRV_NAME "_write(buf=0x%p, count=%lld, pos=%llu)\n",
                buf, (s64)count, (u64)*pos);
        /* TODO transfer boundaries at PAGE_SIZE granularity */
        while (remaining > 0) {
                /* limit DMA transfer size */
                transfer_len = (remaining < APE_CHDMA_MAX_TRANSFER_LEN) ? remaining :
                        APE_CHDMA_MAX_TRANSFER_LEN;
                /* get all user space buffer pages and create a scattergather list */
                sgm_map_user_pages(ape->sgm, transfer_addr, transfer_len, 0/*read from userspace*/);
                printk(KERN_DEBUG DRV_NAME "mapped_pages=%d\n", ape->sgm->mapped_pages);
                /* map all entries in the scattergather list */
                hwnents = pci_map_sg(ape->pci_dev, ape->sgm->sgl, ape->sgm->mapped_pages, DMA_TO_DEVICE);
                printk(KERN_DEBUG DRV_NAME "hwnents=%d\n", hwnents);
                /* build device descriptor tables and submit them to the DMA engine */
                tents = ape_sg_to_chdma_table(ape->sgm->sgl, hwnents, 0, &ape->table_virt->desc[0], 4096);
                printk(KERN_DEBUG DRV_NAME "tents=%d\n", hwnents);
#if 0
                while (tables) {
                        /* TODO build table */
                        /* TODO submit table to the device */
                        /* if engine stopped and unfinished work then start engine */
                }
                put ourselves on wait queue
#endif

                dma_unmap_sg(NULL, ape->sgm->sgl, ape->sgm->mapped_pages, DMA_TO_DEVICE);
                /* dirty and free the pages */
                sgm_unmap_user_pages(ape->sgm, 1/*dirtied*/);
                /* book keeping */
                transfer_addr += transfer_len;
                remaining -= transfer_len;
                done += transfer_len;
        }
        return done;
}

/*
 * character device file operations
 */
static const struct file_operations sg_fops = {
        .owner = THIS_MODULE,
        .open = sg_open,
        .release = sg_close,
        .read = sg_read,
        .write = sg_write,
};

/* sg_init() - Initialize character device
 *
 * XXX Should ideally be tied to the device, on device probe, not module init.
 */
static int sg_init(struct ape_dev *ape)
{
        int rc;
        printk(KERN_DEBUG DRV_NAME " sg_init()\n");
        /* allocate a dynamically allocated character device node */
        rc = alloc_chrdev_region(&ape->cdevno, 0/*requested minor*/, 1/*count*/, DRV_NAME);
        /* allocation failed? */
        if (rc < 0) {
                printk("alloc_chrdev_region() = %d\n", rc);
                goto fail_alloc;
        }
        /* couple the device file operations to the character device */
        cdev_init(&ape->cdev, &sg_fops);
        ape->cdev.owner = THIS_MODULE;
        /* bring character device live */
        rc = cdev_add(&ape->cdev, ape->cdevno, 1/*count*/);
        if (rc < 0) {
                printk("cdev_add() = %d\n", rc);
                goto fail_add;
        }
        printk(KERN_DEBUG "altpciechdma = %d:%d\n", MAJOR(ape->cdevno), MINOR(ape->cdevno));
        return 0;
fail_add:
        /* free the dynamically allocated character device node */
    unregister_chrdev_region(ape->cdevno, 1/*count*/);
fail_alloc:
        return -1;
}

/* sg_exit() - Cleanup character device
 *
 * XXX Should ideally be tied to the device, on device remove, not module exit.
 */

static void sg_exit(struct ape_dev *ape)
{
        printk(KERN_DEBUG DRV_NAME " sg_exit()\n");
        /* remove the character device */
        cdev_del(&ape->cdev);
        /* free the dynamically allocated character device node */
        unregister_chrdev_region(ape->cdevno, 1/*count*/);
}

#endif /* ALTPCIECHDMA_CDEV */

/* used to register the driver with the PCI kernel sub system
 * @see LDD3 page 311
 */
static struct pci_driver pci_driver = {
        .name = DRV_NAME,
        .id_table = ids,
        .probe = probe,
        .remove = __devexit_p(remove),
        /* resume, suspend are optional */
};

/**
 * alterapciechdma_init() - Module initialization, registers devices.
 */
static int __init alterapciechdma_init(void)
{
        int rc = 0;
        printk(KERN_DEBUG DRV_NAME " init(), built at " __DATE__ " " __TIME__ "\n");
        /* register this driver with the PCI bus driver */
        rc = pci_register_driver(&pci_driver);
        if (rc < 0)
                return rc;
        return 0;
}

/**
 * alterapciechdma_init() - Module cleanup, unregisters devices.
 */
static void __exit alterapciechdma_exit(void)
{
        printk(KERN_DEBUG DRV_NAME " exit(), built at " __DATE__ " " __TIME__ "\n");
        /* unregister this driver from the PCI bus driver */
        pci_unregister_driver(&pci_driver);
}

MODULE_LICENSE("GPL");

module_init(alterapciechdma_init);
module_exit(alterapciechdma_exit);