// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2012 Red Hat
 * based in parts on udlfb.c:
 * 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>
 */

#include <linux/unaligned.h>

#include "udl_drv.h"
#include "udl_proto.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)

static inline u16 pixel32_to_be16(const uint32_t pixel)
{
        return (((pixel >> 3) & 0x001f) |
                ((pixel >> 5) & 0x07e0) |
                ((pixel >> 8) & 0xf800));
}

static inline u16 get_pixel_val16(const uint8_t *pixel, int log_bpp)
{
        u16 pixel_val16;
        if (log_bpp == 1)
                pixel_val16 = *(const uint16_t *)pixel;
        else
                pixel_val16 = pixel32_to_be16(*(const uint32_t *)pixel);
        return pixel_val16;
}

/*
 * 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 log_bpp)
{
        const int bpp = 1 << log_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;
                uint16_t pixel_val16;

                *cmd++ = UDL_MSG_BULK;
                *cmd++ = UDL_CMD_WRITERLX16;
                *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 + (min3(MAX_CMD_PIXELS + 1UL,
                                        (unsigned long)(pixel_end - pixel) >> log_bpp,
                                        (unsigned long)(cmd_buffer_end - 1 - cmd) / 2) << log_bpp);

                pixel_val16 = get_pixel_val16(pixel, log_bpp);

                while (pixel < cmd_pixel_end) {
                        const u8 *const start = pixel;
                        const uint16_t repeating_pixel_val16 = pixel_val16;

                        put_unaligned_be16(pixel_val16, cmd);

                        cmd += 2;
                        pixel += bpp;

                        while (pixel < cmd_pixel_end) {
                                pixel_val16 = get_pixel_val16(pixel, log_bpp);
                                if (pixel_val16 != repeating_pixel_val16)
                                        break;
                                pixel += bpp;
                        }

                        if (unlikely(pixel > start + bpp)) {
                                /* go back and fill in raw pixel count */
                                *raw_pixels_count_byte = (((start -
                                                raw_pixel_start) >> log_bpp) + 1) & 0xFF;

                                /* immediately after raw data is repeat byte */
                                *cmd++ = (((pixel - start) >> log_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) >> log_bpp) & 0xFF;
                } else {
                        /* undo unused byte */
                        cmd--;
                }

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

        if (cmd_buffer_end <= MIN_RLX_CMD_BYTES + cmd) {
                /* Fill leftover bytes with no-ops */
                if (cmd_buffer_end > cmd)
                        memset(cmd, UDL_MSG_BULK, 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 udl_device *udl, int log_bpp, struct urb **urb_ptr,
                     const char *front, char **urb_buf_ptr,
                     u32 byte_offset, u32 device_byte_offset,
                     u32 byte_width)
{
        const u8 *line_start, *line_end, *next_pixel;
        u32 base16 = 0 + (device_byte_offset >> log_bpp) * 2;
        struct urb *urb = *urb_ptr;
        u8 *cmd = *urb_buf_ptr;
        u8 *cmd_end = (u8 *) urb->transfer_buffer + urb->transfer_buffer_length;

        if (WARN_ON(!(log_bpp == 1 || log_bpp == 2))) {
                /* need to finish URB at error from this function */
                udl_urb_completion(urb);
                return -EINVAL;
        }

        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, log_bpp);

                if (cmd >= cmd_end) {
                        int len = cmd - (u8 *) urb->transfer_buffer;
                        int ret = udl_submit_urb(udl, urb, len);
                        if (ret)
                                return ret;
                        urb = udl_get_urb(udl);
                        if (!urb)
                                return -EAGAIN;
                        *urb_ptr = urb;
                        cmd = urb->transfer_buffer;
                        cmd_end = &cmd[urb->transfer_buffer_length];
                }
        }

        *urb_buf_ptr = cmd;

        return 0;
}