udlfb.c

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/*
 * udlfb.c -- Framebuffer driver for DisplayLink USB controller
 *
 * Copyright (C) 2009 Roberto De Ioris <[email protected]>
 * Copyright (C) 2009 Jaya Kumar <[email protected]>
 * Copyright (C) 2009 Bernie Thompson <[email protected]>
 *
 * 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 = 0;
    int writesize;
    struct urb *urb;

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

    urb = dlfb_get_urb(dev);
    if (!urb)
        return -ENOMEM;

    buf = (char *) urb->transfer_buffer;

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

    wrptr = dlfb_set_vid_cmds(wrptr, var);
    wrptr = dlfb_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 (offset + size > info->fix.smem_len)
        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 = 0;
        uint8_t *cmd_pixels_count_byte = 0;
        const uint16_t *raw_pixel_start = 0;
        const uint16_t *cmd_pixel_start, *cmd_pixel_end = 0;

        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;
}

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);

    if (dev->backing_buffer)
        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);
        if (info->screen_base)
            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_info("/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 = 0;

    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 {
            if (dev->backing_buffer)
                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;
    u8 set_def_chn[] = {       0x57, 0xCD, 0xDC, 0xA7,
                0x1C, 0x88, 0x5E, 0x15,
                0x60, 0xFE, 0xC6, 0x97,
                0x16, 0x3D, 0x47, 0xF2  };

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

static int dlfb_parse_vendor_descriptor(struct dlfb_data *dev,
                    struct usb_interface *interface)
{
    char *desc;
    char *buf;
    char *desc_end;

    int total_len = 0;

    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:%02x %02x %02x %02x" \
            "%02x %02x %02x %02x %02x %02x %02x\n",
            total_len, desc[0],
            desc[1], desc[2], desc[3], desc[4], desc[5], desc[6],
            desc[7], desc[8], desc[9], desc[10]);

        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 = 0;
    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",
        usbdev->descriptor.idVendor, usbdev->descriptor.idProduct,
        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 overriden"
            " 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) {
        retval = -ENOMEM;
        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 = 0;
    struct list_head *entry;
    struct urb_node *unode;
    struct urb *urb = NULL;
    unsigned long flags;

    /* Wait for an in-flight buffer to complete and get re-queued */
    ret = down_timeout(&dev->urbs.limit_sem, GET_URB_TIMEOUT);
    if (ret) {
        atomic_set(&dev->lost_pixels, 1);
        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 <[email protected]>, "
          "Jaya Kumar <[email protected]>, "
          "Bernie Thompson <[email protected]>");
MODULE_DESCRIPTION("DisplayLink kernel framebuffer driver");
MODULE_LICENSE("GPL");