udl_transfer.c

Go to the documentation of this file.

/*
 * Copyright (C) 2012 Red Hat
 * based in parts on udlfb.c:
 * 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.
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/fb.h>
#include <linux/prefetch.h>

#include <drm/drmP.h>
#include "udl_drv.h"

#define MAX_CMD_PIXELS      255

#define RLX_HEADER_BYTES    7
#define MIN_RLX_PIX_BYTES       4
#define MIN_RLX_CMD_BYTES   (RLX_HEADER_BYTES + MIN_RLX_PIX_BYTES)

#define RLE_HEADER_BYTES    6
#define MIN_RLE_PIX_BYTES   3
#define MIN_RLE_CMD_BYTES   (RLE_HEADER_BYTES + MIN_RLE_PIX_BYTES)

#define RAW_HEADER_BYTES    6
#define MIN_RAW_PIX_BYTES   2
#define MIN_RAW_CMD_BYTES   (RAW_HEADER_BYTES + MIN_RAW_PIX_BYTES)

/*
 * 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
 */
#if 0
static int udl_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);
}
#endif

static inline u16 pixel32_to_be16p(const uint8_t *pixel)
{
    uint32_t pix = *(uint32_t *)pixel;
    u16 retval;

    retval =  (((pix >> 3) & 0x001f) |
           ((pix >> 5) & 0x07e0) |
           ((pix >> 8) & 0xf800));
    return retval;
}

/*
 * 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 udl_compress_hline16(
    const u8 **pixel_start_ptr,
    const u8 *const pixel_end,
    uint32_t *device_address_ptr,
    uint8_t **command_buffer_ptr,
    const uint8_t *const cmd_buffer_end, int bpp)
{
    const u8 *pixel = *pixel_start_ptr;
    uint32_t dev_addr  = *device_address_ptr;
    uint8_t *cmd = *command_buffer_ptr;

    while ((pixel_end > pixel) &&
           (cmd_buffer_end - MIN_RLX_CMD_BYTES > cmd)) {
        uint8_t *raw_pixels_count_byte = NULL;
        uint8_t *cmd_pixels_count_byte = NULL;
        const u8 *raw_pixel_start = NULL;
        const u8 *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) / bpp,
                (int)(cmd_buffer_end - cmd) / 2))) * bpp;

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

        while (pixel < cmd_pixel_end) {
            const u8 * const repeating_pixel = pixel;

            if (bpp == 2)
                *(uint16_t *)cmd = cpu_to_be16p((uint16_t *)pixel);
            else if (bpp == 4)
                *(uint16_t *)cmd = cpu_to_be16(pixel32_to_be16p(pixel));

            cmd += 2;
            pixel += bpp;

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

                while ((pixel < cmd_pixel_end)
                       && (!memcmp(pixel, repeating_pixel, bpp))) {
                    pixel += bpp;
                }

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

        *cmd_pixels_count_byte = ((pixel - cmd_pixel_start) / bpp) & 0xFF;
        dev_addr += ((pixel - cmd_pixel_start) / bpp) * 2;
    }

    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.
 */
int udl_render_hline(struct drm_device *dev, int bpp, struct urb **urb_ptr,
             const char *front, char **urb_buf_ptr,
             u32 byte_offset, u32 device_byte_offset,
             u32 byte_width,
             int *ident_ptr, int *sent_ptr)
{
    const u8 *line_start, *line_end, *next_pixel;
    u32 base16 = 0 + (device_byte_offset / bpp) * 2;
    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;

    while (next_pixel < line_end) {

        udl_compress_hline16(&next_pixel,
                 line_end, &base16,
                 (u8 **) &cmd, (u8 *) cmd_end, bpp);

        if (cmd >= cmd_end) {
            int len = cmd - (u8 *) urb->transfer_buffer;
            if (udl_submit_urb(dev, urb, len))
                return 1; /* lost pixels is set */
            *sent_ptr += len;
            urb = udl_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;
}