1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3 * Driver for DS-2502 One wire "Add only Memory".
4 *
5 * The chip has 4 pages of 32 bytes.
6 * In addition it has 8 out of band status bytes that are used, by software,
7 * as page redirection bytes by an algorithm described in the data sheet.
8 * This is useful since data cannot be erased once written but it can be
9 * "patched" up to four times by switching pages.
10 *
11 * So, when a read request is entirely in the first page automatically
12 * apply the page redirection bytes (which allows the device to be seen as
13 * a 32 byte PROM, writable 4 times).
14 *
15 * If the read request is outside of or larger than the first page then read
16 * the raw data (which allows the device to be seen as a 128 byte PROM,
17 * writable once).
18 *
19 * Copyright (c) 2018 Flowbird
20 * Martin Fuzzey <martin.fuzzey@flowbird.group>
21 */
22
23 #include <common.h>
24 #include <dm.h>
25 #include <linux/err.h>
26 #include <w1-eeprom.h>
27 #include <w1.h>
28
29 #define DS2502_PAGE_SIZE 32
30 #define DS2502_PAGE_COUNT 4
31 #define DS2502_STATUS_SIZE 8
32
33 #define DS2502_CMD_READ_STATUS 0xAA
34 #define DS2502_CMD_READ_GEN_CRC 0xC3
35
36 /* u-boot crc8() is CCITT CRC8, we need x^8 + x^5 + x^4 + 1 LSB first */
ds2502_crc8(const u8 * buf,int len)37 static unsigned int ds2502_crc8(const u8 *buf, int len)
38 {
39 static const u8 poly = 0x8C; /* (1 + x^4 + x^5) + x^8 */
40 u8 crc = 0;
41 int i;
42
43 for (i = 0; i < len; i++) {
44 u8 data = buf[i];
45 int j;
46
47 for (j = 0; j < 8; j++) {
48 u8 mix = (crc ^ data) & 1;
49
50 crc >>= 1;
51 if (mix)
52 crc ^= poly;
53 data >>= 1;
54 }
55 }
56 return crc;
57 }
58
ds2502_read(struct udevice * dev,u8 cmd,int bytes_in_page,int pos,u8 * buf,int bytes_for_user)59 static int ds2502_read(struct udevice *dev, u8 cmd,
60 int bytes_in_page, int pos,
61 u8 *buf, int bytes_for_user)
62 {
63 int retry;
64 int ret = 0;
65
66 for (retry = 0; retry < 3; retry++) {
67 u8 pagebuf[DS2502_PAGE_SIZE + 1]; /* 1 byte for CRC8 */
68 u8 crc;
69 int i;
70
71 ret = w1_reset_select(dev);
72 if (ret)
73 return ret;
74
75 /* send read to end of page and generate CRC command */
76 pagebuf[0] = cmd;
77 pagebuf[1] = pos & 0xff;
78 pagebuf[2] = pos >> 8;
79 crc = ds2502_crc8(pagebuf, 3);
80 for (i = 0; i < 3; i++)
81 w1_write_byte(dev, pagebuf[i]);
82
83 /* Check command CRC */
84 ret = w1_read_byte(dev);
85 if (ret < 0) {
86 dev_dbg(dev, "Error %d reading command CRC\n", ret);
87 continue;
88 }
89
90 if (ret != crc) {
91 dev_dbg(dev,
92 "bad CRC8 for cmd %02x got=%02X exp=%02X\n",
93 cmd, ret, crc);
94 ret = -EIO;
95 continue;
96 }
97
98 /* read data and check CRC */
99 ret = w1_read_buf(dev, pagebuf, bytes_in_page + 1);
100 if (ret < 0) {
101 dev_dbg(dev, "Error %d reading data\n", ret);
102 continue;
103 }
104
105 crc = ds2502_crc8(pagebuf, bytes_in_page);
106 if (crc == pagebuf[bytes_in_page]) {
107 memcpy(buf, pagebuf, bytes_for_user);
108 ret = 0;
109 break;
110 }
111 dev_dbg(dev, "Bad CRC8 got=%02X exp=%02X pos=%04X\n",
112 pagebuf[bytes_in_page], crc, pos);
113 ret = -EIO;
114 }
115
116 return ret;
117 }
118
ds2502_read_status_bytes(struct udevice * dev,u8 * buf)119 static inline int ds2502_read_status_bytes(struct udevice *dev, u8 *buf)
120 {
121 return ds2502_read(dev, DS2502_CMD_READ_STATUS,
122 DS2502_STATUS_SIZE, 0,
123 buf, DS2502_STATUS_SIZE);
124 }
125
126 /*
127 * Status bytes (from index 1) contain 1's complement page indirection
128 * So for N writes:
129 * N=1: ff ff ff ff ff ff ff 00
130 * N=2: ff fe ff ff ff ff ff 00
131 * N=3: ff fe fd ff ff ff ff 00
132 * N=4: ff fe fd fc ff ff ff 00
133 */
ds2502_indirect_page(struct udevice * dev,u8 * status,int page)134 static int ds2502_indirect_page(struct udevice *dev, u8 *status, int page)
135 {
136 int page_seen = 0;
137
138 do {
139 u8 sb = status[page + 1];
140
141 if (sb == 0xff)
142 break;
143
144 page = ~sb & 0xff;
145
146 if (page >= DS2502_PAGE_COUNT) {
147 dev_err(dev,
148 "Illegal page redirection status byte %02x\n",
149 sb);
150 return -EINVAL;
151 }
152
153 if (page_seen & (1 << page)) {
154 dev_err(dev, "Infinite loop in page redirection\n");
155 return -EINVAL;
156 }
157
158 page_seen |= (1 << page);
159 } while (1);
160
161 return page;
162 }
163
ds2502_read_buf(struct udevice * dev,unsigned int offset,u8 * buf,unsigned int count)164 static int ds2502_read_buf(struct udevice *dev, unsigned int offset,
165 u8 *buf, unsigned int count)
166 {
167 unsigned int min_page = offset / DS2502_PAGE_SIZE;
168 unsigned int max_page = (offset + count - 1) / DS2502_PAGE_SIZE;
169 int xfered = 0;
170 u8 status_bytes[DS2502_STATUS_SIZE];
171 int i;
172 int ret;
173
174 if (min_page >= DS2502_PAGE_COUNT || max_page >= DS2502_PAGE_COUNT)
175 return -EINVAL;
176
177 if (min_page == 0 && max_page == 0) {
178 ret = ds2502_read_status_bytes(dev, status_bytes);
179 if (ret)
180 return ret;
181 } else {
182 /* Dummy one to one page redirection */
183 memset(status_bytes, 0xff, sizeof(status_bytes));
184 }
185
186 for (i = min_page; i <= max_page; i++) {
187 int page;
188 int pos;
189 int bytes_in_page;
190 int bytes_for_user;
191
192 page = ds2502_indirect_page(dev, status_bytes, i);
193 if (page < 0)
194 return page;
195 dev_dbg(dev, "page logical %d => physical %d\n", i, page);
196
197 pos = page * DS2502_PAGE_SIZE;
198 if (i == min_page)
199 pos += offset % DS2502_PAGE_SIZE;
200
201 bytes_in_page = DS2502_PAGE_SIZE - (pos % DS2502_PAGE_SIZE);
202
203 if (i == max_page)
204 bytes_for_user = count - xfered;
205 else
206 bytes_for_user = bytes_in_page;
207
208 ret = ds2502_read(dev, DS2502_CMD_READ_GEN_CRC,
209 bytes_in_page, pos,
210 &buf[xfered], bytes_for_user);
211 if (ret < 0)
212 return ret;
213
214 xfered += bytes_for_user;
215 }
216
217 return 0;
218 }
219
ds2502_probe(struct udevice * dev)220 static int ds2502_probe(struct udevice *dev)
221 {
222 struct w1_device *w1;
223
224 w1 = dev_get_parent_platdata(dev);
225 w1->id = 0;
226 return 0;
227 }
228
229 static const struct w1_eeprom_ops ds2502_ops = {
230 .read_buf = ds2502_read_buf,
231 };
232
233 static const struct udevice_id ds2502_id[] = {
234 { .compatible = "maxim,ds2502", .data = W1_FAMILY_DS2502 },
235 { },
236 };
237
238 U_BOOT_DRIVER(ds2502) = {
239 .name = "ds2502",
240 .id = UCLASS_W1_EEPROM,
241 .of_match = ds2502_id,
242 .ops = &ds2502_ops,
243 .probe = ds2502_probe,
244 };
245