/*
 * 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.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#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/prefetch.h>
#include <linux/delay.h>
#include <video/udlfb.h>
#include "edid.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 |
                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 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 = 1; /* Allow fbcon to open framebuffer */
static bool fb_defio = 1;  /* Detect mmap writes using page faults */
static bool shadow = 1; /* Optionally disable shadow framebuffer */
static int pixel_limit; /* Optionally force a pixel resolution limit */

/* 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);

/*
 * 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 *dev,
                                struct fb_var_screeninfo *var)
{
        char *buf;
        char *wrptr;
        int retval;
        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_blanking(wrptr, FB_BLANK_UNBLANK);
        wrptr = dlfb_vidreg_unlock(wrptr);

        writesize = wrptr - buf;

        retval = dlfb_submit_urb(dev, urb, writesize);

        dev->blank_mode = FB_BLANK_UNBLANK;

        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;

        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;

        pr_notice("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;
        }

        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 = 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;

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

                *cmd++ = 0xAF;
                *cmd++ = 0x6B;
                *cmd++ = (uint8_t) ((dev_addr >> 16) & 0xFF);
                *cmd++ = (uint8_t) ((dev_addr >> 8) & 0xFF);
                *cmd++ = (uint8_t) ((dev_addr) & 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 int 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 1; /* lost pixels is set */
                        *sent_ptr += len;
                        urb = dlfb_get_urb(dev);
                        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 *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);

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

        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);

error:
        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;
}

/*
 * Path triggered by usermode clients who write to filesystem
 * e.g. cat filename > /dev/fb1
 * Not used by X Windows or text-mode console. But useful for testing.
 * Slow because of extra copy and we must assume all pixels dirty.
 */
static ssize_t dlfb_ops_write(struct fb_info *info, const char __user *buf,
                          size_t count, loff_t *ppos)
{
        ssize_t result;
        struct dlfb_data *dev = info->par;
        u32 offset = (u32) *ppos;

        result = fb_sys_write(info, buf, count, ppos);

        if (result > 0) {
                int start = max((int)(offset / info->fix.line_length), 0);
                int lines = min((u32)((result / info->fix.line_length) + 1),
                                (u32)info->var.yres);

                dlfb_handle_damage(dev, 0, start, info->var.xres,
                        lines, info->screen_base);
        }

        return result;
}

/* 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;

        sys_copyarea(info, area);

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

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

        sys_imageblit(info, image);

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

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

        sys_fillrect(info, rect);

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

/*
 * 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 *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;

        if (!fb_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) {

                if (dlfb_render_hline(dev, &urb, (char *) info->fix.smem_start,
                                  &cmd, cur->index << PAGE_SHIFT,
                                  PAGE_SIZE, &bytes_identical, &bytes_sent))
                        goto error;
                bytes_rendered += PAGE_SIZE;
        }

        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);

error:
        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 int dlfb_get_edid(struct dlfb_data *dev, char *edid, int len)
{
        int i;
        int ret;
        char *rbuf;

        rbuf = kmalloc(2, GFP_KERNEL);
        if (!rbuf)
                return 0;

        for (i = 0; i < len; i++) {
                ret = usb_control_msg(dev->udev,
                                    usb_rcvctrlpipe(dev->udev, 0), (0x02),
                                    (0x80 | (0x02 << 5)), i << 8, 0xA1, rbuf, 2,
                                    HZ);
                if (ret < 1) {
                        pr_err("Read EDID byte %d failed err %x\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 *dev = info->par;

        if (!atomic_read(&dev->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, dev->edid, dev->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(dev, area.x, area.y, area.w, area.h,
                           info->screen_base);
        }

        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 *dev = 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 (dev->virtualized)
                return -ENODEV;

        dev->fb_count++;

        kref_get(&dev->kref);

        if (fb_defio && (info->fbdefio == NULL)) {
                /* enable defio at last moment if not disabled by client */

                struct fb_deferred_io *fbdefio;

                fbdefio = kzalloc(sizeof(struct fb_deferred_io), GFP_KERNEL);

                if (fbdefio) {
                        fbdefio->delay = DL_DEFIO_WRITE_DELAY;
                        fbdefio->deferred_io = dlfb_dpy_deferred_io;
                }

                info->fbdefio = fbdefio;
                fb_deferred_io_init(info);
        }

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

        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_free(struct kref *kref)
{
        struct dlfb_data *dev = container_of(kref, struct dlfb_data, kref);

        vfree(dev->backing_buffer);

        kfree(dev->edid);

        pr_warn("freeing dlfb_data %p\n", dev);

        kfree(dev);
}

static void dlfb_release_urb_work(struct work_struct *work)
{
        struct urb_node *unode = container_of(work, struct urb_node,
                                              release_urb_work.work);

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

static void dlfb_free_framebuffer(struct dlfb_data *dev)
{
        struct fb_info *info = dev->info;

        if (info) {
                int node = info->node;

                unregister_framebuffer(info);

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

                fb_destroy_modelist(&info->modelist);

                dev->info = NULL;

                /* Assume info structure is freed after this point */
                framebuffer_release(info);

                pr_warn("fb_info for /dev/fb%d has been freed\n", node);
        }

        /* ref taken in probe() as part of registering framebfufer */
        kref_put(&dev->kref, dlfb_free);
}

static void dlfb_free_framebuffer_work(struct work_struct *work)
{
        struct dlfb_data *dev = container_of(work, struct dlfb_data,
                                             free_framebuffer_work.work);
        dlfb_free_framebuffer(dev);
}
/*
 * 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 *dev = info->par;

        dev->fb_count--;

        /* We can't free fb_info here - fbmem will touch it when we return */
        if (dev->virtualized && (dev->fb_count == 0))
                schedule_delayed_work(&dev->free_framebuffer_work, HZ);

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

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

        kref_put(&dev->kref, dlfb_free);

        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 fb_info *info)
{
        struct dlfb_data *dev = info->par;

        if (mode->xres * mode->yres > dev->sku_pixel_limit) {
                pr_warn("%dx%d beyond chip capabilities\n",
                       mode->xres, mode->yres);
                return 0;
        }

        pr_info("%dx%d @ %d Hz valid mode\n", mode->xres, mode->yres,
                mode->refresh);

        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;
        int result;
        u16 *pix_framebuffer;
        int i;

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

        result = dlfb_set_video_mode(dev, &info->var);

        if ((result == 0) && (dev->fb_count == 0)) {

                /* paint greenscreen */

                pix_framebuffer = (u16 *) info->screen_base;
                for (i = 0; i < info->fix.smem_len / 2; i++)
                        pix_framebuffer[i] = 0x37e6;

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

        return result;
}

/* 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 *dev = info->par;
        char *bufptr;
        struct urb *urb;

        pr_debug("/dev/fb%d FB_BLANK mode %d --> %d\n",
                 info->node, dev->blank_mode, blank_mode);

        if ((dev->blank_mode == FB_BLANK_POWERDOWN) &&
            (blank_mode != FB_BLANK_POWERDOWN)) {

                /* returning from powerdown requires a fresh modeset */
                dlfb_set_video_mode(dev, &info->var);
        }

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

        dev->blank_mode = blank_mode;

        return 0;
}

static struct fb_ops dlfb_ops = {
        .owner = THIS_MODULE,
        .fb_read = fb_sys_read,
        .fb_write = dlfb_ops_write,
        .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,
};


/*
 * Assumes &info->lock held by caller
 * Assumes no active clients have framebuffer open
 */
static int dlfb_realloc_framebuffer(struct dlfb_data *dev, struct fb_info *info)
{
        int retval = -ENOMEM;
        int old_len = info->fix.smem_len;
        int new_len;
        unsigned char *old_fb = info->screen_base;
        unsigned char *new_fb;
        unsigned char *new_back = NULL;

        pr_warn("Reallocating framebuffer. Addresses will change!\n");

        new_len = info->fix.line_length * info->var.yres;

        if (PAGE_ALIGN(new_len) > old_len) {
                /*
                 * Alloc system memory for virtual framebuffer
                 */
                new_fb = vmalloc(new_len);
                if (!new_fb) {
                        pr_err("Virtual framebuffer alloc failed\n");
                        goto error;
                }

                if (info->screen_base) {
                        memcpy(new_fb, old_fb, old_len);
                        vfree(info->screen_base);
                }

                info->screen_base = new_fb;
                info->fix.smem_len = PAGE_ALIGN(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)
                        pr_info("No shadow/backing buffer allocated\n");
                else {
                        vfree(dev->backing_buffer);
                        dev->backing_buffer = new_back;
                }
        }

        retval = 0;

error:
        return retval;
}

/*
 * 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 *dev,
                           struct fb_info *info,
                           char *default_edid, size_t default_edid_size)
{
        int i;
        const struct fb_videomode *default_vmode = NULL;
        int result = 0;
        char *edid;
        int tries = 3;

        if (info->dev) /* only use mutex if info has been registered */
                mutex_lock(&info->lock);

        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(dev, edid, EDID_LENGTH);

                if (i >= EDID_LENGTH)
                        fb_edid_to_monspecs(edid, &info->monspecs);

                if (info->monspecs.modedb_len > 0) {
                        dev->edid = edid;
                        dev->edid_size = i;
                        break;
                }
        }

        /* If that fails, use a previously returned EDID if available */
        if (info->monspecs.modedb_len == 0) {

                pr_err("Unable to get valid EDID from device/display\n");

                if (dev->edid) {
                        fb_edid_to_monspecs(dev->edid, &info->monspecs);
                        if (info->monspecs.modedb_len > 0)
                                pr_err("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);
                                dev->edid = edid;
                                dev->edid_size = default_edid_size;
                                pr_err("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++) {
                        if (dlfb_is_valid_mode(&info->monspecs.modedb[i], info))
                                fb_add_videomode(&info->monspecs.modedb[i],
                                        &info->modelist);
                        else {
                                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++) {
                        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);
        }

        /* If we have good mode and no active clients*/
        if ((default_vmode != NULL) && (dev->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));
                info->fix.line_length = info->var.xres *
                        (info->var.bits_per_pixel / 8);

                result = dlfb_realloc_framebuffer(dev, info);

        } else
                result = -EINVAL;

error:
        if (edid && (dev->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 *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 edid_show(
                        struct file *filp,
                        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;

        if (dev->edid == NULL)
                return 0;

        if ((off >= dev->edid_size) || (count > dev->edid_size))
                return 0;

        if (off + count > dev->edid_size)
                count = dev->edid_size - off;

        pr_info("sysfs edid copy %p to %p, %d bytes\n",
                dev->edid, buf, (int) count);

        memcpy(buf, dev->edid, count);

        return count;
}

static ssize_t edid_store(
                        struct file *filp,
                        struct kobject *kobj, struct bin_attribute *a,
                        char *src, loff_t src_off, size_t src_size) {
        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;
        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(dev, fb_info, src, src_size);
        if (ret)
                return ret;

        if (!dev->edid || memcmp(src, dev->edid, src_size))
                return -EINVAL;

        pr_info("sysfs written EDID is new default\n");
        dlfb_ops_set_par(fb_info);
        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 *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);

        return count;
}

static struct bin_attribute edid_attr = {
        .attr.name = "edid",
        .attr.mode = 0666,
        .size = EDID_LENGTH,
        .read = edid_show,
        .write = edid_store
};

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(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 *dev)
{
        int ret;
        void *buf;
        static const u8 set_def_chn[] = {
                                0x57, 0xCD, 0xDC, 0xA7,
                                0x1C, 0x88, 0x5E, 0x15,
                                0x60, 0xFE, 0xC6, 0x97,
                                0x16, 0x3D, 0x47, 0xF2  };

        buf = kmemdup(set_def_chn, sizeof(set_def_chn), GFP_KERNEL);

        if (!buf)
                return -ENOMEM;

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

        kfree(buf);

        return ret;
}

static int dlfb_parse_vendor_descriptor(struct dlfb_data *dev,
                                        struct usb_interface *interface)
{
        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(interface),
                                        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(interface->cur_altsetting,
                        0x5f, &desc))
                        total_len = (int) desc[0];
        }

        if (total_len > 5) {
                pr_info("vendor descriptor length:%x 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) {
                        u8 length;
                        u16 key;

                        key = le16_to_cpu(*((u16 *) desc));
                        desc += sizeof(u16);
                        length = *desc;
                        desc++;

                        switch (key) {
                        case 0x0200: { /* max_area */
                                u32 max_area;
                                max_area = le32_to_cpu(*((u32 *)desc));
                                pr_warn("DL chip limited to %d pixel modes\n",
                                        max_area);
                                dev->sku_pixel_limit = max_area;
                                break;
                        }
                        default:
                                break;
                        }
                        desc += length;
                }
        } else {
                pr_info("vendor descriptor not available (%d)\n", total_len);
        }

        goto success;

unrecognized:
        /* allow udlfb to load for now even if firmware unrecognized */
        pr_err("Unrecognized vendor firmware descriptor\n");

success:
        kfree(buf);
        return true;
}

static void dlfb_init_framebuffer_work(struct work_struct *work);

static int dlfb_usb_probe(struct usb_interface *interface,
                        const struct usb_device_id *id)
{
        struct usb_device *usbdev;
        struct dlfb_data *dev;
        int retval = -ENOMEM;

        /* usb initialization */

        usbdev = interface_to_usbdev(interface);

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

        kref_init(&dev->kref); /* matching kref_put in usb .disconnect fn */

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

        pr_info("%s %s - serial #%s\n",
                usbdev->manufacturer, usbdev->product, usbdev->serial);
        pr_info("vid_%04x&pid_%04x&rev_%04x driver's dlfb_data struct at %p\n",
                le16_to_cpu(usbdev->descriptor.idVendor),
                le16_to_cpu(usbdev->descriptor.idProduct),
                le16_to_cpu(usbdev->descriptor.bcdDevice), dev);
        pr_info("console enable=%d\n", console);
        pr_info("fb_defio enable=%d\n", fb_defio);
        pr_info("shadow enable=%d\n", shadow);

        dev->sku_pixel_limit = 2048 * 1152; /* default to maximum */

        if (!dlfb_parse_vendor_descriptor(dev, interface)) {
                pr_err("firmware not recognized. Assume incompatible device\n");
                goto error;
        }

        if (pixel_limit) {
                pr_warn("DL chip limit of %d overridden"
                        " by module param to %d\n",
                        dev->sku_pixel_limit, pixel_limit);
                dev->sku_pixel_limit = pixel_limit;
        }


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

        kref_get(&dev->kref); /* matching kref_put in free_framebuffer_work */

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

        /* Workitem keep things fast & simple during USB enumeration */
        INIT_DELAYED_WORK(&dev->init_framebuffer_work,
                          dlfb_init_framebuffer_work);
        schedule_delayed_work(&dev->init_framebuffer_work, 0);

        return 0;

error:
        if (dev) {

                kref_put(&dev->kref, dlfb_free); /* ref for framebuffer */
                kref_put(&dev->kref, dlfb_free); /* last ref from kref_init */

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

        return retval;
}

static void dlfb_init_framebuffer_work(struct work_struct *work)
{
        struct dlfb_data *dev = container_of(work, struct dlfb_data,
                                             init_framebuffer_work.work);
        struct fb_info *info;
        int retval;
        int i;

        /* allocates framebuffer driver structure, not framebuffer memory */
        info = framebuffer_alloc(0, dev->gdev);
        if (!info) {
                pr_err("framebuffer_alloc failed\n");
                goto error;
        }

        dev->info = info;
        info->par = dev;
        info->pseudo_palette = dev->pseudo_palette;
        info->fbops = &dlfb_ops;

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

        INIT_DELAYED_WORK(&dev->free_framebuffer_work,
                          dlfb_free_framebuffer_work);

        INIT_LIST_HEAD(&info->modelist);

        retval = dlfb_setup_modes(dev, info, NULL, 0);
        if (retval != 0) {
                pr_err("unable to find common mode for display and adapter\n");
                goto error;
        }

        /* ready to begin using device */

        atomic_set(&dev->usb_active, 1);
        dlfb_select_std_channel(dev);

        dlfb_ops_check_var(&info->var, info);
        dlfb_ops_set_par(info);

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

        for (i = 0; i < ARRAY_SIZE(fb_device_attrs); i++) {
                retval = device_create_file(info->dev, &fb_device_attrs[i]);
                if (retval) {
                        pr_warn("device_create_file failed %d\n", retval);
                }
        }

        retval = device_create_bin_file(info->dev, &edid_attr);
        if (retval) {
                pr_warn("device_create_bin_file failed %d\n", retval);
        }

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

error:
        dlfb_free_framebuffer(dev);
}

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;

        pr_info("USB disconnect starting\n");

        /* we virtualize until all fb clients release. Then we free */
        dev->virtualized = true;

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

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

        if (info) {
                /* 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);
                unlink_framebuffer(info);
        }

        usb_set_intfdata(interface, NULL);
        dev->udev = NULL;
        dev->gdev = NULL;

        /* if clients still have us open, will be freed on last close */
        if (dev->fb_count == 0)
                schedule_delayed_work(&dev->free_framebuffer_work, 0);

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

        /* 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,
};

module_usb_driver(dlfb_driver);

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)) {
                        pr_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);

        /*
         * When using fb_defio, we deadlock if up() is called
         * while another is waiting. So queue to another process.
         */
        if (fb_defio)
                schedule_delayed_work(&unode->release_urb_work, 0);
        else
                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;

        pr_notice("Freeing all render urbs\n");

        /* keep waiting and freeing, until we've got 'em all */
        while (count--) {

                /* Getting interrupted means a leak, but ok at disconnect */
                ret = down_interruptible(&dev->urbs.limit_sem);
                if (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_free_coherent(urb->dev, dev->urbs.size,
                                  urb->transfer_buffer, urb->transfer_dma);
                usb_free_urb(urb);
                kfree(node);
        }

        dev->urbs.count = 0;
}

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;

                INIT_DELAYED_WORK(&unode->release_urb_work,
                          dlfb_release_urb_work);

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

                buf = usb_alloc_coherent(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;

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

        return i;
}

static struct urb *dlfb_get_urb(struct dlfb_data *dev)
{
        int ret;
        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);
                pr_warn("wait for urb interrupted: %x available: %d\n",
                       ret, dev->urbs.available);
                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);
                pr_err("usb_submit_urb error %x\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");