From e873c74132f0c5f1452816cd9bb26208f0bba1e1 Mon Sep 17 00:00:00 2001
From: Shivank Garg <shivankg@amd.com>
Date: Sat, 22 Aug 2026 19:22:05 +0000
Subject: dmaengine: fix use-after-free in dma_chan_put() and
 dma_release_channel()

When dma_device_put() drops the last reference on chan->device->ref,
dma_device_release() runs and may free the dma_device along with its
channels.

dma_chan_put() then still reads chan->device->owner via
dma_chan_to_owner() for the trailing module_put(). KASAN catches it:

	slab-use-after-free in dma_chan_put+0x3e6/0x4c0
	Read of size 8 by task insmod/6319
	Freed by task 6319:
	  kfree+0x225/0x470
	  dma_chan_put+0x395/0x4c0
	  dmaengine_put+0xf8/0x160

Cache the module owner in dma_chan_put() before the put so the trailing
module_put() does not need chan->device.

Fixes: 8ad342a86359 ("dmaengine: Add reference counting to dma_device struct")
Suggested-by: Sashiko <sashiko-bot@kernel.org>
Link: https://sashiko.dev/#/patchset/20260518-dmaengine-kref-fix-v1-1-4d6125048fb7@amd.com
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Shivank Garg <shivankg@amd.com>
Link: https://patch.msgid.link/20260822-dmaengine-kref-fix-v5-3-d4a4ee47d927@amd.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
---
 drivers/video/fbdev/udlfb.c | 2000 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 2000 insertions(+)
 create mode 100644 drivers/video/fbdev/udlfb.c

(limited to 'drivers/video/fbdev/udlfb.c')

diff --git a/drivers/video/fbdev/udlfb.c b/drivers/video/fbdev/udlfb.c
new file mode 100644
index 000000000..e78d6f95c
--- /dev/null
+++ b/drivers/video/fbdev/udlfb.c
@@ -0,0 +1,2000 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * 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>
+ *
+ * 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 <linux/slab.h>
+#include <linux/delay.h>
+#include <linux/unaligned.h>
+#include <video/udlfb.h>
+#include "edid.h"
+
+#define OUT_EP_NUM	1	/* The endpoint number we will use */
+
+static const 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_READS_FAST |
+		FBINFO_VIRTFB |
+		FBINFO_HWACCEL_IMAGEBLIT | FBINFO_HWACCEL_FILLRECT |
+		FBINFO_HWACCEL_COPYAREA | FBINFO_MISC_ALWAYS_SETPAR;
+
+/*
+ * There are many DisplayLink-based graphics products, all with unique PIDs.
+ * So we match on DisplayLink's VID + Vendor-Defined Interface Class (0xff)
+ * We also require a match on SubClass (0x00) and Protocol (0x00),
+ * which is compatible with all known USB 2.0 era graphics chips and firmware,
+ * but allows DisplayLink to increment those for any future incompatible chips
+ */
+static const struct usb_device_id id_table[] = {
+	{.idVendor = 0x17e9,
+	 .bInterfaceClass = 0xff,
+	 .bInterfaceSubClass = 0x00,
+	 .bInterfaceProtocol = 0x00,
+	 .match_flags = USB_DEVICE_ID_MATCH_VENDOR |
+		USB_DEVICE_ID_MATCH_INT_CLASS |
+		USB_DEVICE_ID_MATCH_INT_SUBCLASS |
+		USB_DEVICE_ID_MATCH_INT_PROTOCOL,
+	},
+	{},
+};
+MODULE_DEVICE_TABLE(usb, id_table);
+
+/* module options */
+static bool console = true; /* Allow fbcon to open framebuffer */
+static bool fb_defio = true;  /* Detect mmap writes using page faults */
+static bool shadow = true; /* Optionally disable shadow framebuffer */
+static int pixel_limit; /* Optionally force a pixel resolution limit */
+
+struct dlfb_deferred_free {
+	struct list_head list;
+	void *mem;
+};
+
+static int dlfb_realloc_framebuffer(struct dlfb_data *dlfb, struct fb_info *info, u32 new_len);
+
+/* 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 *dlfb);
+static int dlfb_submit_urb(struct dlfb_data *dlfb, struct urb * urb, size_t len);
+static int dlfb_alloc_urb_list(struct dlfb_data *dlfb, int count, size_t size);
+static void dlfb_free_urb_list(struct dlfb_data *dlfb);
+
+/*
+ * All DisplayLink bulk operations start with 0xAF, followed by specific code
+ * All operations are written to buffers which then later get sent to device
+ */
+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);
+}
+
+/*
+ * Map FB_BLANK_* to DisplayLink register
+ * DLReg FB_BLANK_*
+ * ----- -----------------------------
+ *  0x00 FB_BLANK_UNBLANK (0)
+ *  0x01 FB_BLANK (1)
+ *  0x03 FB_BLANK_VSYNC_SUSPEND (2)
+ *  0x05 FB_BLANK_HSYNC_SUSPEND (3)
+ *  0x07 FB_BLANK_POWERDOWN (4) Note: requires modeset to come back
+ */
+static char *dlfb_blanking(char *buf, int fb_blank)
+{
+	u8 reg;
+
+	switch (fb_blank) {
+	case FB_BLANK_POWERDOWN:
+		reg = 0x07;
+		break;
+	case FB_BLANK_HSYNC_SUSPEND:
+		reg = 0x05;
+		break;
+	case FB_BLANK_VSYNC_SUSPEND:
+		reg = 0x03;
+		break;
+	case FB_BLANK_NORMAL:
+		reg = 0x01;
+		break;
+	default:
+		reg = 0x00;
+	}
+
+	buf = dlfb_set_register(buf, 0x1F, reg);
+
+	return buf;
+}
+
+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);
+}
+
+/*
+ * DisplayLink HW has separate 16bpp and 8bpp framebuffers.
+ * In 24bpp modes, the low 323 RGB bits go in the 8bpp framebuffer
+ */
+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 dlfb_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, dlfb_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 *dlfb,
+				struct fb_var_screeninfo *var)
+{
+	char *buf;
+	char *wrptr;
+	int retval;
+	int writesize;
+	struct urb *urb;
+
+	if (!atomic_read(&dlfb->usb_active))
+		return -EPERM;
+
+	urb = dlfb_get_urb(dlfb);
+	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, dlfb->info->fix.smem_len);
+
+	wrptr = dlfb_set_vid_cmds(wrptr, var);
+	wrptr = dlfb_blanking(wrptr, FB_BLANK_UNBLANK);
+	wrptr = dlfb_vidreg_unlock(wrptr);
+
+	writesize = wrptr - buf;
+
+	retval = dlfb_submit_urb(dlfb, urb, writesize);
+
+	dlfb->blank_mode = FB_BLANK_UNBLANK;
+
+	return retval;
+}
+
+static void dlfb_vm_open(struct vm_area_struct *vma)
+{
+	struct dlfb_data *dlfb = vma->vm_private_data;
+
+	atomic_inc(&dlfb->mmap_count);
+}
+
+static void dlfb_vm_close(struct vm_area_struct *vma)
+{
+	struct dlfb_data *dlfb = vma->vm_private_data;
+
+	atomic_dec(&dlfb->mmap_count);
+}
+
+static const struct vm_operations_struct dlfb_vm_ops = {
+	.open  = dlfb_vm_open,
+	.close = dlfb_vm_close,
+};
+
+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;
+	struct dlfb_data *dlfb = info->par;
+
+	if (info->fbdefio)
+		return fb_deferred_io_mmap(info, vma);
+
+	vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
+
+	if (vma->vm_pgoff > (~0UL >> PAGE_SHIFT))
+		return -EINVAL;
+	if (size > info->fix.smem_len)
+		return -EINVAL;
+	if (offset > info->fix.smem_len - size)
+		return -EINVAL;
+
+	pos = (unsigned long)info->fix.smem_start + offset;
+
+	dev_dbg(info->dev, "mmap() framebuffer addr:%lu size:%lu\n",
+		pos, size);
+
+	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_ops = &dlfb_vm_ops;
+	vma->vm_private_data = dlfb;
+	atomic_inc(&dlfb->mmap_count);
+	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;
+	int start = width;
+	int end = width;
+
+	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,
+	unsigned long back_buffer_offset,
+	int *ident_ptr)
+{
+	const uint16_t *pixel = *pixel_start_ptr;
+	uint32_t dev_addr  = *device_address_ptr;
+	uint8_t *cmd = *command_buffer_ptr;
+
+	while ((pixel_end > pixel) &&
+	       (cmd_buffer_end - MIN_RLX_CMD_BYTES > cmd)) {
+		uint8_t *raw_pixels_count_byte = NULL;
+		uint8_t *cmd_pixels_count_byte = NULL;
+		const uint16_t *raw_pixel_start = NULL;
+		const uint16_t *cmd_pixel_start, *cmd_pixel_end = NULL;
+
+		if (back_buffer_offset &&
+		    *pixel == *(u16 *)((u8 *)pixel + back_buffer_offset)) {
+			pixel++;
+			dev_addr += BPP;
+			(*ident_ptr)++;
+			continue;
+		}
+
+		*cmd++ = 0xAF;
+		*cmd++ = 0x6B;
+		*cmd++ = dev_addr >> 16;
+		*cmd++ = dev_addr >> 8;
+		*cmd++ = dev_addr;
+
+		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 + min3(MAX_CMD_PIXELS + 1UL,
+					(unsigned long)(pixel_end - pixel),
+					(unsigned long)(cmd_buffer_end - 1 - cmd) / BPP);
+
+		if (back_buffer_offset) {
+			/* note: the framebuffer may change under us, so we must test for underflow */
+			while (cmd_pixel_end - 1 > pixel &&
+			       *(cmd_pixel_end - 1) == *(u16 *)((u8 *)(cmd_pixel_end - 1) + back_buffer_offset))
+				cmd_pixel_end--;
+		}
+
+		while (pixel < cmd_pixel_end) {
+			const uint16_t * const repeating_pixel = pixel;
+			u16 pixel_value = *pixel;
+
+			put_unaligned_be16(pixel_value, cmd);
+			if (back_buffer_offset)
+				*(u16 *)((u8 *)pixel + back_buffer_offset) = pixel_value;
+			cmd += 2;
+			pixel++;
+
+			if (unlikely((pixel < cmd_pixel_end) &&
+				     (*pixel == pixel_value))) {
+				/* go back and fill in raw pixel count */
+				*raw_pixels_count_byte = ((repeating_pixel -
+						raw_pixel_start) + 1) & 0xFF;
+
+				do {
+					if (back_buffer_offset)
+						*(u16 *)((u8 *)pixel + back_buffer_offset) = pixel_value;
+					pixel++;
+				} while ((pixel < cmd_pixel_end) &&
+					 (*pixel == pixel_value));
+
+				/* 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;
+		} else {
+			/* undo unused byte */
+			cmd--;
+		}
+
+		*cmd_pixels_count_byte = (pixel - cmd_pixel_start) & 0xFF;
+		dev_addr += (u8 *)pixel - (u8 *)cmd_pixel_start;
+	}
+
+	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;
+}
+
+/*
+ * 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 int dlfb_render_hline(struct dlfb_data *dlfb, 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 = dlfb->base16 + byte_offset;
+	struct urb *urb = *urb_ptr;
+	u8 *cmd = *urb_buf_ptr;
+	u8 *cmd_end = (u8 *) urb->transfer_buffer + urb->transfer_buffer_length;
+	unsigned long back_buffer_offset = 0;
+
+	line_start = (u8 *) (front + byte_offset);
+	next_pixel = line_start;
+	line_end = next_pixel + byte_width;
+
+	if (dlfb->backing_buffer) {
+		int offset;
+		const u8 *back_start = (u8 *) (dlfb->backing_buffer
+						+ byte_offset);
+
+		back_buffer_offset = (unsigned long)back_start - (unsigned long)line_start;
+
+		*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;
+	}
+
+	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, back_buffer_offset,
+			ident_ptr);
+
+		if (cmd >= cmd_end) {
+			int len = cmd - (u8 *) urb->transfer_buffer;
+			if (dlfb_submit_urb(dlfb, urb, len))
+				return 1; /* lost pixels is set */
+			*sent_ptr += len;
+			urb = dlfb_get_urb(dlfb);
+			if (!urb)
+				return 1; /* lost_pixels is set */
+			*urb_ptr = urb;
+			cmd = urb->transfer_buffer;
+			cmd_end = &cmd[urb->transfer_buffer_length];
+		}
+	}
+
+	*urb_buf_ptr = cmd;
+
+	return 0;
+}
+
+static int dlfb_handle_damage(struct dlfb_data *dlfb, int x, int y, int width, int height)
+{
+	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();
+
+	mutex_lock(&dlfb->render_mutex);
+
+	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 > dlfb->info->var.xres) ||
+	    (y + height > dlfb->info->var.yres)) {
+		ret = -EINVAL;
+		goto unlock_ret;
+	}
+
+	if (!atomic_read(&dlfb->usb_active)) {
+		ret = 0;
+		goto unlock_ret;
+	}
+
+	urb = dlfb_get_urb(dlfb);
+	if (!urb) {
+		ret = 0;
+		goto unlock_ret;
+	}
+	cmd = urb->transfer_buffer;
+
+	for (i = y; i < y + height ; i++) {
+		const int line_offset = dlfb->info->fix.line_length * i;
+		const int byte_offset = line_offset + (x * BPP);
+
+		if (dlfb_render_hline(dlfb, &urb,
+				      (char *) dlfb->info->fix.smem_start,
+				      &cmd, byte_offset, width * BPP,
+				      &bytes_identical, &bytes_sent))
+			goto error;
+	}
+
+	if (cmd > (char *) urb->transfer_buffer) {
+		int len;
+		if (cmd < (char *) urb->transfer_buffer + urb->transfer_buffer_length)
+			*cmd++ = 0xAF;
+		/* Send partial buffer remaining before exiting */
+		len = cmd - (char *) urb->transfer_buffer;
+		dlfb_submit_urb(dlfb, urb, len);
+		bytes_sent += len;
+	} else
+		dlfb_urb_completion(urb);
+
+error:
+	atomic_add(bytes_sent, &dlfb->bytes_sent);
+	atomic_add(bytes_identical, &dlfb->bytes_identical);
+	atomic_add(width*height*2, &dlfb->bytes_rendered);
+	end_cycles = get_cycles();
+	atomic_add(((unsigned int) ((end_cycles - start_cycles)
+		    >> 10)), /* Kcycles */
+		   &dlfb->cpu_kcycles_used);
+
+	ret = 0;
+
+unlock_ret:
+	mutex_unlock(&dlfb->render_mutex);
+	return ret;
+}
+
+static void dlfb_init_damage(struct dlfb_data *dlfb)
+{
+	dlfb->damage_x = INT_MAX;
+	dlfb->damage_x2 = 0;
+	dlfb->damage_y = INT_MAX;
+	dlfb->damage_y2 = 0;
+}
+
+static void dlfb_damage_work(struct work_struct *w)
+{
+	struct dlfb_data *dlfb = container_of(w, struct dlfb_data, damage_work);
+	int x, x2, y, y2;
+
+	spin_lock_irq(&dlfb->damage_lock);
+	x = dlfb->damage_x;
+	x2 = dlfb->damage_x2;
+	y = dlfb->damage_y;
+	y2 = dlfb->damage_y2;
+	dlfb_init_damage(dlfb);
+	spin_unlock_irq(&dlfb->damage_lock);
+
+	if (x < x2 && y < y2)
+		dlfb_handle_damage(dlfb, x, y, x2 - x, y2 - y);
+}
+
+static void dlfb_offload_damage(struct dlfb_data *dlfb, int x, int y, int width, int height)
+{
+	unsigned long flags;
+	int x2 = x + width;
+	int y2 = y + height;
+
+	if (x >= x2 || y >= y2)
+		return;
+
+	spin_lock_irqsave(&dlfb->damage_lock, flags);
+	dlfb->damage_x = min(x, dlfb->damage_x);
+	dlfb->damage_x2 = max(x2, dlfb->damage_x2);
+	dlfb->damage_y = min(y, dlfb->damage_y);
+	dlfb->damage_y2 = max(y2, dlfb->damage_y2);
+	spin_unlock_irqrestore(&dlfb->damage_lock, flags);
+
+	schedule_work(&dlfb->damage_work);
+}
+
+/*
+ * NOTE: fb_defio.c is holding info->fbdefio.mutex
+ *   Touching ANY framebuffer memory that triggers a page fault
+ *   in fb_defio will cause a deadlock, when it also tries to
+ *   grab the same mutex.
+ */
+static void dlfb_dpy_deferred_io(struct fb_info *info, struct list_head *pagereflist)
+{
+	struct fb_deferred_io_pageref *pageref;
+	struct dlfb_data *dlfb = 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;
+
+	mutex_lock(&dlfb->render_mutex);
+
+	if (!fb_defio)
+		goto unlock_ret;
+
+	if (!atomic_read(&dlfb->usb_active))
+		goto unlock_ret;
+
+	start_cycles = get_cycles();
+
+	urb = dlfb_get_urb(dlfb);
+	if (!urb)
+		goto unlock_ret;
+
+	cmd = urb->transfer_buffer;
+
+	/* walk the written page list and render each to device */
+	list_for_each_entry(pageref, pagereflist, list) {
+		if (dlfb_render_hline(dlfb, &urb, (char *) info->fix.smem_start,
+				      &cmd, pageref->offset, PAGE_SIZE,
+				      &bytes_identical, &bytes_sent))
+			goto error;
+		bytes_rendered += PAGE_SIZE;
+	}
+
+	if (cmd > (char *) urb->transfer_buffer) {
+		int len;
+		if (cmd < (char *) urb->transfer_buffer + urb->transfer_buffer_length)
+			*cmd++ = 0xAF;
+		/* Send partial buffer remaining before exiting */
+		len = cmd - (char *) urb->transfer_buffer;
+		dlfb_submit_urb(dlfb, urb, len);
+		bytes_sent += len;
+	} else
+		dlfb_urb_completion(urb);
+
+error:
+	atomic_add(bytes_sent, &dlfb->bytes_sent);
+	atomic_add(bytes_identical, &dlfb->bytes_identical);
+	atomic_add(bytes_rendered, &dlfb->bytes_rendered);
+	end_cycles = get_cycles();
+	atomic_add(((unsigned int) ((end_cycles - start_cycles)
+		    >> 10)), /* Kcycles */
+		   &dlfb->cpu_kcycles_used);
+unlock_ret:
+	mutex_unlock(&dlfb->render_mutex);
+}
+
+static int dlfb_get_edid(struct dlfb_data *dlfb, char *edid, int len)
+{
+	int i, ret;
+	char *rbuf;
+
+	rbuf = kmalloc(2, GFP_KERNEL);
+	if (!rbuf)
+		return 0;
+
+	for (i = 0; i < len; i++) {
+		ret = usb_control_msg(dlfb->udev,
+				      usb_rcvctrlpipe(dlfb->udev, 0), 0x02,
+				      (0x80 | (0x02 << 5)), i << 8, 0xA1,
+				      rbuf, 2, USB_CTRL_GET_TIMEOUT);
+		if (ret < 2) {
+			dev_err(&dlfb->udev->dev,
+				"Read EDID byte %d failed: %d\n", i, ret);
+			i--;
+			break;
+		}
+		edid[i] = rbuf[1];
+	}
+
+	kfree(rbuf);
+
+	return i;
+}
+
+static int dlfb_ops_ioctl(struct fb_info *info, unsigned int cmd,
+				unsigned long arg)
+{
+
+	struct dlfb_data *dlfb = info->par;
+
+	if (!atomic_read(&dlfb->usb_active))
+		return 0;
+
+	/* TODO: Update X server to get this from sysfs instead */
+	if (cmd == DLFB_IOCTL_RETURN_EDID) {
+		void __user *edid = (void __user *)arg;
+		if (copy_to_user(edid, dlfb->edid, dlfb->edid_size))
+			return -EFAULT;
+		return 0;
+	}
+
+	/* TODO: Help propose a standard fb.h ioctl to report mmap damage */
+	if (cmd == DLFB_IOCTL_REPORT_DAMAGE) {
+		struct dloarea area;
+
+		if (copy_from_user(&area, (void __user *)arg,
+				  sizeof(struct dloarea)))
+			return -EFAULT;
+
+		/*
+		 * If we have a damage-aware client, turn fb_defio "off"
+		 * To avoid perf imact of unnecessary page fault handling.
+		 * Done by resetting the delay for this fb_info to a very
+		 * long period. Pages will become writable and stay that way.
+		 * Reset to normal value when all clients have closed this fb.
+		 */
+		if (info->fbdefio)
+			info->fbdefio->delay = DL_DEFIO_WRITE_DISABLE;
+
+		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;
+
+		dlfb_handle_damage(dlfb, area.x, area.y, area.w, area.h);
+	}
+
+	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.
+ * Assumes caller is holding info->lock (for open and release at least)
+ */
+static int dlfb_ops_open(struct fb_info *info, int user)
+{
+	struct dlfb_data *dlfb = info->par;
+
+	/*
+	 * fbcon aggressively connects to first framebuffer it finds,
+	 * preventing other clients (X) from working properly. Usually
+	 * not what the user wants. Fail by default with option to enable.
+	 */
+	if ((user == 0) && (!console))
+		return -EBUSY;
+
+	/* If the USB device is gone, we don't accept new opens */
+	if (dlfb->virtualized)
+		return -ENODEV;
+
+	dlfb->fb_count++;
+
+	if (fb_defio && (info->fbdefio == NULL)) {
+		/* enable defio at last moment if not disabled by client */
+
+		struct fb_deferred_io *fbdefio;
+
+		fbdefio = kzalloc_obj(struct fb_deferred_io);
+
+		if (fbdefio) {
+			fbdefio->delay = DL_DEFIO_WRITE_DELAY;
+			fbdefio->sort_pagereflist = true;
+			fbdefio->deferred_io = dlfb_dpy_deferred_io;
+		}
+
+		info->fbdefio = fbdefio;
+		fb_deferred_io_init(info);
+	}
+
+	dev_dbg(info->dev, "open, user=%d fb_info=%p count=%d\n",
+		user, info, dlfb->fb_count);
+
+	return 0;
+}
+
+static void dlfb_ops_destroy(struct fb_info *info)
+{
+	struct dlfb_data *dlfb = info->par;
+
+	cancel_work_sync(&dlfb->damage_work);
+
+	mutex_destroy(&dlfb->render_mutex);
+
+	if (info->cmap.len != 0)
+		fb_dealloc_cmap(&info->cmap);
+	if (info->monspecs.modedb)
+		fb_destroy_modedb(info->monspecs.modedb);
+	vfree(info->screen_buffer);
+
+	fb_destroy_modelist(&info->modelist);
+
+	while (!list_empty(&dlfb->deferred_free)) {
+		struct dlfb_deferred_free *d = list_entry(dlfb->deferred_free.next, struct dlfb_deferred_free, list);
+		list_del(&d->list);
+		vfree(d->mem);
+		kfree(d);
+	}
+	vfree(dlfb->backing_buffer);
+	kfree(dlfb->edid);
+	dlfb_free_urb_list(dlfb);
+	usb_put_dev(dlfb->udev);
+	kfree(dlfb);
+
+	/* Assume info structure is freed after this point */
+	framebuffer_release(info);
+}
+
+/*
+ * Assumes caller is holding info->lock mutex (for open and release at least)
+ */
+static int dlfb_ops_release(struct fb_info *info, int user)
+{
+	struct dlfb_data *dlfb = info->par;
+
+	dlfb->fb_count--;
+
+	if ((dlfb->fb_count == 0) && (info->fbdefio)) {
+		fb_deferred_io_cleanup(info);
+		kfree(info->fbdefio);
+		info->fbdefio = NULL;
+	}
+
+	dev_dbg(info->dev, "release, user=%d count=%d\n", user, dlfb->fb_count);
+
+	return 0;
+}
+
+/*
+ * 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 dlfb_data *dlfb)
+{
+	if (mode->xres * mode->yres > dlfb->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;
+	struct dlfb_data *dlfb = info->par;
+
+	if (!var->pixclock)
+		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, dlfb))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int dlfb_ops_set_par(struct fb_info *info)
+{
+	struct dlfb_data *dlfb = info->par;
+	int result;
+	u16 *pix_framebuffer;
+	int i;
+	struct fb_var_screeninfo fvs;
+	u32 line_length = info->var.xres * (info->var.bits_per_pixel / 8);
+
+	/* clear the activate field because it causes spurious miscompares */
+	fvs = info->var;
+	fvs.activate = 0;
+	fvs.vmode &= ~FB_VMODE_SMOOTH_XPAN;
+
+	if (!memcmp(&dlfb->current_mode, &fvs, sizeof(struct fb_var_screeninfo)))
+		return 0;
+
+	result = dlfb_realloc_framebuffer(dlfb, info, info->var.yres * line_length);
+	if (result)
+		return result;
+
+	result = dlfb_set_video_mode(dlfb, &info->var);
+
+	if (result)
+		return result;
+
+	dlfb->current_mode = fvs;
+	info->fix.line_length = line_length;
+
+	if (dlfb->fb_count == 0) {
+
+		/* paint greenscreen */
+
+		pix_framebuffer = (u16 *)info->screen_buffer;
+		for (i = 0; i < info->fix.smem_len / 2; i++)
+			pix_framebuffer[i] = 0x37e6;
+	}
+
+	dlfb_handle_damage(dlfb, 0, 0, info->var.xres, info->var.yres);
+
+	return 0;
+}
+
+/* To fonzi the jukebox (e.g. make blanking changes take effect) */
+static char *dlfb_dummy_render(char *buf)
+{
+	*buf++ = 0xAF;
+	*buf++ = 0x6A; /* copy */
+	*buf++ = 0x00; /* from address*/
+	*buf++ = 0x00;
+	*buf++ = 0x00;
+	*buf++ = 0x01; /* one pixel */
+	*buf++ = 0x00; /* to address */
+	*buf++ = 0x00;
+	*buf++ = 0x00;
+	return buf;
+}
+
+/*
+ * In order to come back from full DPMS off, we need to set the mode again
+ */
+static int dlfb_ops_blank(int blank_mode, struct fb_info *info)
+{
+	struct dlfb_data *dlfb = info->par;
+	char *bufptr;
+	struct urb *urb;
+
+	dev_dbg(info->dev, "blank, mode %d --> %d\n",
+		dlfb->blank_mode, blank_mode);
+
+	if ((dlfb->blank_mode == FB_BLANK_POWERDOWN) &&
+	    (blank_mode != FB_BLANK_POWERDOWN)) {
+
+		/* returning from powerdown requires a fresh modeset */
+		dlfb_set_video_mode(dlfb, &info->var);
+	}
+
+	urb = dlfb_get_urb(dlfb);
+	if (!urb)
+		return 0;
+
+	bufptr = (char *) urb->transfer_buffer;
+	bufptr = dlfb_vidreg_lock(bufptr);
+	bufptr = dlfb_blanking(bufptr, blank_mode);
+	bufptr = dlfb_vidreg_unlock(bufptr);
+
+	/* seems like a render op is needed to have blank change take effect */
+	bufptr = dlfb_dummy_render(bufptr);
+
+	dlfb_submit_urb(dlfb, urb, bufptr -
+			(char *) urb->transfer_buffer);
+
+	dlfb->blank_mode = blank_mode;
+
+	return 0;
+}
+
+static void dlfb_ops_damage_range(struct fb_info *info, off_t off, size_t len)
+{
+	struct dlfb_data *dlfb = info->par;
+	int start = max((int)(off / info->fix.line_length), 0);
+	int lines = min((u32)((len / info->fix.line_length) + 1), (u32)info->var.yres);
+
+	dlfb_handle_damage(dlfb, 0, start, info->var.xres, lines);
+}
+
+static void dlfb_ops_damage_area(struct fb_info *info, u32 x, u32 y, u32 width, u32 height)
+{
+	struct dlfb_data *dlfb = info->par;
+
+	dlfb_offload_damage(dlfb, x, y, width, height);
+}
+
+FB_GEN_DEFAULT_DEFERRED_SYSMEM_OPS(dlfb_ops,
+				   dlfb_ops_damage_range,
+				   dlfb_ops_damage_area)
+
+static const struct fb_ops dlfb_ops = {
+	.owner = THIS_MODULE,
+	__FB_DEFAULT_DEFERRED_OPS_RDWR(dlfb_ops),
+	.fb_setcolreg = dlfb_ops_setcolreg,
+	__FB_DEFAULT_DEFERRED_OPS_DRAW(dlfb_ops),
+	.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,
+	.fb_destroy = dlfb_ops_destroy,
+};
+
+
+static void dlfb_deferred_vfree(struct dlfb_data *dlfb, void *mem)
+{
+	struct dlfb_deferred_free *d = kmalloc_obj(struct dlfb_deferred_free);
+	if (!d)
+		return;
+	d->mem = mem;
+	list_add(&d->list, &dlfb->deferred_free);
+}
+
+/*
+ * Assumes &info->lock held by caller
+ */
+static int dlfb_realloc_framebuffer(struct dlfb_data *dlfb, struct fb_info *info, u32 new_len)
+{
+	u32 old_len = info->fix.smem_len;
+	const void *old_fb = info->screen_buffer;
+	unsigned char *new_fb;
+	unsigned char *new_back = NULL;
+
+	new_len = PAGE_ALIGN(new_len);
+
+	if (new_len > old_len) {
+		if (atomic_read(&dlfb->mmap_count) > 0) {
+			dev_warn(info->dev,
+				"refusing realloc: %d active mmaps\n",
+				atomic_read(&dlfb->mmap_count));
+			return -EBUSY;
+		}
+
+		/*
+		 * Alloc system memory for virtual framebuffer
+		 */
+		new_fb = vmalloc(new_len);
+		if (!new_fb) {
+			dev_err(info->dev, "Virtual framebuffer alloc failed\n");
+			return -ENOMEM;
+		}
+		memset(new_fb, 0xff, new_len);
+
+		if (info->screen_buffer) {
+			memcpy(new_fb, old_fb, old_len);
+			dlfb_deferred_vfree(dlfb, info->screen_buffer);
+		}
+
+		info->screen_buffer = new_fb;
+		info->fix.smem_len = new_len;
+		info->fix.smem_start = (unsigned long) new_fb;
+		info->flags = udlfb_info_flags;
+
+		/*
+		 * Second framebuffer copy to mirror the framebuffer state
+		 * on the physical USB device. We can function without this.
+		 * But with imperfect damage info we may send pixels over USB
+		 * that were, in fact, unchanged - wasting limited USB bandwidth
+		 */
+		if (shadow)
+			new_back = vzalloc(new_len);
+		if (!new_back)
+			dev_info(info->dev,
+				 "No shadow/backing buffer allocated\n");
+		else {
+			dlfb_deferred_vfree(dlfb, dlfb->backing_buffer);
+			dlfb->backing_buffer = new_back;
+		}
+	}
+	return 0;
+}
+
+/*
+ * 1) Get EDID from hw, or use sw default
+ * 2) Parse into various fb_info structs
+ * 3) Allocate virtual framebuffer memory to back highest res mode
+ *
+ * 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 successful
+ */
+static int dlfb_setup_modes(struct dlfb_data *dlfb,
+			   struct fb_info *info,
+			   char *default_edid, size_t default_edid_size)
+{
+	char *edid;
+	int i, result = 0, tries = 3;
+	struct device *dev = info->device;
+	struct fb_videomode *mode;
+	const struct fb_videomode *default_vmode = NULL;
+
+	if (info->dev) {
+		/* only use mutex if info has been registered */
+		mutex_lock(&info->lock);
+		/* parent device is used otherwise */
+		dev = info->dev;
+	}
+
+	edid = kmalloc(EDID_LENGTH, GFP_KERNEL);
+	if (!edid) {
+		result = -ENOMEM;
+		goto error;
+	}
+
+	fb_destroy_modelist(&info->modelist);
+	memset(&info->monspecs, 0, sizeof(info->monspecs));
+
+	/*
+	 * Try to (re)read EDID from hardware first
+	 * EDID data may return, but not parse as valid
+	 * Try again a few times, in case of e.g. analog cable noise
+	 */
+	while (tries--) {
+
+		i = dlfb_get_edid(dlfb, edid, EDID_LENGTH);
+
+		if (i >= EDID_LENGTH)
+			fb_edid_to_monspecs(edid, &info->monspecs);
+
+		if (info->monspecs.modedb_len > 0) {
+			dlfb->edid = edid;
+			dlfb->edid_size = i;
+			break;
+		}
+	}
+
+	/* If that fails, use a previously returned EDID if available */
+	if (info->monspecs.modedb_len == 0) {
+		dev_err(dev, "Unable to get valid EDID from device/display\n");
+
+		if (dlfb->edid) {
+			fb_edid_to_monspecs(dlfb->edid, &info->monspecs);
+			if (info->monspecs.modedb_len > 0)
+				dev_err(dev, "Using previously queried EDID\n");
+		}
+	}
+
+	/* If that fails, use the default EDID we were handed */
+	if (info->monspecs.modedb_len == 0) {
+		if (default_edid_size >= EDID_LENGTH) {
+			fb_edid_to_monspecs(default_edid, &info->monspecs);
+			if (info->monspecs.modedb_len > 0) {
+				memcpy(edid, default_edid, default_edid_size);
+				dlfb->edid = edid;
+				dlfb->edid_size = default_edid_size;
+				dev_err(dev, "Using default/backup EDID\n");
+			}
+		}
+	}
+
+	/* If we've got modes, let's pick a best default mode */
+	if (info->monspecs.modedb_len > 0) {
+
+		for (i = 0; i < info->monspecs.modedb_len; i++) {
+			mode = &info->monspecs.modedb[i];
+			if (dlfb_is_valid_mode(mode, dlfb)) {
+				fb_add_videomode(mode, &info->modelist);
+			} else {
+				dev_dbg(dev, "Specified mode %dx%d too big\n",
+					mode->xres, mode->yres);
+				if (i == 0)
+					/* if we've removed top/best mode */
+					info->monspecs.misc
+						&= ~FB_MISC_1ST_DETAIL;
+			}
+		}
+
+		default_vmode = fb_find_best_display(&info->monspecs,
+						     &info->modelist);
+	}
+
+	/* If everything else has failed, fall back to safe default mode */
+	if (default_vmode == NULL) {
+
+		struct fb_videomode fb_vmode = {0};
+
+		/*
+		 * 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++) {
+			mode = (struct fb_videomode *)&vesa_modes[i];
+			if (dlfb_is_valid_mode(mode, dlfb))
+				fb_add_videomode(mode, &info->modelist);
+			else
+				dev_dbg(dev, "VESA mode %dx%d too big\n",
+					mode->xres, mode->yres);
+		}
+
+		/*
+		 * 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);
+	}
+
+	/* If we have good mode and no active clients*/
+	if ((default_vmode != NULL) && (dlfb->fb_count == 0)) {
+
+		fb_videomode_to_var(&info->var, default_vmode);
+		dlfb_var_color_format(&info->var);
+
+		/*
+		 * with mode size info, we can now alloc our framebuffer.
+		 */
+		memcpy(&info->fix, &dlfb_fix, sizeof(dlfb_fix));
+	} else
+		result = -EINVAL;
+
+error:
+	if (edid && (dlfb->edid != edid))
+		kfree(edid);
+
+	if (info->dev)
+		mutex_unlock(&info->lock);
+
+	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 *dlfb = fb_info->par;
+	return sysfs_emit(buf, "%u\n",
+			atomic_read(&dlfb->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 *dlfb = fb_info->par;
+	return sysfs_emit(buf, "%u\n",
+			atomic_read(&dlfb->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 *dlfb = fb_info->par;
+	return sysfs_emit(buf, "%u\n",
+			atomic_read(&dlfb->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 *dlfb = fb_info->par;
+	return sysfs_emit(buf, "%u\n",
+			atomic_read(&dlfb->cpu_kcycles_used));
+}
+
+static ssize_t edid_show(
+			struct file *filp,
+			struct kobject *kobj, const struct bin_attribute *a,
+			 char *buf, loff_t off, size_t count) {
+	struct device *fbdev = kobj_to_dev(kobj);
+	struct fb_info *fb_info = dev_get_drvdata(fbdev);
+	struct dlfb_data *dlfb = fb_info->par;
+
+	if (dlfb->edid == NULL)
+		return 0;
+
+	if ((off >= dlfb->edid_size) || (count > dlfb->edid_size))
+		return 0;
+
+	if (off + count > dlfb->edid_size)
+		count = dlfb->edid_size - off;
+
+	memcpy(buf, dlfb->edid, count);
+
+	return count;
+}
+
+static ssize_t edid_store(
+			struct file *filp,
+			struct kobject *kobj, const struct bin_attribute *a,
+			char *src, loff_t src_off, size_t src_size) {
+	struct device *fbdev = kobj_to_dev(kobj);
+	struct fb_info *fb_info = dev_get_drvdata(fbdev);
+	struct dlfb_data *dlfb = fb_info->par;
+	int ret;
+
+	/* We only support write of entire EDID at once, no offset*/
+	if ((src_size != EDID_LENGTH) || (src_off != 0))
+		return -EINVAL;
+
+	ret = dlfb_setup_modes(dlfb, fb_info, src, src_size);
+	if (ret)
+		return ret;
+
+	if (!dlfb->edid || memcmp(src, dlfb->edid, src_size))
+		return -EINVAL;
+
+	ret = dlfb_ops_set_par(fb_info);
+	if (ret)
+		return ret;
+
+	return src_size;
+}
+
+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 *dlfb = fb_info->par;
+
+	atomic_set(&dlfb->bytes_rendered, 0);
+	atomic_set(&dlfb->bytes_identical, 0);
+	atomic_set(&dlfb->bytes_sent, 0);
+	atomic_set(&dlfb->cpu_kcycles_used, 0);
+
+	return count;
+}
+
+static const struct bin_attribute edid_attr = {
+	.attr.name = "edid",
+	.attr.mode = 0666,
+	.size = EDID_LENGTH,
+	.read = edid_show,
+	.write = edid_store
+};
+
+static const 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(metrics_reset, S_IWUSR, NULL, metrics_reset_store),
+};
+
+/*
+ * This is necessary before we can communicate with the display controller.
+ */
+static int dlfb_select_std_channel(struct dlfb_data *dlfb)
+{
+	int ret;
+	static const u8 set_def_chn[] = {
+				0x57, 0xCD, 0xDC, 0xA7,
+				0x1C, 0x88, 0x5E, 0x15,
+				0x60, 0xFE, 0xC6, 0x97,
+				0x16, 0x3D, 0x47, 0xF2  };
+
+	ret = usb_control_msg_send(dlfb->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,
+			GFP_KERNEL);
+
+	return ret;
+}
+
+static int dlfb_parse_vendor_descriptor(struct dlfb_data *dlfb,
+					struct usb_interface *intf)
+{
+	char *desc;
+	char *buf;
+	char *desc_end;
+	int total_len;
+
+	buf = kzalloc(MAX_VENDOR_DESCRIPTOR_SIZE, GFP_KERNEL);
+	if (!buf)
+		return false;
+	desc = buf;
+
+	total_len = usb_get_descriptor(interface_to_usbdev(intf),
+					0x5f, /* vendor specific */
+					0, desc, MAX_VENDOR_DESCRIPTOR_SIZE);
+
+	/* if not found, look in configuration descriptor */
+	if (total_len < 0) {
+		if (0 == usb_get_extra_descriptor(intf->cur_altsetting,
+			0x5f, &desc))
+			total_len = (int) desc[0];
+	}
+
+	if (total_len > 5) {
+		dev_info(&intf->dev,
+			 "vendor descriptor length: %d data: %11ph\n",
+			 total_len, desc);
+
+		if ((desc[0] != total_len) || /* descriptor length */
+		    (desc[1] != 0x5f) ||   /* vendor descriptor type */
+		    (desc[2] != 0x01) ||   /* version (2 bytes) */
+		    (desc[3] != 0x00) ||
+		    (desc[4] != total_len - 2)) /* length after type */
+			goto unrecognized;
+
+		desc_end = desc + total_len;
+		desc += 5; /* the fixed header we've already parsed */
+
+		while (desc < desc_end) {
+			char *value;
+			u8 length;
+			u16 key;
+
+			if (desc_end - desc < sizeof(key) + sizeof(length))
+				goto unrecognized;
+
+			key = get_unaligned_le16(desc);
+			desc += sizeof(key);
+			length = *desc++;
+
+			if (length > desc_end - desc)
+				goto unrecognized;
+
+			value = desc;
+			switch (key) {
+			case 0x0200: { /* max_area */
+				u32 max_area;
+
+				if (length < sizeof(max_area))
+					goto unrecognized;
+
+				max_area = get_unaligned_le32(value);
+				dev_warn(&intf->dev,
+					 "DL chip limited to %d pixel modes\n",
+					 max_area);
+				dlfb->sku_pixel_limit = max_area;
+				break;
+			}
+			default:
+				break;
+			}
+			desc += length;
+		}
+	} else {
+		dev_info(&intf->dev, "vendor descriptor not available (%d)\n",
+			 total_len);
+	}
+
+	goto success;
+
+unrecognized:
+	/* allow udlfb to load for now even if firmware unrecognized */
+	dev_err(&intf->dev, "Unrecognized vendor firmware descriptor\n");
+
+success:
+	kfree(buf);
+	return true;
+}
+
+static int dlfb_usb_probe(struct usb_interface *intf,
+			  const struct usb_device_id *id)
+{
+	int i;
+	const struct device_attribute *attr;
+	struct dlfb_data *dlfb;
+	struct fb_info *info;
+	int retval;
+	struct usb_device *usbdev = interface_to_usbdev(intf);
+	static u8 out_ep[] = {OUT_EP_NUM + USB_DIR_OUT, 0};
+
+	/* usb initialization */
+	dlfb = kzalloc_obj(*dlfb);
+	if (!dlfb) {
+		dev_err(&intf->dev, "%s: failed to allocate dlfb\n", __func__);
+		return -ENOMEM;
+	}
+
+	INIT_LIST_HEAD(&dlfb->deferred_free);
+
+	dlfb->udev = usb_get_dev(usbdev);
+	usb_set_intfdata(intf, dlfb);
+
+	if (!usb_check_bulk_endpoints(intf, out_ep)) {
+		dev_err(&intf->dev, "Invalid DisplayLink device!\n");
+		retval = -EINVAL;
+		goto error;
+	}
+
+	dev_dbg(&intf->dev, "console enable=%d\n", console);
+	dev_dbg(&intf->dev, "fb_defio enable=%d\n", fb_defio);
+	dev_dbg(&intf->dev, "shadow enable=%d\n", shadow);
+
+	dlfb->sku_pixel_limit = 2048 * 1152; /* default to maximum */
+
+	if (!dlfb_parse_vendor_descriptor(dlfb, intf)) {
+		dev_err(&intf->dev,
+			"firmware not recognized, incompatible device?\n");
+		retval = -ENODEV;
+		goto error;
+	}
+
+	if (pixel_limit) {
+		dev_warn(&intf->dev,
+			 "DL chip limit of %d overridden to %d\n",
+			 dlfb->sku_pixel_limit, pixel_limit);
+		dlfb->sku_pixel_limit = pixel_limit;
+	}
+
+
+	/* allocates framebuffer driver structure, not framebuffer memory */
+	info = framebuffer_alloc(0, &dlfb->udev->dev);
+	if (!info) {
+		retval = -ENOMEM;
+		goto error;
+	}
+
+	dlfb->info = info;
+	info->par = dlfb;
+	info->pseudo_palette = dlfb->pseudo_palette;
+	dlfb->ops = dlfb_ops;
+	info->fbops = &dlfb->ops;
+
+	mutex_init(&dlfb->render_mutex);
+	dlfb_init_damage(dlfb);
+	spin_lock_init(&dlfb->damage_lock);
+	INIT_WORK(&dlfb->damage_work, dlfb_damage_work);
+
+	INIT_LIST_HEAD(&info->modelist);
+
+	if (!dlfb_alloc_urb_list(dlfb, WRITES_IN_FLIGHT, MAX_TRANSFER)) {
+		retval = -ENOMEM;
+		dev_err(&intf->dev, "unable to allocate urb list\n");
+		goto error;
+	}
+
+	/* We don't register a new USB class. Our client interface is dlfbev */
+
+	retval = fb_alloc_cmap(&info->cmap, 256, 0);
+	if (retval < 0) {
+		dev_err(info->device, "cmap allocation failed: %d\n", retval);
+		goto error;
+	}
+
+	retval = dlfb_setup_modes(dlfb, info, NULL, 0);
+	if (retval != 0) {
+		dev_err(info->device,
+			"unable to find common mode for display and adapter\n");
+		goto error;
+	}
+
+	/* ready to begin using device */
+
+	atomic_set(&dlfb->usb_active, 1);
+	dlfb_select_std_channel(dlfb);
+
+	dlfb_ops_check_var(&info->var, info);
+	retval = dlfb_ops_set_par(info);
+	if (retval)
+		goto error;
+
+	retval = register_framebuffer(info);
+	if (retval < 0) {
+		dev_err(info->device, "unable to register framebuffer: %d\n",
+			retval);
+		goto error;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(fb_device_attrs); i++) {
+		attr = &fb_device_attrs[i];
+		retval = device_create_file(info->dev, attr);
+		if (retval)
+			dev_warn(info->device,
+				 "failed to create '%s' attribute: %d\n",
+				 attr->attr.name, retval);
+	}
+
+	retval = device_create_bin_file(info->dev, &edid_attr);
+	if (retval)
+		dev_warn(info->device, "failed to create '%s' attribute: %d\n",
+			 edid_attr.attr.name, retval);
+
+	dev_info(info->device,
+		 "%s is DisplayLink USB device (%dx%d, %dK framebuffer memory)\n",
+		 dev_name(info->dev), info->var.xres, info->var.yres,
+		 ((dlfb->backing_buffer) ?
+		 info->fix.smem_len * 2 : info->fix.smem_len) >> 10);
+	return 0;
+
+error:
+	if (dlfb->info) {
+		dlfb_ops_destroy(dlfb->info);
+	} else {
+		usb_put_dev(dlfb->udev);
+		kfree(dlfb);
+	}
+	return retval;
+}
+
+static void dlfb_usb_disconnect(struct usb_interface *intf)
+{
+	struct dlfb_data *dlfb;
+	struct fb_info *info;
+	int i;
+
+	dlfb = usb_get_intfdata(intf);
+	info = dlfb->info;
+
+	dev_dbg(&intf->dev, "USB disconnect starting\n");
+
+	/* we virtualize until all fb clients release. Then we free */
+	dlfb->virtualized = true;
+
+	/* When non-active we'll update virtual framebuffer, but no new urbs */
+	atomic_set(&dlfb->usb_active, 0);
+
+	/* this function will wait for all in-flight urbs to complete */
+	dlfb_free_urb_list(dlfb);
+
+	/* remove udlfb's sysfs interfaces */
+	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);
+
+	unregister_framebuffer(info);
+}
+
+static struct usb_driver dlfb_driver = {
+	.name = "udlfb",
+	.probe = dlfb_usb_probe,
+	.disconnect = dlfb_usb_disconnect,
+	.id_table = id_table,
+};
+
+module_usb_driver(dlfb_driver);
+
+static void dlfb_urb_completion(struct urb *urb)
+{
+	struct urb_node *unode = urb->context;
+	struct dlfb_data *dlfb = unode->dlfb;
+	unsigned long flags;
+
+	switch (urb->status) {
+	case 0:
+		/* success */
+		break;
+	case -ECONNRESET:
+	case -ENOENT:
+	case -ESHUTDOWN:
+		/* sync/async unlink faults aren't errors */
+		break;
+	default:
+		dev_err(&dlfb->udev->dev,
+			"%s - nonzero write bulk status received: %d\n",
+			__func__, urb->status);
+		atomic_set(&dlfb->lost_pixels, 1);
+		break;
+	}
+
+	urb->transfer_buffer_length = dlfb->urbs.size; /* reset to actual */
+
+	spin_lock_irqsave(&dlfb->urbs.lock, flags);
+	list_add_tail(&unode->entry, &dlfb->urbs.list);
+	dlfb->urbs.available++;
+	spin_unlock_irqrestore(&dlfb->urbs.lock, flags);
+
+	up(&dlfb->urbs.limit_sem);
+}
+
+static void dlfb_free_urb_list(struct dlfb_data *dlfb)
+{
+	int count = dlfb->urbs.count;
+	struct list_head *node;
+	struct urb_node *unode;
+	struct urb *urb;
+
+	/* keep waiting and freeing, until we've got 'em all */
+	while (count--) {
+		down(&dlfb->urbs.limit_sem);
+
+		spin_lock_irq(&dlfb->urbs.lock);
+
+		node = dlfb->urbs.list.next; /* have reserved one with sem */
+		list_del_init(node);
+
+		spin_unlock_irq(&dlfb->urbs.lock);
+
+		unode = list_entry(node, struct urb_node, entry);
+		urb = unode->urb;
+
+		/* Free each separately allocated piece */
+		usb_free_coherent(urb->dev, dlfb->urbs.size,
+				  urb->transfer_buffer, urb->transfer_dma);
+		usb_free_urb(urb);
+		kfree(node);
+	}
+
+	dlfb->urbs.count = 0;
+}
+
+static int dlfb_alloc_urb_list(struct dlfb_data *dlfb, int count, size_t size)
+{
+	struct urb *urb;
+	struct urb_node *unode;
+	char *buf;
+	size_t wanted_size = count * size;
+
+	spin_lock_init(&dlfb->urbs.lock);
+
+retry:
+	dlfb->urbs.size = size;
+	INIT_LIST_HEAD(&dlfb->urbs.list);
+
+	sema_init(&dlfb->urbs.limit_sem, 0);
+	dlfb->urbs.count = 0;
+	dlfb->urbs.available = 0;
+
+	while (dlfb->urbs.count * size < wanted_size) {
+		unode = kzalloc_obj(*unode);
+		if (!unode)
+			break;
+		unode->dlfb = dlfb;
+
+		urb = usb_alloc_urb(0, GFP_KERNEL);
+		if (!urb) {
+			kfree(unode);
+			break;
+		}
+		unode->urb = urb;
+
+		buf = usb_alloc_coherent(dlfb->udev, size, GFP_KERNEL,
+					 &urb->transfer_dma);
+		if (!buf) {
+			kfree(unode);
+			usb_free_urb(urb);
+			if (size > PAGE_SIZE) {
+				size /= 2;
+				dlfb_free_urb_list(dlfb);
+				goto retry;
+			}
+			break;
+		}
+
+		/* urb->transfer_buffer_length set to actual before submit */
+		usb_fill_bulk_urb(urb, dlfb->udev,
+			usb_sndbulkpipe(dlfb->udev, OUT_EP_NUM),
+			buf, size, dlfb_urb_completion, unode);
+		urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
+
+		list_add_tail(&unode->entry, &dlfb->urbs.list);
+
+		up(&dlfb->urbs.limit_sem);
+		dlfb->urbs.count++;
+		dlfb->urbs.available++;
+	}
+
+	return dlfb->urbs.count;
+}
+
+static struct urb *dlfb_get_urb(struct dlfb_data *dlfb)
+{
+	int ret;
+	struct list_head *entry;
+	struct urb_node *unode;
+
+	/* Wait for an in-flight buffer to complete and get re-queued */
+	ret = down_timeout(&dlfb->urbs.limit_sem, GET_URB_TIMEOUT);
+	if (ret) {
+		atomic_set(&dlfb->lost_pixels, 1);
+		dev_warn(&dlfb->udev->dev,
+			 "wait for urb interrupted: %d available: %d\n",
+			 ret, dlfb->urbs.available);
+		return NULL;
+	}
+
+	spin_lock_irq(&dlfb->urbs.lock);
+
+	BUG_ON(list_empty(&dlfb->urbs.list)); /* reserved one with limit_sem */
+	entry = dlfb->urbs.list.next;
+	list_del_init(entry);
+	dlfb->urbs.available--;
+
+	spin_unlock_irq(&dlfb->urbs.lock);
+
+	unode = list_entry(entry, struct urb_node, entry);
+	return unode->urb;
+}
+
+static int dlfb_submit_urb(struct dlfb_data *dlfb, struct urb *urb, size_t len)
+{
+	int ret;
+
+	BUG_ON(len > dlfb->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(&dlfb->lost_pixels, 1);
+		dev_err(&dlfb->udev->dev, "submit urb error: %d\n", ret);
+	}
+	return ret;
+}
+
+module_param(console, bool, S_IWUSR | S_IRUSR | S_IWGRP | S_IRGRP);
+MODULE_PARM_DESC(console, "Allow fbcon to open framebuffer");
+
+module_param(fb_defio, bool, S_IWUSR | S_IRUSR | S_IWGRP | S_IRGRP);
+MODULE_PARM_DESC(fb_defio, "Page fault detection of mmap writes");
+
+module_param(shadow, bool, S_IWUSR | S_IRUSR | S_IWGRP | S_IRGRP);
+MODULE_PARM_DESC(shadow, "Shadow vid mem. Disable to save mem but lose perf");
+
+module_param(pixel_limit, int, S_IWUSR | S_IRUSR | S_IWGRP | S_IRGRP);
+MODULE_PARM_DESC(pixel_limit, "Force limit on max mode (in x*y pixels)");
+
+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");
+
-- 
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