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/i2c.h>
  13 #include <linux/init.h>
  14 #include <linux/kernel.h>
  15 #include <linux/mod_devicetable.h>
  16 #include <linux/module.h>
  17 #include <linux/mutex.h>
  18
  19 /*
  20  * DDR4 memory modules use special EEPROMs following the Jedec EE1004
  21  * specification. These are 512-byte EEPROMs using a single I2C address
  22  * in the 0x50-0x57 range for data. One of two 256-byte page is selected
  23  * by writing a command to I2C address 0x36 or 0x37 on the same I2C bus.
  24  *
  25  * Therefore we need to request these 2 additional addresses, and serialize
  26  * access to all such EEPROMs with a single mutex.
  27  *
  28  * We assume it is safe to read up to 32 bytes at once from these EEPROMs.
  29  * We use SMBus access even if I2C is available, these EEPROMs are small
  30  * enough, and reading from them infrequent enough, that we favor simplicity
  31  * over performance.
  32  */
  33
  34 #define EE1004_ADDR_SET_PAGE            0x36
  35 #define EE1004_EEPROM_SIZE              512
  36 #define EE1004_PAGE_SIZE                256
  37 #define EE1004_PAGE_SHIFT               8
  38
  39 /*
  40  * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
  41  * from page selection to end of read.
  42  */
  43 static DEFINE_MUTEX(ee1004_bus_lock);
  44 static struct i2c_client *ee1004_set_page[2];
  45 static unsigned int ee1004_dev_count;
  46 static int ee1004_current_page;
  47
  48 static const struct i2c_device_id ee1004_ids[] = {
  49         { "ee1004", 0 },
  50         { }
  51 };
  52 MODULE_DEVICE_TABLE(i2c, ee1004_ids);
  53
  54 /*-------------------------------------------------------------------------*/
  55
  56 static int ee1004_get_current_page(void)
  57 {
  58         int err;
  59
  60         err = i2c_smbus_read_byte(ee1004_set_page[0]);
  61         if (err == -ENXIO) {
  62                 /* Nack means page 1 is selected */
  63                 return 1;
  64         }
  65         if (err < 0) {
  66                 /* Anything else is a real error, bail out */
  67                 return err;
  68         }
  69
  70         /* Ack means page 0 is selected, returned value meaningless */
  71         return 0;
  72 }
  73
  74 static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
  75                                   unsigned int offset, size_t count)
  76 {
  77         int status;
  78
  79         if (count > I2C_SMBUS_BLOCK_MAX)
  80                 count = I2C_SMBUS_BLOCK_MAX;
  81         /* Can't cross page boundaries */
  82         if (unlikely(offset + count > EE1004_PAGE_SIZE))
  83                 count = EE1004_PAGE_SIZE - offset;
  84
  85         if (count > I2C_SMBUS_BLOCK_MAX)
  86                 count = I2C_SMBUS_BLOCK_MAX;
  87
  88         status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset,
  89                                                            count, buf);
  90         dev_dbg(&client->dev, "read %zu@%d --> %d\n", count, offset, status);
  91
  92         return status;
  93 }
  94
  95 static ssize_t ee1004_read(struct file *filp, struct kobject *kobj,
  96                            struct bin_attribute *bin_attr,
  97                            char *buf, loff_t off, size_t count)
  98 {
  99         struct device *dev = kobj_to_dev(kobj);
 100         struct i2c_client *client = to_i2c_client(dev);
 101         size_t requested = count;
 102         int page;
 103
 104         if (unlikely(!count))
 105                 return count;
 106
 107         page = off >> EE1004_PAGE_SHIFT;
 108         if (unlikely(page > 1))
 109                 return 0;
 110         off &= (1 << EE1004_PAGE_SHIFT) - 1;
 111
 112         /*
 113          * Read data from chip, protecting against concurrent access to
 114          * other EE1004 SPD EEPROMs on the same adapter.
 115          */
 116         mutex_lock(&ee1004_bus_lock);
 117
 118         while (count) {
 119                 int status;
 120
 121                 /* Select page */
 122                 if (page != ee1004_current_page) {
 123                         /* Data is ignored */
 124                         status = i2c_smbus_write_byte(ee1004_set_page[page],
 125                                                       0x00);
 126                         if (status == -ENXIO) {
 127                                 /*
 128                                  * Don't give up just yet. Some memory
 129                                  * modules will select the page but not
 130                                  * ack the command. Check which page is
 131                                  * selected now.
 132                                  */
 133                                 if (ee1004_get_current_page() == page)
 134                                         status = 0;
 135                         }
 136                         if (status < 0) {
 137                                 dev_err(dev, "Failed to select page %d (%d)\n",
 138                                         page, status);
 139                                 mutex_unlock(&ee1004_bus_lock);
 140                                 return status;
 141                         }
 142                         dev_dbg(dev, "Selected page %d\n", page);
 143                         ee1004_current_page = page;
 144                 }
 145
 146                 status = ee1004_eeprom_read(client, buf, off, count);
 147                 if (status < 0) {
 148                         mutex_unlock(&ee1004_bus_lock);
 149                         return status;
 150                 }
 151                 buf += status;
 152                 off += status;
 153                 count -= status;
 154
 155                 if (off == EE1004_PAGE_SIZE) {
 156                         page++;
 157                         off = 0;
 158                 }
 159         }
 160
 161         mutex_unlock(&ee1004_bus_lock);
 162
 163         return requested;
 164 }
 165
 166 static const struct bin_attribute eeprom_attr = {
 167         .attr = {
 168                 .name = "eeprom",
 169                 .mode = 0444,
 170         },
 171         .size = EE1004_EEPROM_SIZE,
 172         .read = ee1004_read,
 173 };
 174
 175 static int ee1004_probe(struct i2c_client *client,
 176                         const struct i2c_device_id *id)
 177 {
 178         int err, cnr = 0;
 179         const char *slow = NULL;
 180
 181         /* Make sure we can operate on this adapter */
 182         if (!i2c_check_functionality(client->adapter,
 183                                      I2C_FUNC_SMBUS_READ_BYTE |
 184                                      I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
 185                 if (i2c_check_functionality(client->adapter,
 186                                      I2C_FUNC_SMBUS_READ_BYTE |
 187                                      I2C_FUNC_SMBUS_READ_WORD_DATA))
 188                         slow = "word";
 189                 else if (i2c_check_functionality(client->adapter,
 190                                      I2C_FUNC_SMBUS_READ_BYTE |
 191                                      I2C_FUNC_SMBUS_READ_BYTE_DATA))
 192                         slow = "byte";
 193                 else
 194                         return -EPFNOSUPPORT;
 195         }
 196
 197         /* Use 2 dummy devices for page select command */
 198         mutex_lock(&ee1004_bus_lock);
 199         if (++ee1004_dev_count == 1) {
 200                 for (cnr = 0; cnr < 2; cnr++) {
 201                         ee1004_set_page[cnr] = i2c_new_dummy_device(client->adapter,
 202                                                 EE1004_ADDR_SET_PAGE + cnr);
 203                         if (IS_ERR(ee1004_set_page[cnr])) {
 204                                 dev_err(&client->dev,
 205                                         "address 0x%02x unavailable\n",
 206                                         EE1004_ADDR_SET_PAGE + cnr);
 207                                 err = PTR_ERR(ee1004_set_page[cnr]);
 208                                 goto err_clients;
 209                         }
 210                 }
 211         } else if (i2c_adapter_id(client->adapter) !=
 212                    i2c_adapter_id(ee1004_set_page[0]->adapter)) {
 213                 dev_err(&client->dev,
 214                         "Driver only supports devices on a single I2C bus\n");
 215                 err = -EOPNOTSUPP;
 216                 goto err_clients;
 217         }
 218
 219         /* Remember current page to avoid unneeded page select */
 220         err = ee1004_get_current_page();
 221         if (err < 0)
 222                 goto err_clients;
 223         ee1004_current_page = err;
 224         dev_dbg(&client->dev, "Currently selected page: %d\n",
 225                 ee1004_current_page);
 226         mutex_unlock(&ee1004_bus_lock);
 227
 228         /* Create the sysfs eeprom file */
 229         err = sysfs_create_bin_file(&client->dev.kobj, &eeprom_attr);
 230         if (err)
 231                 goto err_clients_lock;
 232
 233         dev_info(&client->dev,
 234                  "%u byte EE1004-compliant SPD EEPROM, read-only\n",
 235                  EE1004_EEPROM_SIZE);
 236         if (slow)
 237                 dev_notice(&client->dev,
 238                            "Falling back to %s reads, performance will suffer\n",
 239                            slow);
 240
 241         return 0;
 242
 243  err_clients_lock:
 244         mutex_lock(&ee1004_bus_lock);
 245  err_clients:
 246         if (--ee1004_dev_count == 0) {
 247                 for (cnr--; cnr >= 0; cnr--) {
 248                         i2c_unregister_device(ee1004_set_page[cnr]);
 249                         ee1004_set_page[cnr] = NULL;
 250                 }
 251         }
 252         mutex_unlock(&ee1004_bus_lock);
 253
 254         return err;
 255 }
 256
 257 static int ee1004_remove(struct i2c_client *client)
 258 {
 259         int i;
 260
 261         sysfs_remove_bin_file(&client->dev.kobj, &eeprom_attr);
 262
 263         /* Remove page select clients if this is the last device */
 264         mutex_lock(&ee1004_bus_lock);
 265         if (--ee1004_dev_count == 0) {
 266                 for (i = 0; i < 2; i++) {
 267                         i2c_unregister_device(ee1004_set_page[i]);
 268                         ee1004_set_page[i] = NULL;
 269                 }
 270         }
 271         mutex_unlock(&ee1004_bus_lock);
 272
 273         return 0;
 274 }
 275
 276 /*-------------------------------------------------------------------------*/
 277
 278 static struct i2c_driver ee1004_driver = {
 279         .driver = {
 280                 .name = "ee1004",
 281         },
 282         .probe = ee1004_probe,
 283         .remove = ee1004_remove,
 284         .id_table = ee1004_ids,
 285 };
 286 module_i2c_driver(ee1004_driver);
 287
 288 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
 289 MODULE_AUTHOR("Jean Delvare");
 290 MODULE_LICENSE("GPL");