drivers/w1-eeprom/ds2502.c

   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 */
  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
  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
 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  */
 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
 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
 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 };