Staging: udlfb: Support for fbdev mmap clients (defio)

[mirror_ubuntu-zesty-kernel.git] / drivers / staging / udlfb / udlfb.c

/*
 * udlfb.c -- Framebuffer driver for DisplayLink USB controller
 *
 * Copyright (C) 2009 Roberto De Ioris <roberto@unbit.it>
 * Copyright (C) 2009 Jaya Kumar <jayakumar.lkml@gmail.com>
 * Copyright (C) 2009 Bernie Thompson <bernie@plugable.com>
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License v2. See the file COPYING in the main directory of this archive for
 * more details.
 *
 * Layout is based on skeletonfb by James Simmons and Geert Uytterhoeven,
 * usb-skeleton by GregKH.
 *
 * Device-specific portions based on information from Displaylink, with work
 * from Florian Echtler, Henrik Bjerregaard Pedersen, and others.
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/usb.h>
#include <linux/uaccess.h>
#include <linux/mm.h>
#include <linux/fb.h>
#include <linux/vmalloc.h>

#include "udlfb.h"

static struct fb_fix_screeninfo dlfb_fix = {
	.id =           "udlfb",
	.type =         FB_TYPE_PACKED_PIXELS,
	.visual =       FB_VISUAL_TRUECOLOR,
	.xpanstep =     0,
	.ypanstep =     0,
	.ywrapstep =    0,
	.accel =        FB_ACCEL_NONE,
};

static const u32 udlfb_info_flags = FBINFO_DEFAULT | FBINFO_READS_FAST |
#ifdef FBINFO_VIRTFB
		FBINFO_VIRTFB |
#endif
		FBINFO_HWACCEL_IMAGEBLIT | FBINFO_HWACCEL_FILLRECT |
		FBINFO_HWACCEL_COPYAREA | FBINFO_MISC_ALWAYS_SETPAR;

/*
 * There are many DisplayLink-based products, all with unique PIDs. We are able
 * to support all volume ones (circa 2009) with a single driver, so we match
 * globally on VID. TODO: Probe() needs to detect when we might be running
 * "future" chips, and bail on those, so a compatible driver can match.
 */
static struct usb_device_id id_table[] = {
	{.idVendor = 0x17e9, .match_flags = USB_DEVICE_ID_MATCH_VENDOR,},
	{},
};
MODULE_DEVICE_TABLE(usb, id_table);

/* dlfb keeps a list of urbs for efficient bulk transfers */
static void dlfb_urb_completion(struct urb *urb);
static struct urb *dlfb_get_urb(struct dlfb_data *dev);
static int dlfb_submit_urb(struct dlfb_data *dev, struct urb * urb, size_t len);
static int dlfb_alloc_urb_list(struct dlfb_data *dev, int count, size_t size);
static void dlfb_free_urb_list(struct dlfb_data *dev);

/* other symbols with dependents */
#ifdef CONFIG_FB_DEFERRED_IO
static struct fb_deferred_io dlfb_defio;
#endif

/*
 * Inserts a specific DisplayLink controller command into the provided
 * buffer.
 */
static char *dlfb_set_register(char *buf, u8 reg, u8 val)
{
	*buf++ = 0xAF;
	*buf++ = 0x20;
	*buf++ = reg;
	*buf++ = val;
	return buf;
}

static char *dlfb_vidreg_lock(char *buf)
{
	return dlfb_set_register(buf, 0xFF, 0x00);
}

static char *dlfb_vidreg_unlock(char *buf)
{
	return dlfb_set_register(buf, 0xFF, 0xFF);
}

/*
 * On/Off for driving the DisplayLink framebuffer to the display
 */
static char *dlfb_enable_hvsync(char *buf, bool enable)
{
	if (enable)
		return dlfb_set_register(buf, 0x1F, 0x00);
	else
		return dlfb_set_register(buf, 0x1F, 0x01);
}

static char *dlfb_set_color_depth(char *buf, u8 selection)
{
	return dlfb_set_register(buf, 0x00, selection);
}

static char *dlfb_set_base16bpp(char *wrptr, u32 base)
{
	/* the base pointer is 16 bits wide, 0x20 is hi byte. */
	wrptr = dlfb_set_register(wrptr, 0x20, base >> 16);
	wrptr = dlfb_set_register(wrptr, 0x21, base >> 8);
	return dlfb_set_register(wrptr, 0x22, base);
}

static char *dlfb_set_base8bpp(char *wrptr, u32 base)
{
	wrptr = dlfb_set_register(wrptr, 0x26, base >> 16);
	wrptr = dlfb_set_register(wrptr, 0x27, base >> 8);
	return dlfb_set_register(wrptr, 0x28, base);
}

static char *dlfb_set_register_16(char *wrptr, u8 reg, u16 value)
{
	wrptr = dlfb_set_register(wrptr, reg, value >> 8);
	return dlfb_set_register(wrptr, reg+1, value);
}

/*
 * This is kind of weird because the controller takes some
 * register values in a different byte order than other registers.
 */
static char *dlfb_set_register_16be(char *wrptr, u8 reg, u16 value)
{
	wrptr = dlfb_set_register(wrptr, reg, value);
	return dlfb_set_register(wrptr, reg+1, value >> 8);
}

/*
 * LFSR is linear feedback shift register. The reason we have this is
 * because the display controller needs to minimize the clock depth of
 * various counters used in the display path. So this code reverses the
 * provided value into the lfsr16 value by counting backwards to get
 * the value that needs to be set in the hardware comparator to get the
 * same actual count. This makes sense once you read above a couple of
 * times and think about it from a hardware perspective.
 */
static u16 lfsr16(u16 actual_count)
{
	u32 lv = 0xFFFF; /* This is the lfsr value that the hw starts with */

	while (actual_count--) {
		lv =	 ((lv << 1) |
			(((lv >> 15) ^ (lv >> 4) ^ (lv >> 2) ^ (lv >> 1)) & 1))
			& 0xFFFF;
	}

	return (u16) lv;
}

/*
 * This does LFSR conversion on the value that is to be written.
 * See LFSR explanation above for more detail.
 */
static char *dlfb_set_register_lfsr16(char *wrptr, u8 reg, u16 value)
{
	return dlfb_set_register_16(wrptr, reg, lfsr16(value));
}

/*
 * This takes a standard fbdev screeninfo struct and all of its monitor mode
 * details and converts them into the DisplayLink equivalent register commands.
 */
static char *dlfb_set_vid_cmds(char *wrptr, struct fb_var_screeninfo *var)
{
	u16 xds, yds;
	u16 xde, yde;
	u16 yec;

	/* x display start */
	xds = var->left_margin + var->hsync_len;
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x01, xds);
	/* x display end */
	xde = xds + var->xres;
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x03, xde);

	/* y display start */
	yds = var->upper_margin + var->vsync_len;
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x05, yds);
	/* y display end */
	yde = yds + var->yres;
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x07, yde);

	/* x end count is active + blanking - 1 */
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x09,
			xde + var->right_margin - 1);

	/* libdlo hardcodes hsync start to 1 */
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x0B, 1);

	/* hsync end is width of sync pulse + 1 */
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x0D, var->hsync_len + 1);

	/* hpixels is active pixels */
	wrptr = dlfb_set_register_16(wrptr, 0x0F, var->xres);

	/* yendcount is vertical active + vertical blanking */
	yec = var->yres + var->upper_margin + var->lower_margin +
			var->vsync_len;
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x11, yec);

	/* libdlo hardcodes vsync start to 0 */
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x13, 0);

	/* vsync end is width of vsync pulse */
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x15, var->vsync_len);

	/* vpixels is active pixels */
	wrptr = dlfb_set_register_16(wrptr, 0x17, var->yres);

	/* convert picoseconds to 5kHz multiple for pclk5k = x * 1E12/5k */
	wrptr = dlfb_set_register_16be(wrptr, 0x1B,
			200*1000*1000/var->pixclock);

	return wrptr;
}

/*
 * This takes a standard fbdev screeninfo struct that was fetched or prepared
 * and then generates the appropriate command sequence that then drives the
 * display controller.
 */
static int dlfb_set_video_mode(struct dlfb_data *dev,
				struct fb_var_screeninfo *var)
{
	char *buf;
	char *wrptr;
	int retval = 0;
	int writesize;
	struct urb *urb;

	if (!atomic_read(&dev->usb_active))
		return -EPERM;

	urb = dlfb_get_urb(dev);
	if (!urb)
		return -ENOMEM;
	buf = (char *) urb->transfer_buffer;

	/*
	* This first section has to do with setting the base address on the
	* controller * associated with the display. There are 2 base
	* pointers, currently, we only * use the 16 bpp segment.
	*/
	wrptr = dlfb_vidreg_lock(buf);
	wrptr = dlfb_set_color_depth(wrptr, 0x00);
	/* set base for 16bpp segment to 0 */
	wrptr = dlfb_set_base16bpp(wrptr, 0);
	/* set base for 8bpp segment to end of fb */
	wrptr = dlfb_set_base8bpp(wrptr, dev->info->fix.smem_len);

	wrptr = dlfb_set_vid_cmds(wrptr, var);
	wrptr = dlfb_enable_hvsync(wrptr, true);
	wrptr = dlfb_vidreg_unlock(wrptr);

	writesize = wrptr - buf;

	retval = dlfb_submit_urb(dev, urb, writesize);

	return retval;
}

static int dlfb_ops_mmap(struct fb_info *info, struct vm_area_struct *vma)
{
	unsigned long start = vma->vm_start;
	unsigned long size = vma->vm_end - vma->vm_start;
	unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
	unsigned long page, pos;

	printk("MMAP: %lu %u\n", offset + size, info->fix.smem_len);

	if (offset + size > info->fix.smem_len)
		return -EINVAL;

	pos = (unsigned long)info->fix.smem_start + offset;

	while (size > 0) {
		page = vmalloc_to_pfn((void *)pos);
		if (remap_pfn_range(vma, start, page, PAGE_SIZE, PAGE_SHARED))
			return -EAGAIN;

		start += PAGE_SIZE;
		pos += PAGE_SIZE;
		if (size > PAGE_SIZE)
			size -= PAGE_SIZE;
		else
			size = 0;
	}

	vma->vm_flags |= VM_RESERVED;	/* avoid to swap out this VMA */
	return 0;

}

/*
 * Trims identical data from front and back of line
 * Sets new front buffer address and width
 * And returns byte count of identical pixels
 * Assumes CPU natural alignment (unsigned long)
 * for back and front buffer ptrs and width
 */
static int dlfb_trim_hline(const u8 *bback, const u8 **bfront, int *width_bytes)
{
	int j, k;
	const unsigned long *back = (const unsigned long *) bback;
	const unsigned long *front = (const unsigned long *) *bfront;
	const int width = *width_bytes / sizeof(unsigned long);
	int identical = width;
	int start = width;
	int end = width;

	prefetch((void *) front);
	prefetch((void *) back);

	for (j = 0; j < width; j++) {
		if (back[j] != front[j]) {
			start = j;
			break;
		}
	}

	for (k = width - 1; k > j; k--) {
		if (back[k] != front[k]) {
			end = k+1;
			break;
		}
	}

	identical = start + (width - end);
	*bfront = (u8 *) &front[start];
	*width_bytes = (end - start) * sizeof(unsigned long);

	return identical * sizeof(unsigned long);
}

/*
Render a command stream for an encoded horizontal line segment of pixels.

A command buffer holds several commands.
It always begins with a fresh command header
(the protocol doesn't require this, but we enforce it to allow
multiple buffers to be potentially encoded and sent in parallel).
A single command encodes one contiguous horizontal line of pixels

The function relies on the client to do all allocation, so that
rendering can be done directly to output buffers (e.g. USB URBs).
The function fills the supplied command buffer, providing information
on where it left off, so the client may call in again with additional
buffers if the line will take several buffers to complete.

A single command can transmit a maximum of 256 pixels,
regardless of the compression ratio (protocol design limit).
To the hardware, 0 for a size byte means 256

Rather than 256 pixel commands which are either rl or raw encoded,
the rlx command simply assumes alternating raw and rl spans within one cmd.
This has a slightly larger header overhead, but produces more even results.
It also processes all data (read and write) in a single pass.
Performance benchmarks of common cases show it having just slightly better
compression than 256 pixel raw -or- rle commands, with similar CPU consumpion.
But for very rl friendly data, will compress not quite as well.
*/
static void dlfb_compress_hline(
	const uint16_t **pixel_start_ptr,
	const uint16_t *const pixel_end,
	uint32_t *device_address_ptr,
	uint8_t **command_buffer_ptr,
	const uint8_t *const cmd_buffer_end)
{
	const uint16_t *pixel = *pixel_start_ptr;
	uint32_t dev_addr  = *device_address_ptr;
	uint8_t *cmd = *command_buffer_ptr;
	const int bpp = 2;

	while ((pixel_end > pixel) &&
	       (cmd_buffer_end - MIN_RLX_CMD_BYTES > cmd)) {
		uint8_t *raw_pixels_count_byte = 0;
		uint8_t *cmd_pixels_count_byte = 0;
		const uint16_t *raw_pixel_start = 0;
		const uint16_t *cmd_pixel_start, *cmd_pixel_end = 0;
		const uint32_t be_dev_addr = cpu_to_be32(dev_addr);

		prefetchw((void *) cmd); /* pull in one cache line at least */

		*cmd++ = 0xAF;
		*cmd++ = 0x6B;
		*cmd++ = (uint8_t) ((be_dev_addr >> 8) & 0xFF);
		*cmd++ = (uint8_t) ((be_dev_addr >> 16) & 0xFF);
		*cmd++ = (uint8_t) ((be_dev_addr >> 24) & 0xFF);

		cmd_pixels_count_byte = cmd++; /*  we'll know this later */
		cmd_pixel_start = pixel;

		raw_pixels_count_byte = cmd++; /*  we'll know this later */
		raw_pixel_start = pixel;

		cmd_pixel_end = pixel + min(MAX_CMD_PIXELS + 1,
			min((int)(pixel_end - pixel),
			    (int)(cmd_buffer_end - cmd) / bpp));

		prefetch_range((void *) pixel, (cmd_pixel_end - pixel) * bpp);

		while (pixel < cmd_pixel_end) {
			const uint16_t * const repeating_pixel = pixel;

			*(uint16_t *)cmd = cpu_to_be16p(pixel);
			cmd += 2;
			pixel++;

			if (unlikely((pixel < cmd_pixel_end) &&
				     (*pixel == *repeating_pixel))) {
				/* go back and fill in raw pixel count */
				*raw_pixels_count_byte = ((repeating_pixel -
						raw_pixel_start) + 1) & 0xFF;

				while ((pixel < cmd_pixel_end)
				       && (*pixel == *repeating_pixel)) {
					pixel++;
				}

				/* immediately after raw data is repeat byte */
				*cmd++ = ((pixel - repeating_pixel) - 1) & 0xFF;

				/* Then start another raw pixel span */
				raw_pixel_start = pixel;
				raw_pixels_count_byte = cmd++;
			}
		}

		if (pixel > raw_pixel_start) {
			/* finalize last RAW span */
			*raw_pixels_count_byte = (pixel-raw_pixel_start) & 0xFF;
		}

		*cmd_pixels_count_byte = (pixel - cmd_pixel_start) & 0xFF;
		dev_addr += (pixel - cmd_pixel_start) * bpp;
	}

	if (cmd_buffer_end <= MIN_RLX_CMD_BYTES + cmd) {
		/* Fill leftover bytes with no-ops */
		if (cmd_buffer_end > cmd)
			memset(cmd, 0xAF, cmd_buffer_end - cmd);
		cmd = (uint8_t *) cmd_buffer_end;
	}

	*command_buffer_ptr = cmd;
	*pixel_start_ptr = pixel;
	*device_address_ptr = dev_addr;

	return;
}

/*
 * There are 3 copies of every pixel: The front buffer that the fbdev
 * client renders to, the actual framebuffer across the USB bus in hardware
 * (that we can only write to, slowly, and can never read), and (optionally)
 * our shadow copy that tracks what's been sent to that hardware buffer.
 */
static void dlfb_render_hline(struct dlfb_data *dev, struct urb **urb_ptr,
			      const char *front, char **urb_buf_ptr,
			      u32 byte_offset, u32 byte_width,
			      int *ident_ptr, int *sent_ptr)
{
	const u8 *line_start, *line_end, *next_pixel;
	u32 dev_addr = dev->base16 + byte_offset;
	struct urb *urb = *urb_ptr;
	u8 *cmd = *urb_buf_ptr;
	u8 *cmd_end = (u8 *) urb->transfer_buffer + urb->transfer_buffer_length;

	line_start = (u8 *) (front + byte_offset);
	next_pixel = line_start;
	line_end = next_pixel + byte_width;

	if (dev->backing_buffer) {
		int offset;
		const u8 *back_start = (u8 *) (dev->backing_buffer
						+ byte_offset);

		*ident_ptr += dlfb_trim_hline(back_start, &next_pixel,
			&byte_width);

		offset = next_pixel - line_start;
		line_end = next_pixel + byte_width;
		dev_addr += offset;
		back_start += offset;
		line_start += offset;

		memcpy((char *)back_start, (char *) line_start,
		       byte_width);
	}

	while (next_pixel < line_end) {

		dlfb_compress_hline((const uint16_t **) &next_pixel,
			     (const uint16_t *) line_end, &dev_addr,
			(u8 **) &cmd, (u8 *) cmd_end);

		if (cmd >= cmd_end) {
			int len = cmd - (u8 *) urb->transfer_buffer;
			if (dlfb_submit_urb(dev, urb, len))
				return; /* lost pixels is set */
			*sent_ptr += len;
			urb = dlfb_get_urb(dev);
			if (!urb)
				return; /* lost_pixels is set */
			*urb_ptr = urb;
			cmd = urb->transfer_buffer;
			cmd_end = &cmd[urb->transfer_buffer_length];
		}
	}

	*urb_buf_ptr = cmd;
}

int dlfb_handle_damage(struct dlfb_data *dev, int x, int y,
	       int width, int height, char *data)
{
	int i, ret;
	char *cmd;
	cycles_t start_cycles, end_cycles;
	int bytes_sent = 0;
	int bytes_identical = 0;
	struct urb *urb;
	int aligned_x;

	start_cycles = get_cycles();

	aligned_x = DL_ALIGN_DOWN(x, sizeof(unsigned long));
	width = DL_ALIGN_UP(width + (x-aligned_x), sizeof(unsigned long));
	x = aligned_x;

	if ((width <= 0) ||
	    (x + width > dev->info->var.xres) ||
	    (y + height > dev->info->var.yres))
		return -EINVAL;

	if (!atomic_read(&dev->usb_active))
		return 0;

	urb = dlfb_get_urb(dev);
	if (!urb)
		return 0;
	cmd = urb->transfer_buffer;

	for (i = y; i < y + height ; i++) {
		const int line_offset = dev->info->fix.line_length * i;
		const int byte_offset = line_offset + (x * BPP);

		dlfb_render_hline(dev, &urb, (char *) dev->info->fix.smem_start,
				  &cmd, byte_offset, width * BPP,
				  &bytes_identical, &bytes_sent);
	}

	if (cmd > (char *) urb->transfer_buffer) {
		/* Send partial buffer remaining before exiting */
		int len = cmd - (char *) urb->transfer_buffer;
		ret = dlfb_submit_urb(dev, urb, len);
		bytes_sent += len;
	} else
		dlfb_urb_completion(urb);

	atomic_add(bytes_sent, &dev->bytes_sent);
	atomic_add(bytes_identical, &dev->bytes_identical);
	atomic_add(width*height*2, &dev->bytes_rendered);
	end_cycles = get_cycles();
	atomic_add(((unsigned int) ((end_cycles - start_cycles)
		    >> 10)), /* Kcycles */
		   &dev->cpu_kcycles_used);

	return 0;
}

/* hardware has native COPY command (see libdlo), but not worth it for fbcon */
static void dlfb_ops_copyarea(struct fb_info *info,
				const struct fb_copyarea *area)
{

	struct dlfb_data *dev = info->par;

#if defined CONFIG_FB_SYS_COPYAREA || defined CONFIG_FB_SYS_COPYAREA_MODULE

	sys_copyarea(info, area);

	dlfb_handle_damage(dev, area->dx, area->dy,
			area->width, area->height, info->screen_base);
#endif
	atomic_inc(&dev->copy_count);

}

static void dlfb_ops_imageblit(struct fb_info *info,
				const struct fb_image *image)
{
	struct dlfb_data *dev = info->par;

#if defined CONFIG_FB_SYS_IMAGEBLIT || defined CONFIG_FB_SYS_IMAGEBLIT_MODULE

	sys_imageblit(info, image);

	dlfb_handle_damage(dev, image->dx, image->dy,
			image->width, image->height, info->screen_base);

#endif

	atomic_inc(&dev->blit_count);
}

static void dlfb_ops_fillrect(struct fb_info *info,
			  const struct fb_fillrect *rect)
{
	struct dlfb_data *dev = info->par;

#if defined CONFIG_FB_SYS_FILLRECT || defined CONFIG_FB_SYS_FILLRECT_MODULE

	sys_fillrect(info, rect);

	dlfb_handle_damage(dev, rect->dx, rect->dy, rect->width,
			      rect->height, info->screen_base);
#endif

	atomic_inc(&dev->fill_count);

}

static void dlfb_get_edid(struct dlfb_data *dev)
{
	int i;
	int ret;
	char rbuf[2];

	for (i = 0; i < sizeof(dev->edid); i++) {
		ret = usb_control_msg(dev->udev,
				    usb_rcvctrlpipe(dev->udev, 0), (0x02),
				    (0x80 | (0x02 << 5)), i << 8, 0xA1, rbuf, 2,
				    0);
		dev->edid[i] = rbuf[1];
	}
}

static int dlfb_ops_ioctl(struct fb_info *info, unsigned int cmd,
				unsigned long arg)
{

	struct dlfb_data *dev = info->par;
	struct dloarea *area = NULL;

	if (!atomic_read(&dev->usb_active))
		return 0;

	/* TODO: Update X server to get this from sysfs instead */
	if (cmd == DLFB_IOCTL_RETURN_EDID) {
		char *edid = (char *)arg;
		dlfb_get_edid(dev);
		if (copy_to_user(edid, dev->edid, sizeof(dev->edid)))
			return -EFAULT;
		return 0;
	}

	/* TODO: Help propose a standard fb.h ioctl to report mmap damage */
	if (cmd == DLFB_IOCTL_REPORT_DAMAGE) {

		area = (struct dloarea *)arg;

		if (area->x < 0)
			area->x = 0;

		if (area->x > info->var.xres)
			area->x = info->var.xres;

		if (area->y < 0)
			area->y = 0;

		if (area->y > info->var.yres)
			area->y = info->var.yres;

		atomic_set(&dev->use_defio, 0);

		dlfb_handle_damage(dev, area->x, area->y, area->w, area->h,
			   info->screen_base);
		atomic_inc(&dev->damage_count);
	}

	return 0;
}

/* taken from vesafb */
static int
dlfb_ops_setcolreg(unsigned regno, unsigned red, unsigned green,
	       unsigned blue, unsigned transp, struct fb_info *info)
{
	int err = 0;

	if (regno >= info->cmap.len)
		return 1;

	if (regno < 16) {
		if (info->var.red.offset == 10) {
			/* 1:5:5:5 */
			((u32 *) (info->pseudo_palette))[regno] =
			    ((red & 0xf800) >> 1) |
			    ((green & 0xf800) >> 6) | ((blue & 0xf800) >> 11);
		} else {
			/* 0:5:6:5 */
			((u32 *) (info->pseudo_palette))[regno] =
			    ((red & 0xf800)) |
			    ((green & 0xfc00) >> 5) | ((blue & 0xf800) >> 11);
		}
	}

	return err;
}

/*
 * It's common for several clients to have framebuffer open simultaneously.
 * e.g. both fbcon and X. Makes things interesting.
 */
static int dlfb_ops_open(struct fb_info *info, int user)
{
	struct dlfb_data *dev = info->par;

/*	if (user == 0)
 *		We could special case kernel mode clients (fbcon) here
 */

	mutex_lock(&dev->fb_open_lock);

	dev->fb_count++;

#ifdef CONFIG_FB_DEFERRED_IO
	if ((atomic_read(&dev->use_defio)) && (info->fbdefio == NULL)) {
		/* enable defio */
		info->fbdefio = &dlfb_defio;
		fb_deferred_io_init(info);
	}
#endif

	dl_notice("open /dev/fb%d user=%d fb_info=%p count=%d\n",
	    info->node, user, info, dev->fb_count);

	mutex_unlock(&dev->fb_open_lock);

	return 0;
}

static int dlfb_ops_release(struct fb_info *info, int user)
{
	struct dlfb_data *dev = info->par;

	mutex_lock(&dev->fb_open_lock);

	dev->fb_count--;

#ifdef CONFIG_FB_DEFERRED_IO
	if ((dev->fb_count == 0) && (info->fbdefio)) {
		fb_deferred_io_cleanup(info);
		info->fbdefio = NULL;
		info->fbops->fb_mmap = dlfb_ops_mmap;
	}
#endif

	dl_notice("release /dev/fb%d user=%d count=%d\n",
		  info->node, user, dev->fb_count);

	mutex_unlock(&dev->fb_open_lock);

	return 0;
}

/*
 * Called when all client interfaces to start transactions have been disabled,
 * and all references to our device instance (dlfb_data) are released.
 * Every transaction must have a reference, so we know are fully spun down
 */
static void dlfb_delete(struct kref *kref)
{
	struct dlfb_data *dev = container_of(kref, struct dlfb_data, kref);

	if (dev->backing_buffer)
		vfree(dev->backing_buffer);

	mutex_destroy(&dev->fb_open_lock);

	kfree(dev);
}

/*
 * Called by fbdev as last part of unregister_framebuffer() process
 * No new clients can open connections. Deallocate everything fb_info.
 */
static void dlfb_ops_destroy(struct fb_info *info)
{
	struct dlfb_data *dev = info->par;

	if (info->cmap.len != 0)
		fb_dealloc_cmap(&info->cmap);
	if (info->monspecs.modedb)
		fb_destroy_modedb(info->monspecs.modedb);
	if (info->screen_base)
		vfree(info->screen_base);

	fb_destroy_modelist(&info->modelist);

	framebuffer_release(info);

	/* ref taken before register_framebuffer() for dlfb_data clients */
	kref_put(&dev->kref, dlfb_delete);
}

/*
 * Check whether a video mode is supported by the DisplayLink chip
 * We start from monitor's modes, so don't need to filter that here
 */
static int dlfb_is_valid_mode(struct fb_videomode *mode,
		struct fb_info *info)
{
	struct dlfb_data *dev = info->par;

	if (mode->xres * mode->yres > dev->sku_pixel_limit)
		return 0;

	return 1;
}

static void dlfb_var_color_format(struct fb_var_screeninfo *var)
{
	const struct fb_bitfield red = { 11, 5, 0 };
	const struct fb_bitfield green = { 5, 6, 0 };
	const struct fb_bitfield blue = { 0, 5, 0 };

	var->bits_per_pixel = 16;
	var->red = red;
	var->green = green;
	var->blue = blue;
}

static int dlfb_ops_check_var(struct fb_var_screeninfo *var,
				struct fb_info *info)
{
	struct fb_videomode mode;

	/* TODO: support dynamically changing framebuffer size */
	if ((var->xres * var->yres * 2) > info->fix.smem_len)
		return -EINVAL;

	/* set device-specific elements of var unrelated to mode */
	dlfb_var_color_format(var);

	fb_var_to_videomode(&mode, var);

	if (!dlfb_is_valid_mode(&mode, info))
		return -EINVAL;

	return 0;
}

static int dlfb_ops_set_par(struct fb_info *info)
{
	struct dlfb_data *dev = info->par;

	dl_notice("set_par mode %dx%d\n", info->var.xres, info->var.yres);

	return dlfb_set_video_mode(dev, &info->var);
}

static int dlfb_ops_blank(int blank_mode, struct fb_info *info)
{
	struct dlfb_data *dev = info->par;
	char *bufptr;
	struct urb *urb;

	urb = dlfb_get_urb(dev);
	if (!urb)
		return 0;
	bufptr = (char *) urb->transfer_buffer;

	/* overloading usb_active.  UNBLANK can conflict with teardown */

	bufptr = dlfb_vidreg_lock(bufptr);
	if (blank_mode != FB_BLANK_UNBLANK) {
		atomic_set(&dev->usb_active, 0);
		bufptr = dlfb_enable_hvsync(bufptr, false);
	} else {
		atomic_set(&dev->usb_active, 1);
		bufptr = dlfb_enable_hvsync(bufptr, true);
	}
	bufptr = dlfb_vidreg_unlock(bufptr);

	dlfb_submit_urb(dev, urb, bufptr - (char *) urb->transfer_buffer);

	return 0;
}

static struct fb_ops dlfb_ops = {
	.owner = THIS_MODULE,
	.fb_setcolreg = dlfb_ops_setcolreg,
	.fb_fillrect = dlfb_ops_fillrect,
	.fb_copyarea = dlfb_ops_copyarea,
	.fb_imageblit = dlfb_ops_imageblit,
	.fb_mmap = dlfb_ops_mmap,
	.fb_ioctl = dlfb_ops_ioctl,
	.fb_open = dlfb_ops_open,
	.fb_release = dlfb_ops_release,
	.fb_blank = dlfb_ops_blank,
	.fb_check_var = dlfb_ops_check_var,
	.fb_set_par = dlfb_ops_set_par,
};

/*
 * Calls dlfb_get_edid() to query the EDID of attached monitor via usb cmds
 * Then parses EDID into three places used by various parts of fbdev:
 * fb_var_screeninfo contains the timing of the monitor's preferred mode
 * fb_info.monspecs is full parsed EDID info, including monspecs.modedb
 * fb_info.modelist is a linked list of all monitor & VESA modes which work
 *
 * If EDID is not readable/valid, then modelist is all VESA modes,
 * monspecs is NULL, and fb_var_screeninfo is set to safe VESA mode
 * Returns 0 if EDID parses successfully
 */
static int dlfb_parse_edid(struct dlfb_data *dev,
			    struct fb_var_screeninfo *var,
			    struct fb_info *info)
{
	int i;
	const struct fb_videomode *default_vmode = NULL;
	int result = 0;

	fb_destroy_modelist(&info->modelist);
	memset(&info->monspecs, 0, sizeof(info->monspecs));

	dlfb_get_edid(dev);
	fb_edid_to_monspecs(dev->edid, &info->monspecs);

	if (info->monspecs.modedb_len > 0) {

		for (i = 0; i < info->monspecs.modedb_len; i++) {
			if (dlfb_is_valid_mode(&info->monspecs.modedb[i], info))
				fb_add_videomode(&info->monspecs.modedb[i],
					&info->modelist);
		}

		default_vmode = fb_find_best_display(&info->monspecs,
						     &info->modelist);
	} else {
		struct fb_videomode fb_vmode = {0};

		dl_err("Unable to get valid EDID from device/display\n");
		result = 1;

		/*
		 * Add the standard VESA modes to our modelist
		 * Since we don't have EDID, there may be modes that
		 * overspec monitor and/or are incorrect aspect ratio, etc.
		 * But at least the user has a chance to choose
		 */
		for (i = 0; i < VESA_MODEDB_SIZE; i++) {
			if (dlfb_is_valid_mode((struct fb_videomode *)
						&vesa_modes[i], info))
				fb_add_videomode(&vesa_modes[i],
						 &info->modelist);
		}

		/*
		 * default to resolution safe for projectors
		 * (since they are most common case without EDID)
		 */
		fb_vmode.xres = 800;
		fb_vmode.yres = 600;
		fb_vmode.refresh = 60;
		default_vmode = fb_find_nearest_mode(&fb_vmode,
						     &info->modelist);
	}

	fb_videomode_to_var(var, default_vmode);
	dlfb_var_color_format(var);

	return result;
}

static ssize_t metrics_bytes_rendered_show(struct device *fbdev,
				   struct device_attribute *a, char *buf) {
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;
	return snprintf(buf, PAGE_SIZE, "%u\n",
			atomic_read(&dev->bytes_rendered));
}

static ssize_t metrics_bytes_identical_show(struct device *fbdev,
				   struct device_attribute *a, char *buf) {
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;
	return snprintf(buf, PAGE_SIZE, "%u\n",
			atomic_read(&dev->bytes_identical));
}

static ssize_t metrics_bytes_sent_show(struct device *fbdev,
				   struct device_attribute *a, char *buf) {
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;
	return snprintf(buf, PAGE_SIZE, "%u\n",
			atomic_read(&dev->bytes_sent));
}

static ssize_t metrics_cpu_kcycles_used_show(struct device *fbdev,
				   struct device_attribute *a, char *buf) {
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;
	return snprintf(buf, PAGE_SIZE, "%u\n",
			atomic_read(&dev->cpu_kcycles_used));
}

static ssize_t metrics_misc_show(struct device *fbdev,
				   struct device_attribute *a, char *buf) {
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;
	return snprintf(buf, PAGE_SIZE,
			"Calls to\ndamage: %u\nblit: %u\n"
			"defio faults: %u\ncopy: %u\n"
			"fill: %u\n\n"
			"active framebuffer clients: %d\n"
			"urbs available %d(%d)\n"
			"Shadow framebuffer in use? %s\n"
			"Any lost pixels? %s\n",
			atomic_read(&dev->damage_count),
			atomic_read(&dev->blit_count),
			atomic_read(&dev->defio_fault_count),
			atomic_read(&dev->copy_count),
			atomic_read(&dev->fill_count),
			dev->fb_count,
			dev->urbs.available, dev->urbs.limit_sem.count,
			(dev->backing_buffer) ? "yes" : "no",
			atomic_read(&dev->lost_pixels) ? "yes" : "no");
}

static ssize_t edid_show(struct kobject *kobj, struct bin_attribute *a,
			 char *buf, loff_t off, size_t count) {
	struct device *fbdev = container_of(kobj, struct device, kobj);
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;
	char *edid = &dev->edid[0];
	const size_t size = sizeof(dev->edid);

	if (dlfb_parse_edid(dev, &fb_info->var, fb_info))
		return 0;

	if (off >= size)
		return 0;

	if (off + count > size)
		count = size - off;
	memcpy(buf, edid + off, count);

	return count;
}


static ssize_t metrics_reset_store(struct device *fbdev,
			   struct device_attribute *attr,
			   const char *buf, size_t count)
{
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;

	atomic_set(&dev->bytes_rendered, 0);
	atomic_set(&dev->bytes_identical, 0);
	atomic_set(&dev->bytes_sent, 0);
	atomic_set(&dev->cpu_kcycles_used, 0);
	atomic_set(&dev->blit_count, 0);
	atomic_set(&dev->copy_count, 0);
	atomic_set(&dev->fill_count, 0);
	atomic_set(&dev->defio_fault_count, 0);
	atomic_set(&dev->damage_count, 0);

	return count;
}

static ssize_t use_defio_show(struct device *fbdev,
				   struct device_attribute *a, char *buf) {
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;
	return snprintf(buf, PAGE_SIZE, "%d\n",
			atomic_read(&dev->use_defio));
}

static ssize_t use_defio_store(struct device *fbdev,
			   struct device_attribute *attr,
			   const char *buf, size_t count)
{
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;

	if (count > 0) {
		if (buf[0] == '0')
			atomic_set(&dev->use_defio, 0);
		if (buf[0] == '1')
			atomic_set(&dev->use_defio, 1);
	}
	return count;
}

static struct bin_attribute edid_attr = {
	.attr.name = "edid",
	.attr.mode = 0444,
	.size = 128,
	.read = edid_show,
};

static struct device_attribute fb_device_attrs[] = {
	__ATTR_RO(metrics_bytes_rendered),
	__ATTR_RO(metrics_bytes_identical),
	__ATTR_RO(metrics_bytes_sent),
	__ATTR_RO(metrics_cpu_kcycles_used),
	__ATTR_RO(metrics_misc),
	__ATTR(metrics_reset, S_IWUGO, NULL, metrics_reset_store),
	__ATTR_RW(use_defio),
};

#ifdef CONFIG_FB_DEFERRED_IO
static void dlfb_dpy_deferred_io(struct fb_info *info,
				struct list_head *pagelist)
{
	struct page *cur;
	struct fb_deferred_io *fbdefio = info->fbdefio;
	struct dlfb_data *dev = info->par;
	struct urb *urb;
	char *cmd;
	cycles_t start_cycles, end_cycles;
	int bytes_sent = 0;
	int bytes_identical = 0;
	int bytes_rendered = 0;
	int fault_count = 0;

	if (!atomic_read(&dev->use_defio))
		return;

	if (!atomic_read(&dev->usb_active))
		return;

	start_cycles = get_cycles();

	urb = dlfb_get_urb(dev);
	if (!urb)
		return;
	cmd = urb->transfer_buffer;

	/* walk the written page list and render each to device */
	list_for_each_entry(cur, &fbdefio->pagelist, lru) {
		dlfb_render_hline(dev, &urb, (char *) info->fix.smem_start,
				  &cmd, cur->index << PAGE_SHIFT,
				  PAGE_SIZE, &bytes_identical, &bytes_sent);
		bytes_rendered += PAGE_SIZE;
		fault_count++;
	}

	if (cmd > (char *) urb->transfer_buffer) {
		/* Send partial buffer remaining before exiting */
		int len = cmd - (char *) urb->transfer_buffer;
		dlfb_submit_urb(dev, urb, len);
		bytes_sent += len;
	} else
		dlfb_urb_completion(urb);

	atomic_add(fault_count, &dev->defio_fault_count);
	atomic_add(bytes_sent, &dev->bytes_sent);
	atomic_add(bytes_identical, &dev->bytes_identical);
	atomic_add(bytes_rendered, &dev->bytes_rendered);
	end_cycles = get_cycles();
	atomic_add(((unsigned int) ((end_cycles - start_cycles)
		    >> 10)), /* Kcycles */
		   &dev->cpu_kcycles_used);
}

static struct fb_deferred_io dlfb_defio = {
	.delay          = 5,
	.deferred_io    = dlfb_dpy_deferred_io,
};

#endif

/*
 * This is necessary before we can communicate with the display controller.
 */
static int dlfb_select_std_channel(struct dlfb_data *dev)
{
	int ret;
	u8 set_def_chn[] = {	   0x57, 0xCD, 0xDC, 0xA7,
				0x1C, 0x88, 0x5E, 0x15,
				0x60, 0xFE, 0xC6, 0x97,
				0x16, 0x3D, 0x47, 0xF2  };

	ret = usb_control_msg(dev->udev, usb_sndctrlpipe(dev->udev, 0),
			NR_USB_REQUEST_CHANNEL,
			(USB_DIR_OUT | USB_TYPE_VENDOR), 0, 0,
			set_def_chn, sizeof(set_def_chn), USB_CTRL_SET_TIMEOUT);
	return ret;
}


static int dlfb_usb_probe(struct usb_interface *interface,
			const struct usb_device_id *id)
{
	struct usb_device *usbdev;
	struct dlfb_data *dev;
	struct fb_info *info;
	int videomemorysize;
	int i;
	unsigned char *videomemory;
	int retval = -ENOMEM;
	struct fb_var_screeninfo *var;
	int registered = 0;
	u16 *pix_framebuffer;

	/* usb initialization */

	usbdev = interface_to_usbdev(interface);

	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
	if (dev == NULL) {
		err("dlfb_usb_probe: failed alloc of dev struct\n");
		goto error;
	}

	/* we need to wait for both usb and fbdev to spin down on disconnect */
	kref_init(&dev->kref); /* matching kref_put in usb .disconnect fn */
	kref_get(&dev->kref); /* matching kref_put in .fb_destroy function*/

	dev->udev = usbdev;
	dev->gdev = &usbdev->dev; /* our generic struct device * */
	usb_set_intfdata(interface, dev);

	if (!dlfb_alloc_urb_list(dev, WRITES_IN_FLIGHT, MAX_TRANSFER)) {
		retval = -ENOMEM;
		dl_err("dlfb_alloc_urb_list failed\n");
		goto error;
	}

	mutex_init(&dev->fb_open_lock);

	/* We don't register a new USB class. Our client interface is fbdev */

	/* allocates framebuffer driver structure, not framebuffer memory */
	info = framebuffer_alloc(0, &usbdev->dev);
	if (!info) {
		retval = -ENOMEM;
		dl_err("framebuffer_alloc failed\n");
		goto error;
	}
	dev->info = info;
	info->par = dev;
	info->pseudo_palette = dev->pseudo_palette;
	info->fbops = &dlfb_ops;

	var = &info->var;

	/* TODO set limit based on actual SKU detection */
	dev->sku_pixel_limit = 2048 * 1152;

	INIT_LIST_HEAD(&info->modelist);
	dlfb_parse_edid(dev, var, info);

	/*
	 * ok, now that we've got the size info, we can alloc our framebuffer.
	 */
	info->fix = dlfb_fix;
	info->fix.line_length = var->xres * (var->bits_per_pixel / 8);
	videomemorysize = info->fix.line_length * var->yres;

	/*
	 * The big chunk of system memory we use as a virtual framebuffer.
	 * TODO: Handle fbcon cursor code calling blit in interrupt context
	 */
	videomemory = vmalloc(videomemorysize);
	if (!videomemory) {
		retval = -ENOMEM;
		dl_err("Virtual framebuffer alloc failed\n");
		goto error;
	}

	info->screen_base = videomemory;
	info->fix.smem_len = PAGE_ALIGN(videomemorysize);
	info->fix.smem_start = (unsigned long) videomemory;
	info->flags = udlfb_info_flags;


	/*
	 * Second framebuffer copy, mirroring the state of the framebuffer
	 * on the physical USB device. We can function without this.
	 * But with imperfect damage info we may end up sending pixels over USB
	 * that were, in fact, unchanged -- wasting limited USB bandwidth
	 */
	dev->backing_buffer = vmalloc(videomemorysize);
	if (!dev->backing_buffer)
		dl_warn("No shadow/backing buffer allcoated\n");
	else
		memset(dev->backing_buffer, 0, videomemorysize);

	retval = fb_alloc_cmap(&info->cmap, 256, 0);
	if (retval < 0) {
		dl_err("fb_alloc_cmap failed %x\n", retval);
		goto error;
	}

	/* ready to begin using device */

#ifdef CONFIG_FB_DEFERRED_IO
	atomic_set(&dev->use_defio, 1);
#endif
	atomic_set(&dev->usb_active, 1);
	dlfb_select_std_channel(dev);

	dlfb_ops_check_var(var, info);
	dlfb_ops_set_par(info);

	/* paint greenscreen */
	pix_framebuffer = (u16 *) videomemory;
	for (i = 0; i < videomemorysize / 2; i++)
		pix_framebuffer[i] = 0x37e6;

	dlfb_handle_damage(dev, 0, 0, info->var.xres, info->var.yres,
				videomemory);

	retval = register_framebuffer(info);
	if (retval < 0) {
		dl_err("register_framebuffer failed %d\n", retval);
		goto error;
	}
	registered = 1;

	for (i = 0; i < ARRAY_SIZE(fb_device_attrs); i++)
		device_create_file(info->dev, &fb_device_attrs[i]);

	device_create_bin_file(info->dev, &edid_attr);

	dl_err("DisplayLink USB device /dev/fb%d attached. %dx%d resolution."
			" Using %dK framebuffer memory\n", info->node,
			var->xres, var->yres,
			((dev->backing_buffer) ?
			videomemorysize * 2 : videomemorysize) >> 10);
	return 0;

error:
	if (dev) {
		if (registered) {
			unregister_framebuffer(info);
			dlfb_ops_destroy(info);
		} else
			kref_put(&dev->kref, dlfb_delete);

		if (dev->urbs.count > 0)
			dlfb_free_urb_list(dev);
		kref_put(&dev->kref, dlfb_delete); /* last ref from kref_init */

		/* dev has been deallocated. Do not dereference */
	}

	return retval;
}

static void dlfb_usb_disconnect(struct usb_interface *interface)
{
	struct dlfb_data *dev;
	struct fb_info *info;
	int i;

	dev = usb_get_intfdata(interface);
	info = dev->info;

	/* when non-active we'll update virtual framebuffer, but no new urbs */
	atomic_set(&dev->usb_active, 0);

	usb_set_intfdata(interface, NULL);

	for (i = 0; i < ARRAY_SIZE(fb_device_attrs); i++)
		device_remove_file(info->dev, &fb_device_attrs[i]);

	device_remove_bin_file(info->dev, &edid_attr);

	/* this function will wait for all in-flight urbs to complete */
	dlfb_free_urb_list(dev);

	if (info) {
		dl_notice("Detaching /dev/fb%d\n", info->node);
		unregister_framebuffer(info);
		dlfb_ops_destroy(info);
	}

	/* release reference taken by kref_init in probe() */
	kref_put(&dev->kref, dlfb_delete);

	/* consider dlfb_data freed */

	return;
}

static struct usb_driver dlfb_driver = {
	.name = "udlfb",
	.probe = dlfb_usb_probe,
	.disconnect = dlfb_usb_disconnect,
	.id_table = id_table,
};

static int __init dlfb_module_init(void)
{
	int res;

	res = usb_register(&dlfb_driver);
	if (res)
		err("usb_register failed. Error number %d", res);

	printk("VMODES initialized\n");

	return res;
}

static void __exit dlfb_module_exit(void)
{
	usb_deregister(&dlfb_driver);
}

module_init(dlfb_module_init);
module_exit(dlfb_module_exit);

static void dlfb_urb_completion(struct urb *urb)
{
	struct urb_node *unode = urb->context;
	struct dlfb_data *dev = unode->dev;
	unsigned long flags;

	/* sync/async unlink faults aren't errors */
	if (urb->status) {
		if (!(urb->status == -ENOENT ||
		    urb->status == -ECONNRESET ||
		    urb->status == -ESHUTDOWN)) {
			dl_err("%s - nonzero write bulk status received: %d\n",
				__func__, urb->status);
			atomic_set(&dev->lost_pixels, 1);
		}
	}

	urb->transfer_buffer_length = dev->urbs.size; /* reset to actual */

	spin_lock_irqsave(&dev->urbs.lock, flags);
	list_add_tail(&unode->entry, &dev->urbs.list);
	dev->urbs.available++;
	spin_unlock_irqrestore(&dev->urbs.lock, flags);

	up(&dev->urbs.limit_sem);
}

static void dlfb_free_urb_list(struct dlfb_data *dev)
{
	int count = dev->urbs.count;
	struct list_head *node;
	struct urb_node *unode;
	struct urb *urb;
	int ret;
	unsigned long flags;

	dl_notice("Waiting for completes and freeing all render urbs\n");

	/* keep waiting and freeing, until we've got 'em all */
	while (count--) {
		/* Timeout means a memory leak and/or fault */
		ret = down_timeout(&dev->urbs.limit_sem, FREE_URB_TIMEOUT);
		if (ret) {
			BUG_ON(ret);
			break;
		}
		spin_lock_irqsave(&dev->urbs.lock, flags);

		node = dev->urbs.list.next; /* have reserved one with sem */
		list_del_init(node);

		spin_unlock_irqrestore(&dev->urbs.lock, flags);

		unode = list_entry(node, struct urb_node, entry);
		urb = unode->urb;

		/* Free each separately allocated piece */
		usb_buffer_free(urb->dev, dev->urbs.size,
			urb->transfer_buffer, urb->transfer_dma);
		usb_free_urb(urb);
		kfree(node);
	}

	kref_put(&dev->kref, dlfb_delete);

}

static int dlfb_alloc_urb_list(struct dlfb_data *dev, int count, size_t size)
{
	int i = 0;
	struct urb *urb;
	struct urb_node *unode;
	char *buf;

	spin_lock_init(&dev->urbs.lock);

	dev->urbs.size = size;
	INIT_LIST_HEAD(&dev->urbs.list);

	while (i < count) {
		unode = kzalloc(sizeof(struct urb_node), GFP_KERNEL);
		if (!unode)
			break;
		unode->dev = dev;

		urb = usb_alloc_urb(0, GFP_KERNEL);
		if (!urb) {
			kfree(unode);
			break;
		}
		unode->urb = urb;

		buf = usb_buffer_alloc(dev->udev, MAX_TRANSFER, GFP_KERNEL,
					&urb->transfer_dma);
		if (!buf) {
			kfree(unode);
			usb_free_urb(urb);
			break;
		}

		/* urb->transfer_buffer_length set to actual before submit */
		usb_fill_bulk_urb(urb, dev->udev, usb_sndbulkpipe(dev->udev, 1),
			buf, size, dlfb_urb_completion, unode);
		urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;

		list_add_tail(&unode->entry, &dev->urbs.list);

		i++;
	}

	sema_init(&dev->urbs.limit_sem, i);
	dev->urbs.count = i;
	dev->urbs.available = i;

	kref_get(&dev->kref); /* released in free_render_urbs() */

	dl_notice("allocated %d %d byte urbs \n", i, (int) size);

	return i;
}

static struct urb *dlfb_get_urb(struct dlfb_data *dev)
{
	int ret = 0;
	struct list_head *entry;
	struct urb_node *unode;
	struct urb *urb = NULL;
	unsigned long flags;

	/* Wait for an in-flight buffer to complete and get re-queued */
	ret = down_timeout(&dev->urbs.limit_sem, GET_URB_TIMEOUT);
	if (ret) {
		atomic_set(&dev->lost_pixels, 1);
		dl_err("wait for urb interrupted: %x\n", ret);
		goto error;
	}

	spin_lock_irqsave(&dev->urbs.lock, flags);

	BUG_ON(list_empty(&dev->urbs.list)); /* reserved one with limit_sem */
	entry = dev->urbs.list.next;
	list_del_init(entry);
	dev->urbs.available--;

	spin_unlock_irqrestore(&dev->urbs.lock, flags);

	unode = list_entry(entry, struct urb_node, entry);
	urb = unode->urb;

error:
	return urb;
}

static int dlfb_submit_urb(struct dlfb_data *dev, struct urb *urb, size_t len)
{
	int ret;

	BUG_ON(len > dev->urbs.size);

	urb->transfer_buffer_length = len; /* set to actual payload len */
	ret = usb_submit_urb(urb, GFP_KERNEL);
	if (ret) {
		dlfb_urb_completion(urb); /* because no one else will */
		atomic_set(&dev->lost_pixels, 1);
		dl_err("usb_submit_urb error %x\n", ret);
	}
	return ret;
}

MODULE_AUTHOR("Roberto De Ioris <roberto@unbit.it>, "
	      "Jaya Kumar <jayakumar.lkml@gmail.com>, "
	      "Bernie Thompson <bernie@plugable.com>");
MODULE_DESCRIPTION("DisplayLink kernel framebuffer driver");
MODULE_LICENSE("GPL");