drivers/misc/eeprom/ee1004.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * ee1004 - driver for DDR4 SPD EEPROMs
   4  *
   5  * Copyright (C) 2017-2019 Jean Delvare
   6  *
   7  * Based on the at24 driver:
   8  * Copyright (C) 2005-2007 David Brownell
   9  * Copyright (C) 2008 Wolfram Sang, Pengutronix
  10  */
  11
  12 #include <linux/device.h>
  13 #include <linux/i2c.h>
  14 #include <linux/init.h>
  15 #include <linux/kernel.h>
  16 #include <linux/mod_devicetable.h>
  17 #include <linux/module.h>
  18 #include <linux/mutex.h>
  19 #include <linux/nvmem-provider.h>
  20
  21 /*
  22  * DDR4 memory modules use special EEPROMs following the Jedec EE1004
  23  * specification. These are 512-byte EEPROMs using a single I2C address
  24  * in the 0x50-0x57 range for data. One of two 256-byte page is selected
  25  * by writing a command to I2C address 0x36 or 0x37 on the same I2C bus.
  26  *
  27  * Therefore we need to request these 2 additional addresses, and serialize
  28  * access to all such EEPROMs with a single mutex.
  29  *
  30  * We assume it is safe to read up to 32 bytes at once from these EEPROMs.
  31  * We use SMBus access even if I2C is available, these EEPROMs are small
  32  * enough, and reading from them infrequent enough, that we favor simplicity
  33  * over performance.
  34  */
  35
  36 #define EE1004_MAX_BUSSES               8
  37 #define EE1004_ADDR_SET_PAGE            0x36
  38 #define EE1004_NUM_PAGES                2
  39 #define EE1004_PAGE_SIZE                256
  40 #define EE1004_PAGE_SHIFT               8
  41 #define EE1004_EEPROM_SIZE              (EE1004_PAGE_SIZE * EE1004_NUM_PAGES)
  42
  43 /*
  44  * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
  45  * from page selection to end of read.
  46  */
  47 static DEFINE_MUTEX(ee1004_bus_lock);
  48
  49 static struct ee1004_bus_data {
  50         struct i2c_adapter *adap;
  51         struct i2c_client *set_page[EE1004_NUM_PAGES];
  52         unsigned int dev_count;
  53         int current_page;
  54 } ee1004_bus_data[EE1004_MAX_BUSSES];
  55
  56 static const struct i2c_device_id ee1004_ids[] = {
  57         { "ee1004" },
  58         { }
  59 };
  60 MODULE_DEVICE_TABLE(i2c, ee1004_ids);
  61
  62 /*-------------------------------------------------------------------------*/
  63
  64 static struct ee1004_bus_data *ee1004_get_bus_data(struct i2c_adapter *adap)
  65 {
  66         int i;
  67
  68         for (i = 0; i < EE1004_MAX_BUSSES; i++)
  69                 if (ee1004_bus_data[i].adap == adap)
  70                         return ee1004_bus_data + i;
  71
  72         /* If not existent yet, create new entry */
  73         for (i = 0; i < EE1004_MAX_BUSSES; i++)
  74                 if (!ee1004_bus_data[i].adap) {
  75                         ee1004_bus_data[i].adap = adap;
  76                         return ee1004_bus_data + i;
  77                 }
  78
  79         return NULL;
  80 }
  81
  82 static int ee1004_get_current_page(struct ee1004_bus_data *bd)
  83 {
  84         int err;
  85
  86         err = i2c_smbus_read_byte(bd->set_page[0]);
  87         if (err == -ENXIO) {
  88                 /* Nack means page 1 is selected */
  89                 return 1;
  90         }
  91         if (err < 0) {
  92                 /* Anything else is a real error, bail out */
  93                 return err;
  94         }
  95
  96         /* Ack means page 0 is selected, returned value meaningless */
  97         return 0;
  98 }
  99
 100 static int ee1004_set_current_page(struct i2c_client *client, int page)
 101 {
 102         struct ee1004_bus_data *bd = i2c_get_clientdata(client);
 103         int ret;
 104
 105         if (page == bd->current_page)
 106                 return 0;
 107
 108         /* Data is ignored */
 109         ret = i2c_smbus_write_byte(bd->set_page[page], 0x00);
 110         /*
 111          * Don't give up just yet. Some memory modules will select the page
 112          * but not ack the command. Check which page is selected now.
 113          */
 114         if (ret == -ENXIO && ee1004_get_current_page(bd) == page)
 115                 ret = 0;
 116         if (ret < 0) {
 117                 dev_err(&client->dev, "Failed to select page %d (%d)\n", page, ret);
 118                 return ret;
 119         }
 120
 121         dev_dbg(&client->dev, "Selected page %d\n", page);
 122         bd->current_page = page;
 123
 124         return 0;
 125 }
 126
 127 static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
 128                                   unsigned int offset, size_t count)
 129 {
 130         int status, page;
 131
 132         page = offset >> EE1004_PAGE_SHIFT;
 133         offset &= (1 << EE1004_PAGE_SHIFT) - 1;
 134
 135         status = ee1004_set_current_page(client, page);
 136         if (status)
 137                 return status;
 138
 139         /* Can't cross page boundaries */
 140         if (offset + count > EE1004_PAGE_SIZE)
 141                 count = EE1004_PAGE_SIZE - offset;
 142
 143         if (count > I2C_SMBUS_BLOCK_MAX)
 144                 count = I2C_SMBUS_BLOCK_MAX;
 145
 146         return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf);
 147 }
 148
 149 static int ee1004_read(void *priv, unsigned int off, void *val, size_t count)
 150 {
 151         struct i2c_client *client = priv;
 152         char *buf = val;
 153         int ret;
 154
 155         if (unlikely(!count))
 156                 return count;
 157
 158         if (off + count > EE1004_EEPROM_SIZE)
 159                 return -EINVAL;
 160
 161         /*
 162          * Read data from chip, protecting against concurrent access to
 163          * other EE1004 SPD EEPROMs on the same adapter.
 164          */
 165         mutex_lock(&ee1004_bus_lock);
 166
 167         while (count) {
 168                 ret = ee1004_eeprom_read(client, buf, off, count);
 169                 if (ret < 0) {
 170                         mutex_unlock(&ee1004_bus_lock);
 171                         return ret;
 172                 }
 173
 174                 buf += ret;
 175                 off += ret;
 176                 count -= ret;
 177         }
 178
 179         mutex_unlock(&ee1004_bus_lock);
 180
 181         return 0;
 182 }
 183
 184 static void ee1004_probe_temp_sensor(struct i2c_client *client)
 185 {
 186         struct i2c_board_info info = { .type = "jc42" };
 187         unsigned short addr = 0x18 | (client->addr & 7);
 188         unsigned short addr_list[] = { addr, I2C_CLIENT_END };
 189         u8 data[2];
 190         int ret;
 191
 192         /* byte 14, bit 7 is set if temp sensor is present */
 193         ret = ee1004_eeprom_read(client, data, 14, 1);
 194         if (ret != 1)
 195                 return;
 196
 197         if (!(data[0] & BIT(7))) {
 198                 /*
 199                  * If the SPD data suggests that there is no temperature
 200                  * sensor, it may still be there for SPD revision 1.0.
 201                  * See SPD Annex L, Revision 1 and 2, for details.
 202                  * Check DIMM type and SPD revision; if it is a DDR4
 203                  * with SPD revision 1.0, check the thermal sensor address
 204                  * and instantiate the jc42 driver if a chip is found at
 205                  * that address.
 206                  * It is not necessary to check if there is a chip at the
 207                  * temperature sensor address since i2c_new_scanned_device()
 208                  * will do that and return silently if no chip is found.
 209                  */
 210                 ret = ee1004_eeprom_read(client, data, 1, 2);
 211                 if (ret != 2 || data[0] != 0x10 || data[1] != 0x0c)
 212                         return;
 213         }
 214         i2c_new_scanned_device(client->adapter, &info, addr_list, NULL);
 215 }
 216
 217 static void ee1004_cleanup(int idx, struct ee1004_bus_data *bd)
 218 {
 219         if (--bd->dev_count == 0) {
 220                 while (--idx >= 0)
 221                         i2c_unregister_device(bd->set_page[idx]);
 222                 memset(bd, 0, sizeof(struct ee1004_bus_data));
 223         }
 224 }
 225
 226 static void ee1004_cleanup_bus_data(void *data)
 227 {
 228         struct ee1004_bus_data *bd = data;
 229
 230         /* Remove page select clients if this is the last device */
 231         mutex_lock(&ee1004_bus_lock);
 232         ee1004_cleanup(EE1004_NUM_PAGES, bd);
 233         mutex_unlock(&ee1004_bus_lock);
 234 }
 235
 236 static int ee1004_init_bus_data(struct i2c_client *client)
 237 {
 238         struct ee1004_bus_data *bd;
 239         int err, cnr = 0;
 240
 241         bd = ee1004_get_bus_data(client->adapter);
 242         if (!bd)
 243                 return dev_err_probe(&client->dev, -ENOSPC, "Only %d busses supported",
 244                                      EE1004_MAX_BUSSES);
 245
 246         i2c_set_clientdata(client, bd);
 247
 248         if (++bd->dev_count == 1) {
 249                 /* Use 2 dummy devices for page select command */
 250                 for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) {
 251                         struct i2c_client *cl;
 252
 253                         cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr);
 254                         if (IS_ERR(cl)) {
 255                                 err = PTR_ERR(cl);
 256                                 goto err_out;
 257                         }
 258
 259                         bd->set_page[cnr] = cl;
 260                 }
 261
 262                 /* Remember current page to avoid unneeded page select */
 263                 err = ee1004_get_current_page(bd);
 264                 if (err < 0)
 265                         goto err_out;
 266
 267                 dev_dbg(&client->dev, "Currently selected page: %d\n", err);
 268                 bd->current_page = err;
 269         }
 270
 271         return 0;
 272
 273 err_out:
 274         ee1004_cleanup(cnr, bd);
 275
 276         return err;
 277 }
 278
 279 static int ee1004_probe(struct i2c_client *client)
 280 {
 281         struct nvmem_config config = {
 282                 .dev = &client->dev,
 283                 .name = dev_name(&client->dev),
 284                 .id = NVMEM_DEVID_NONE,
 285                 .owner = THIS_MODULE,
 286                 .type = NVMEM_TYPE_EEPROM,
 287                 .read_only = true,
 288                 .root_only = false,
 289                 .reg_read = ee1004_read,
 290                 .size = EE1004_EEPROM_SIZE,
 291                 .word_size = 1,
 292                 .stride = 1,
 293                 .priv = client,
 294                 .compat = true,
 295                 .base_dev = &client->dev,
 296         };
 297         struct nvmem_device *ndev;
 298         int err;
 299
 300         /* Make sure we can operate on this adapter */
 301         if (!i2c_check_functionality(client->adapter,
 302                                      I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) &&
 303             !i2c_check_functionality(client->adapter,
 304                                      I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA))
 305                 return -EPFNOSUPPORT;
 306
 307         mutex_lock(&ee1004_bus_lock);
 308
 309         err = ee1004_init_bus_data(client);
 310         if (err < 0) {
 311                 mutex_unlock(&ee1004_bus_lock);
 312                 return err;
 313         }
 314
 315         ee1004_probe_temp_sensor(client);
 316
 317         mutex_unlock(&ee1004_bus_lock);
 318
 319         err = devm_add_action_or_reset(&client->dev, ee1004_cleanup_bus_data,
 320                                        i2c_get_clientdata(client));
 321         if (err < 0)
 322                 return err;
 323
 324         ndev = devm_nvmem_register(&client->dev, &config);
 325         if (IS_ERR(ndev))
 326                 return PTR_ERR(ndev);
 327
 328         dev_info(&client->dev,
 329                  "%u byte EE1004-compliant SPD EEPROM, read-only\n",
 330                  EE1004_EEPROM_SIZE);
 331
 332         return 0;
 333 }
 334
 335 /*-------------------------------------------------------------------------*/
 336
 337 static struct i2c_driver ee1004_driver = {
 338         .driver = {
 339                 .name = "ee1004",
 340         },
 341         .probe = ee1004_probe,
 342         .id_table = ee1004_ids,
 343 };
 344 module_i2c_driver(ee1004_driver);
 345
 346 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
 347 MODULE_AUTHOR("Jean Delvare");
 348 MODULE_LICENSE("GPL");