1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * Copyright (C) 2012 Red Hat
  4 * based in parts on udlfb.c:
  5 * Copyright (C) 2009 Roberto De Ioris <roberto@unbit.it>
  6 * Copyright (C) 2009 Jaya Kumar <jayakumar.lkml@gmail.com>
  7 * Copyright (C) 2009 Bernie Thompson <bernie@plugable.com>
  8 */
  9
 10#include <linux/unaligned.h>
 11
 12#include "udl_drv.h"
 13#include "udl_proto.h"
 14
 15#define MAX_CMD_PIXELS		255
 16
 17#define RLX_HEADER_BYTES	7
 18#define MIN_RLX_PIX_BYTES       4
 19#define MIN_RLX_CMD_BYTES	(RLX_HEADER_BYTES + MIN_RLX_PIX_BYTES)
 20
 21#define RLE_HEADER_BYTES	6
 22#define MIN_RLE_PIX_BYTES	3
 23#define MIN_RLE_CMD_BYTES	(RLE_HEADER_BYTES + MIN_RLE_PIX_BYTES)
 24
 25#define RAW_HEADER_BYTES	6
 26#define MIN_RAW_PIX_BYTES	2
 27#define MIN_RAW_CMD_BYTES	(RAW_HEADER_BYTES + MIN_RAW_PIX_BYTES)
 28
 29static inline u16 pixel32_to_be16(const uint32_t pixel)
 30{
 31	return (((pixel >> 3) & 0x001f) |
 32		((pixel >> 5) & 0x07e0) |
 33		((pixel >> 8) & 0xf800));
 34}
 35
 36static inline u16 get_pixel_val16(const uint8_t *pixel, int log_bpp)
 37{
 38	u16 pixel_val16;
 39	if (log_bpp == 1)
 40		pixel_val16 = *(const uint16_t *)pixel;
 41	else
 42		pixel_val16 = pixel32_to_be16(*(const uint32_t *)pixel);
 43	return pixel_val16;
 44}
 45
 46/*
 47 * Render a command stream for an encoded horizontal line segment of pixels.
 48 *
 49 * A command buffer holds several commands.
 50 * It always begins with a fresh command header
 51 * (the protocol doesn't require this, but we enforce it to allow
 52 * multiple buffers to be potentially encoded and sent in parallel).
 53 * A single command encodes one contiguous horizontal line of pixels
 54 *
 55 * The function relies on the client to do all allocation, so that
 56 * rendering can be done directly to output buffers (e.g. USB URBs).
 57 * The function fills the supplied command buffer, providing information
 58 * on where it left off, so the client may call in again with additional
 59 * buffers if the line will take several buffers to complete.
 60 *
 61 * A single command can transmit a maximum of 256 pixels,
 62 * regardless of the compression ratio (protocol design limit).
 63 * To the hardware, 0 for a size byte means 256
 64 *
 65 * Rather than 256 pixel commands which are either rl or raw encoded,
 66 * the rlx command simply assumes alternating raw and rl spans within one cmd.
 67 * This has a slightly larger header overhead, but produces more even results.
 68 * It also processes all data (read and write) in a single pass.
 69 * Performance benchmarks of common cases show it having just slightly better
 70 * compression than 256 pixel raw or rle commands, with similar CPU consumpion.
 71 * But for very rl friendly data, will compress not quite as well.
 72 */
 73static void udl_compress_hline16(
 74	const u8 **pixel_start_ptr,
 75	const u8 *const pixel_end,
 76	uint32_t *device_address_ptr,
 77	uint8_t **command_buffer_ptr,
 78	const uint8_t *const cmd_buffer_end, int log_bpp)
 79{
 80	const int bpp = 1 << log_bpp;
 81	const u8 *pixel = *pixel_start_ptr;
 82	uint32_t dev_addr  = *device_address_ptr;
 83	uint8_t *cmd = *command_buffer_ptr;
 84
 85	while ((pixel_end > pixel) &&
 86	       (cmd_buffer_end - MIN_RLX_CMD_BYTES > cmd)) {
 87		uint8_t *raw_pixels_count_byte = NULL;
 88		uint8_t *cmd_pixels_count_byte = NULL;
 89		const u8 *raw_pixel_start = NULL;
 90		const u8 *cmd_pixel_start, *cmd_pixel_end = NULL;
 91		uint16_t pixel_val16;
 92
 93		*cmd++ = UDL_MSG_BULK;
 94		*cmd++ = UDL_CMD_WRITERLX16;
 95		*cmd++ = (uint8_t) ((dev_addr >> 16) & 0xFF);
 96		*cmd++ = (uint8_t) ((dev_addr >> 8) & 0xFF);
 97		*cmd++ = (uint8_t) ((dev_addr) & 0xFF);
 98
 99		cmd_pixels_count_byte = cmd++; /*  we'll know this later */
100		cmd_pixel_start = pixel;
101
102		raw_pixels_count_byte = cmd++; /*  we'll know this later */
103		raw_pixel_start = pixel;
104
105		cmd_pixel_end = pixel + (min3(MAX_CMD_PIXELS + 1UL,
106					(unsigned long)(pixel_end - pixel) >> log_bpp,
107					(unsigned long)(cmd_buffer_end - 1 - cmd) / 2) << log_bpp);
108
109		pixel_val16 = get_pixel_val16(pixel, log_bpp);
110
111		while (pixel < cmd_pixel_end) {
112			const u8 *const start = pixel;
113			const uint16_t repeating_pixel_val16 = pixel_val16;
114
115			put_unaligned_be16(pixel_val16, cmd);
116
117			cmd += 2;
118			pixel += bpp;
119
120			while (pixel < cmd_pixel_end) {
121				pixel_val16 = get_pixel_val16(pixel, log_bpp);
122				if (pixel_val16 != repeating_pixel_val16)
123					break;
124				pixel += bpp;
125			}
126
127			if (unlikely(pixel > start + bpp)) {
128				/* go back and fill in raw pixel count */
129				*raw_pixels_count_byte = (((start -
130						raw_pixel_start) >> log_bpp) + 1) & 0xFF;
131
132				/* immediately after raw data is repeat byte */
133				*cmd++ = (((pixel - start) >> log_bpp) - 1) & 0xFF;
134
135				/* Then start another raw pixel span */
136				raw_pixel_start = pixel;
137				raw_pixels_count_byte = cmd++;
138			}
139		}
140
141		if (pixel > raw_pixel_start) {
142			/* finalize last RAW span */
143			*raw_pixels_count_byte = ((pixel - raw_pixel_start) >> log_bpp) & 0xFF;
144		} else {
145			/* undo unused byte */
146			cmd--;
147		}
148
149		*cmd_pixels_count_byte = ((pixel - cmd_pixel_start) >> log_bpp) & 0xFF;
150		dev_addr += ((pixel - cmd_pixel_start) >> log_bpp) * 2;
151	}
152
153	if (cmd_buffer_end <= MIN_RLX_CMD_BYTES + cmd) {
154		/* Fill leftover bytes with no-ops */
155		if (cmd_buffer_end > cmd)
156			memset(cmd, UDL_MSG_BULK, cmd_buffer_end - cmd);
157		cmd = (uint8_t *) cmd_buffer_end;
158	}
159
160	*command_buffer_ptr = cmd;
161	*pixel_start_ptr = pixel;
162	*device_address_ptr = dev_addr;
163
164	return;
165}
166
167/*
168 * There are 3 copies of every pixel: The front buffer that the fbdev
169 * client renders to, the actual framebuffer across the USB bus in hardware
170 * (that we can only write to, slowly, and can never read), and (optionally)
171 * our shadow copy that tracks what's been sent to that hardware buffer.
172 */
173int udl_render_hline(struct drm_device *dev, int log_bpp, struct urb **urb_ptr,
174		     const char *front, char **urb_buf_ptr,
175		     u32 byte_offset, u32 device_byte_offset,
176		     u32 byte_width)
177{
178	const u8 *line_start, *line_end, *next_pixel;
179	u32 base16 = 0 + (device_byte_offset >> log_bpp) * 2;
180	struct urb *urb = *urb_ptr;
181	u8 *cmd = *urb_buf_ptr;
182	u8 *cmd_end = (u8 *) urb->transfer_buffer + urb->transfer_buffer_length;
183
184	if (WARN_ON(!(log_bpp == 1 || log_bpp == 2))) {
185		/* need to finish URB at error from this function */
186		udl_urb_completion(urb);
187		return -EINVAL;
188	}
189
190	line_start = (u8 *) (front + byte_offset);
191	next_pixel = line_start;
192	line_end = next_pixel + byte_width;
193
194	while (next_pixel < line_end) {
195
196		udl_compress_hline16(&next_pixel,
197			     line_end, &base16,
198			     (u8 **) &cmd, (u8 *) cmd_end, log_bpp);
199
200		if (cmd >= cmd_end) {
201			int len = cmd - (u8 *) urb->transfer_buffer;
202			int ret = udl_submit_urb(dev, urb, len);
203			if (ret)
204				return ret;
205			urb = udl_get_urb(dev);
206			if (!urb)
207				return -EAGAIN;
208			*urb_ptr = urb;
209			cmd = urb->transfer_buffer;
210			cmd_end = &cmd[urb->transfer_buffer_length];
211		}
212	}
213
214	*urb_buf_ptr = cmd;
215
216	return 0;
217}