Staging: add Driver for Altera PCI Express Chaining DMA reference design

Altera PCI Express Chaining DMA driver

A reference driver that exercises the Chaining DMA logic reference
design generated along the Altera FPGA PCI Express soft or hard core,
only if instantiated using the MegaWizard, not the SOPC builder, of
Quartus 8.1.

This driver can be used to test the logic instantiation and PCI
Express layers and acts as a starting point for driving custom logic
connected to the PCI Express End Point Chaining DMA engines.

Signed-off-by: Leon Woestenberg <leon@sidebranch.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

6 files changed, 1214 insertions, 0 deletions

diff --git a/drivers/staging/Kconfig b/drivers/staging/Kconfig
index 11d003d..48e2e06 100644
--- a/drivers/staging/Kconfig
+++ b/drivers/staging/Kconfig
@@ -79,5 +79,7 @@ source "drivers/staging/asus_oled/Kconfig"
 
 source "drivers/staging/panel/Kconfig"
 
+source "drivers/staging/altpciechdma/Kconfig"
+
 endif # !STAGING_EXCLUDE_BUILD
 endif # STAGING
diff --git a/drivers/staging/Makefile b/drivers/staging/Makefile
index a738bb3..b301be8 100644
--- a/drivers/staging/Makefile
+++ b/drivers/staging/Makefile
@@ -22,3 +22,4 @@ obj-$(CONFIG_BENET)		+= benet/
 obj-$(CONFIG_COMEDI)		+= comedi/
 obj-$(CONFIG_ASUS_OLED)		+= asus_oled/
 obj-$(CONFIG_PANEL)		+= panel/
+obj-$(CONFIG_ALTERA_PCIE_CHDMA)	+= altpciechdma/
diff --git a/drivers/staging/altpciechdma/Kconfig b/drivers/staging/altpciechdma/Kconfig
new file mode 100644
index 0000000..0f4bf92
--- /dev/null
+++ b/drivers/staging/altpciechdma/Kconfig
@@ -0,0 +1,10 @@
+config ALTERA_PCIE_CHDMA
+	tristate "Altera PCI Express Chaining DMA driver"
+	depends on PCI
+	default N
+	---help---
+	  A reference driver that exercises the Chaining DMA logic reference
+	  design generated along the Altera FPGA PCI Express soft or hard core,
+	  only if instantiated using the MegaWizard, not the SOPC builder, of
+	  Quartus 8.1.
+
diff --git a/drivers/staging/altpciechdma/Makefile b/drivers/staging/altpciechdma/Makefile
new file mode 100644
index 0000000..c08c843
--- /dev/null
+++ b/drivers/staging/altpciechdma/Makefile
@@ -0,0 +1,2 @@
+obj-$(CONFIG_ALTERA_PCIE_CHDMA)	+= altpciechdma.o
+
diff --git a/drivers/staging/altpciechdma/TODO b/drivers/staging/altpciechdma/TODO
new file mode 100644
index 0000000..12c945f
--- /dev/null
+++ b/drivers/staging/altpciechdma/TODO
@@ -0,0 +1,15 @@
+DONE:
+    - functionality similar to logic testbench
+
+TODO:
+	- checkpatch.pl cleanups.
+	- keep state of DMA engines.
+	- keep data structure that keeps state of each transfer.
+	- interrupt handler should iterate over outstanding descriptor tables.
+	- complete userspace cdev to read/write using the DMA engines.
+	- split off the DMA support functions in a module, re-usable by custom
+	  drivers.
+
+Please coordinate work with, and send patches to
+Leon Woestenberg <leon@sidebranch.com>
+
diff --git a/drivers/staging/altpciechdma/altpciechdma.c b/drivers/staging/altpciechdma/altpciechdma.c
new file mode 100644
index 0000000..8e2b4ca
--- /dev/null
+++ b/drivers/staging/altpciechdma/altpciechdma.c
@@ -0,0 +1,1184 @@
+/**
+ * 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/delay.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));
+}
+
+/*
+ * 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%08x length=0x%08x\n", i, 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%08x cont_len=0x%08x\n", j, 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%08x length=0x%08x\n", i, addr, len);
+	printk(KERN_DEBUG "%4d: cont_addr=0x%08x length=0x%08x\n", j, cont_addr, cont_len);
+	j++;
+	return j;
+}
+
+/* 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 2.6.26.2/Documentation/DMA-mapping.txt 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 = 0x%016llx, bus address = 0x%016llx).\n",
+		(u64)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) = (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->dev.driver_data = (void *)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 = 0x%16llx, table_bus = 0x%16llx.\n",
+		(u64)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/DMA-mapping.txt */
+	if (!pci_set_dma_mask(dev, DMA_64BIT_MASK)) {
+		pci_set_consistent_dma_mask(dev, DMA_64BIT_MASK);
+		/* use 64-bit DMA */
+		printk(KERN_DEBUG "Using a 64-bit DMA mask.\n");
+	} else
+#endif
+	if (!pci_set_dma_mask(dev, DMA_32BIT_MASK)) {
+		printk(KERN_DEBUG "Could not set 64-bit DMA mask.\n");
+		pci_set_consistent_dma_mask(dev, DMA_32BIT_MASK);
+		/* 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;
+err_cdev:
+	/* unmap the BARs */
+	unmap_bars(ape, dev);
+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;
+	printk(KERN_DEBUG "remove(0x%p)\n", dev);
+	if ((dev == 0) || (dev->dev.driver_data == 0)) {
+		printk(KERN_DEBUG "remove(dev = 0x%p) dev->dev.driver_data = 0x%p\n", dev, dev->dev.driver_data);
+		return;
+	}
+	ape = (struct ape_dev *)dev->dev.driver_data;
+	printk(KERN_DEBUG "remove(dev = 0x%p) where dev->dev.driver_data = 0x%p\n", dev, ape);
+	if (ape->pci_dev != dev) {
+		printk(KERN_DEBUG "dev->dev.driver_data->pci_dev (0x%08lx) != dev (0x%08lx)\n",
+		(unsigned long)ape->pci_dev, (unsigned long)dev);
+	}
+	/* 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 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 = 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);
+