xref: /openbmc/linux/drivers/gpu/drm/udl/udl_transfer.c (revision 1b8db07f)
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 <asm/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 
pixel32_to_be16(const uint32_t pixel)29 static 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 
get_pixel_val16(const uint8_t * pixel,int log_bpp)36 static 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  */
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)73 static 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  */
udl_render_hline(struct drm_device * dev,int log_bpp,struct urb ** urb_ptr,const char * front,char ** urb_buf_ptr,u32 byte_offset,u32 device_byte_offset,u32 byte_width)173 int 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 }
218