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 <[email protected]>
  21  */
  22
  23 #include <common.h>
  24 #include <dm.h>
  25 #include <dm/device_compat.h>
  26 #include <linux/err.h>
  27 #include <w1-eeprom.h>
  28 #include <w1.h>
  29
  30 #define DS2502_PAGE_SIZE        32
  31 #define DS2502_PAGE_COUNT       4
  32 #define DS2502_STATUS_SIZE      8
  33
  34 #define DS2502_CMD_READ_STATUS  0xAA
  35 #define DS2502_CMD_READ_GEN_CRC 0xC3
  36
  37 /* u-boot crc8() is CCITT CRC8, we need x^8 + x^5 + x^4 + 1 LSB first */
  38 static unsigned int ds2502_crc8(const u8 *buf, int len)
  39 {
  40         static const u8 poly = 0x8C;  /* (1 + x^4 + x^5) + x^8 */
  41         u8 crc = 0;
  42         int i;
  43
  44         for (i = 0; i < len; i++) {
  45                 u8 data = buf[i];
  46                 int j;
  47
  48                 for (j = 0; j < 8; j++) {
  49                         u8 mix = (crc ^ data) & 1;
  50
  51                         crc >>= 1;
  52                         if (mix)
  53                                 crc ^= poly;
  54                         data >>= 1;
  55                 }
  56         }
  57         return crc;
  58 }
  59
  60 static int ds2502_read(struct udevice *dev, u8 cmd,
  61                        int bytes_in_page, int pos,
  62                        u8 *buf, int bytes_for_user)
  63 {
  64         int retry;
  65         int ret = 0;
  66
  67         for (retry = 0; retry < 3; retry++) {
  68                 u8 pagebuf[DS2502_PAGE_SIZE + 1]; /* 1 byte for CRC8 */
  69                 u8 crc;
  70                 int i;
  71
  72                 ret = w1_reset_select(dev);
  73                 if (ret)
  74                         return ret;
  75
  76                 /* send read to end of page and generate CRC command */
  77                 pagebuf[0] = cmd;
  78                 pagebuf[1] = pos & 0xff;
  79                 pagebuf[2] = pos >> 8;
  80                 crc = ds2502_crc8(pagebuf, 3);
  81                 for (i = 0; i < 3; i++)
  82                         w1_write_byte(dev, pagebuf[i]);
  83
  84                 /* Check command CRC */
  85                 ret = w1_read_byte(dev);
  86                 if (ret < 0) {
  87                         dev_dbg(dev, "Error %d reading command CRC\n", ret);
  88                         continue;
  89                 }
  90
  91                 if (ret != crc) {
  92                         dev_dbg(dev,
  93                                 "bad CRC8 for cmd %02x got=%02X exp=%02X\n",
  94                                 cmd, ret, crc);
  95                         ret = -EIO;
  96                         continue;
  97                 }
  98
  99                 /* read data and check CRC */
 100                 ret = w1_read_buf(dev, pagebuf, bytes_in_page + 1);
 101                 if (ret < 0) {
 102                         dev_dbg(dev, "Error %d reading data\n", ret);
 103                         continue;
 104                 }
 105
 106                 crc = ds2502_crc8(pagebuf, bytes_in_page);
 107                 if (crc == pagebuf[bytes_in_page]) {
 108                         memcpy(buf, pagebuf, bytes_for_user);
 109                         ret = 0;
 110                         break;
 111                 }
 112                 dev_dbg(dev, "Bad CRC8 got=%02X exp=%02X pos=%04X\n",
 113                         pagebuf[bytes_in_page], crc, pos);
 114                 ret = -EIO;
 115         }
 116
 117         return ret;
 118 }
 119
 120 static inline int ds2502_read_status_bytes(struct udevice *dev, u8 *buf)
 121 {
 122         return ds2502_read(dev, DS2502_CMD_READ_STATUS,
 123                                 DS2502_STATUS_SIZE, 0,
 124                                 buf, DS2502_STATUS_SIZE);
 125 }
 126
 127 /*
 128  * Status bytes (from index 1) contain 1's complement page indirection
 129  * So for N writes:
 130  * N=1: ff ff ff ff ff ff ff 00
 131  * N=2: ff fe ff ff ff ff ff 00
 132  * N=3: ff fe fd ff ff ff ff 00
 133  * N=4: ff fe fd fc ff ff ff 00
 134  */
 135 static int ds2502_indirect_page(struct udevice *dev, u8 *status, int page)
 136 {
 137         int page_seen = 0;
 138
 139         do {
 140                 u8 sb = status[page + 1];
 141
 142                 if (sb == 0xff)
 143                         break;
 144
 145                 page = ~sb & 0xff;
 146
 147                 if (page >= DS2502_PAGE_COUNT) {
 148                         dev_err(dev,
 149                                 "Illegal page redirection status byte %02x\n",
 150                                 sb);
 151                         return -EINVAL;
 152                 }
 153
 154                 if (page_seen & (1 << page)) {
 155                         dev_err(dev, "Infinite loop in page redirection\n");
 156                         return -EINVAL;
 157                 }
 158
 159                 page_seen |= (1 << page);
 160         } while (1);
 161
 162         return page;
 163 }
 164
 165 static int ds2502_read_buf(struct udevice *dev, unsigned int offset,
 166                            u8 *buf, unsigned int count)
 167 {
 168         unsigned int min_page = offset / DS2502_PAGE_SIZE;
 169         unsigned int max_page = (offset + count - 1) / DS2502_PAGE_SIZE;
 170         int xfered = 0;
 171         u8 status_bytes[DS2502_STATUS_SIZE];
 172         int i;
 173         int ret;
 174
 175         if (min_page >= DS2502_PAGE_COUNT || max_page >= DS2502_PAGE_COUNT)
 176                 return -EINVAL;
 177
 178         if (min_page == 0 && max_page == 0) {
 179                 ret = ds2502_read_status_bytes(dev, status_bytes);
 180                 if (ret)
 181                         return ret;
 182         } else {
 183                 /* Dummy one to one page redirection */
 184                 memset(status_bytes, 0xff, sizeof(status_bytes));
 185         }
 186
 187         for (i = min_page; i <= max_page; i++) {
 188                 int page;
 189                 int pos;
 190                 int bytes_in_page;
 191                 int bytes_for_user;
 192
 193                 page = ds2502_indirect_page(dev, status_bytes, i);
 194                 if (page < 0)
 195                         return page;
 196                 dev_dbg(dev, "page logical %d => physical %d\n", i, page);
 197
 198                 pos = page * DS2502_PAGE_SIZE;
 199                 if (i == min_page)
 200                         pos += offset % DS2502_PAGE_SIZE;
 201
 202                 bytes_in_page = DS2502_PAGE_SIZE - (pos % DS2502_PAGE_SIZE);
 203
 204                 if (i == max_page)
 205                         bytes_for_user = count - xfered;
 206                 else
 207                         bytes_for_user = bytes_in_page;
 208
 209                 ret = ds2502_read(dev, DS2502_CMD_READ_GEN_CRC,
 210                                   bytes_in_page, pos,
 211                                   &buf[xfered], bytes_for_user);
 212                 if (ret < 0)
 213                         return ret;
 214
 215                 xfered += bytes_for_user;
 216         }
 217
 218         return 0;
 219 }
 220
 221 static int ds2502_probe(struct udevice *dev)
 222 {
 223         struct w1_device *w1;
 224
 225         w1 = dev_get_parent_plat(dev);
 226         w1->id = 0;
 227         return 0;
 228 }
 229
 230 static const struct w1_eeprom_ops ds2502_ops = {
 231         .read_buf       = ds2502_read_buf,
 232 };
 233
 234 static const struct udevice_id ds2502_id[] = {
 235         { .compatible = "maxim,ds2502", .data = W1_FAMILY_DS2502 },
 236         { },
 237 };
 238
 239 U_BOOT_DRIVER(ds2502) = {
 240         .name           = "ds2502",
 241         .id             = UCLASS_W1_EEPROM,
 242         .of_match       = ds2502_id,
 243         .ops            = &ds2502_ops,
 244         .probe          = ds2502_probe,
 245 };