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- // SPDX-License-Identifier: GPL-2.0-or-later
- /*
- * ee1004 - driver for DDR4 SPD EEPROMs
- *
- * Copyright (C) 2017-2019 Jean Delvare
- *
- * Based on the at24 driver:
- * Copyright (C) 2005-2007 David Brownell
- * Copyright (C) 2008 Wolfram Sang, Pengutronix
- */
- #include <linux/i2c.h>
- #include <linux/init.h>
- #include <linux/kernel.h>
- #include <linux/mod_devicetable.h>
- #include <linux/module.h>
- #include <linux/mutex.h>
- /*
- * DDR4 memory modules use special EEPROMs following the Jedec EE1004
- * specification. These are 512-byte EEPROMs using a single I2C address
- * in the 0x50-0x57 range for data. One of two 256-byte page is selected
- * by writing a command to I2C address 0x36 or 0x37 on the same I2C bus.
- *
- * Therefore we need to request these 2 additional addresses, and serialize
- * access to all such EEPROMs with a single mutex.
- *
- * We assume it is safe to read up to 32 bytes at once from these EEPROMs.
- * We use SMBus access even if I2C is available, these EEPROMs are small
- * enough, and reading from them infrequent enough, that we favor simplicity
- * over performance.
- */
- #define EE1004_ADDR_SET_PAGE 0x36
- #define EE1004_EEPROM_SIZE 512
- #define EE1004_PAGE_SIZE 256
- #define EE1004_PAGE_SHIFT 8
- /*
- * Mutex protects ee1004_set_page and ee1004_dev_count, and must be held
- * from page selection to end of read.
- */
- static DEFINE_MUTEX(ee1004_bus_lock);
- static struct i2c_client *ee1004_set_page[2];
- static unsigned int ee1004_dev_count;
- static int ee1004_current_page;
- static const struct i2c_device_id ee1004_ids[] = {
- { "ee1004", 0 },
- { }
- };
- MODULE_DEVICE_TABLE(i2c, ee1004_ids);
- /*-------------------------------------------------------------------------*/
- static int ee1004_get_current_page(void)
- {
- int err;
- err = i2c_smbus_read_byte(ee1004_set_page[0]);
- if (err == -ENXIO) {
- /* Nack means page 1 is selected */
- return 1;
- }
- if (err < 0) {
- /* Anything else is a real error, bail out */
- return err;
- }
- /* Ack means page 0 is selected, returned value meaningless */
- return 0;
- }
- static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf,
- unsigned int offset, size_t count)
- {
- int status;
- if (count > I2C_SMBUS_BLOCK_MAX)
- count = I2C_SMBUS_BLOCK_MAX;
- /* Can't cross page boundaries */
- if (unlikely(offset + count > EE1004_PAGE_SIZE))
- count = EE1004_PAGE_SIZE - offset;
- if (count > I2C_SMBUS_BLOCK_MAX)
- count = I2C_SMBUS_BLOCK_MAX;
- status = i2c_smbus_read_i2c_block_data_or_emulated(client, offset,
- count, buf);
- dev_dbg(&client->dev, "read %zu@%d --> %d\n", count, offset, status);
- return status;
- }
- static ssize_t ee1004_read(struct file *filp, struct kobject *kobj,
- struct bin_attribute *bin_attr,
- char *buf, loff_t off, size_t count)
- {
- struct device *dev = kobj_to_dev(kobj);
- struct i2c_client *client = to_i2c_client(dev);
- size_t requested = count;
- int page;
- if (unlikely(!count))
- return count;
- page = off >> EE1004_PAGE_SHIFT;
- if (unlikely(page > 1))
- return 0;
- off &= (1 << EE1004_PAGE_SHIFT) - 1;
- /*
- * Read data from chip, protecting against concurrent access to
- * other EE1004 SPD EEPROMs on the same adapter.
- */
- mutex_lock(&ee1004_bus_lock);
- while (count) {
- int status;
- /* Select page */
- if (page != ee1004_current_page) {
- /* Data is ignored */
- status = i2c_smbus_write_byte(ee1004_set_page[page],
- 0x00);
- if (status == -ENXIO) {
- /*
- * Don't give up just yet. Some memory
- * modules will select the page but not
- * ack the command. Check which page is
- * selected now.
- */
- if (ee1004_get_current_page() == page)
- status = 0;
- }
- if (status < 0) {
- dev_err(dev, "Failed to select page %d (%d)\n",
- page, status);
- mutex_unlock(&ee1004_bus_lock);
- return status;
- }
- dev_dbg(dev, "Selected page %d\n", page);
- ee1004_current_page = page;
- }
- status = ee1004_eeprom_read(client, buf, off, count);
- if (status < 0) {
- mutex_unlock(&ee1004_bus_lock);
- return status;
- }
- buf += status;
- off += status;
- count -= status;
- if (off == EE1004_PAGE_SIZE) {
- page++;
- off = 0;
- }
- }
- mutex_unlock(&ee1004_bus_lock);
- return requested;
- }
- static const struct bin_attribute eeprom_attr = {
- .attr = {
- .name = "eeprom",
- .mode = 0444,
- },
- .size = EE1004_EEPROM_SIZE,
- .read = ee1004_read,
- };
- static int ee1004_probe(struct i2c_client *client,
- const struct i2c_device_id *id)
- {
- int err, cnr = 0;
- const char *slow = NULL;
- /* Make sure we can operate on this adapter */
- if (!i2c_check_functionality(client->adapter,
- I2C_FUNC_SMBUS_READ_BYTE |
- I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
- if (i2c_check_functionality(client->adapter,
- I2C_FUNC_SMBUS_READ_BYTE |
- I2C_FUNC_SMBUS_READ_WORD_DATA))
- slow = "word";
- else if (i2c_check_functionality(client->adapter,
- I2C_FUNC_SMBUS_READ_BYTE |
- I2C_FUNC_SMBUS_READ_BYTE_DATA))
- slow = "byte";
- else
- return -EPFNOSUPPORT;
- }
- /* Use 2 dummy devices for page select command */
- mutex_lock(&ee1004_bus_lock);
- if (++ee1004_dev_count == 1) {
- for (cnr = 0; cnr < 2; cnr++) {
- ee1004_set_page[cnr] = i2c_new_dummy_device(client->adapter,
- EE1004_ADDR_SET_PAGE + cnr);
- if (IS_ERR(ee1004_set_page[cnr])) {
- dev_err(&client->dev,
- "address 0x%02x unavailable\n",
- EE1004_ADDR_SET_PAGE + cnr);
- err = PTR_ERR(ee1004_set_page[cnr]);
- goto err_clients;
- }
- }
- } else if (i2c_adapter_id(client->adapter) !=
- i2c_adapter_id(ee1004_set_page[0]->adapter)) {
- dev_err(&client->dev,
- "Driver only supports devices on a single I2C bus\n");
- err = -EOPNOTSUPP;
- goto err_clients;
- }
- /* Remember current page to avoid unneeded page select */
- err = ee1004_get_current_page();
- if (err < 0)
- goto err_clients;
- ee1004_current_page = err;
- dev_dbg(&client->dev, "Currently selected page: %d\n",
- ee1004_current_page);
- mutex_unlock(&ee1004_bus_lock);
- /* Create the sysfs eeprom file */
- err = sysfs_create_bin_file(&client->dev.kobj, &eeprom_attr);
- if (err)
- goto err_clients_lock;
- dev_info(&client->dev,
- "%u byte EE1004-compliant SPD EEPROM, read-only\n",
- EE1004_EEPROM_SIZE);
- if (slow)
- dev_notice(&client->dev,
- "Falling back to %s reads, performance will suffer\n",
- slow);
- return 0;
- err_clients_lock:
- mutex_lock(&ee1004_bus_lock);
- err_clients:
- if (--ee1004_dev_count == 0) {
- for (cnr--; cnr >= 0; cnr--) {
- i2c_unregister_device(ee1004_set_page[cnr]);
- ee1004_set_page[cnr] = NULL;
- }
- }
- mutex_unlock(&ee1004_bus_lock);
- return err;
- }
- static int ee1004_remove(struct i2c_client *client)
- {
- int i;
- sysfs_remove_bin_file(&client->dev.kobj, &eeprom_attr);
- /* Remove page select clients if this is the last device */
- mutex_lock(&ee1004_bus_lock);
- if (--ee1004_dev_count == 0) {
- for (i = 0; i < 2; i++) {
- i2c_unregister_device(ee1004_set_page[i]);
- ee1004_set_page[i] = NULL;
- }
- }
- mutex_unlock(&ee1004_bus_lock);
- return 0;
- }
- /*-------------------------------------------------------------------------*/
- static struct i2c_driver ee1004_driver = {
- .driver = {
- .name = "ee1004",
- },
- .probe = ee1004_probe,
- .remove = ee1004_remove,
- .id_table = ee1004_ids,
- };
- module_i2c_driver(ee1004_driver);
- MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
- MODULE_AUTHOR("Jean Delvare");
- MODULE_LICENSE("GPL");
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