diff options
Diffstat (limited to 'drivers/misc/eeprom/ee1004.c')
| -rw-r--r-- | drivers/misc/eeprom/ee1004.c | 245 |
1 files changed, 245 insertions, 0 deletions
diff --git a/drivers/misc/eeprom/ee1004.c b/drivers/misc/eeprom/ee1004.c new file mode 100644 index 000000000..c8c6deb7e --- /dev/null +++ b/drivers/misc/eeprom/ee1004.c @@ -0,0 +1,245 @@ +// 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_NUM_PAGES 2 +#define EE1004_PAGE_SIZE 256 +#define EE1004_PAGE_SHIFT 8 +#define EE1004_EEPROM_SIZE (EE1004_PAGE_SIZE * EE1004_NUM_PAGES) + +/* + * 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[EE1004_NUM_PAGES]; +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 int ee1004_set_current_page(struct device *dev, int page) +{ + int ret; + + if (page == ee1004_current_page) + return 0; + + /* Data is ignored */ + ret = i2c_smbus_write_byte(ee1004_set_page[page], 0x00); + /* + * 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 (ret == -ENXIO && ee1004_get_current_page() == page) + ret = 0; + if (ret < 0) { + dev_err(dev, "Failed to select page %d (%d)\n", page, ret); + return ret; + } + + dev_dbg(dev, "Selected page %d\n", page); + ee1004_current_page = page; + + return 0; +} + +static ssize_t ee1004_eeprom_read(struct i2c_client *client, char *buf, + unsigned int offset, size_t count) +{ + int status, page; + + page = offset >> EE1004_PAGE_SHIFT; + offset &= (1 << EE1004_PAGE_SHIFT) - 1; + + status = ee1004_set_current_page(&client->dev, page); + if (status) + return status; + + /* Can't cross page boundaries */ + if (offset + count > EE1004_PAGE_SIZE) + count = EE1004_PAGE_SIZE - offset; + + if (count > I2C_SMBUS_BLOCK_MAX) + count = I2C_SMBUS_BLOCK_MAX; + + return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf); +} + +static ssize_t eeprom_read(struct file *filp, struct kobject *kobj, + struct bin_attribute *bin_attr, + char *buf, loff_t off, size_t count) +{ + struct i2c_client *client = kobj_to_i2c_client(kobj); + size_t requested = count; + int ret = 0; + + /* + * Read data from chip, protecting against concurrent access to + * other EE1004 SPD EEPROMs on the same adapter. + */ + mutex_lock(&ee1004_bus_lock); + + while (count) { + ret = ee1004_eeprom_read(client, buf, off, count); + if (ret < 0) + goto out; + + buf += ret; + off += ret; + count -= ret; + } +out: + mutex_unlock(&ee1004_bus_lock); + + return ret < 0 ? ret : requested; +} + +static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE); + +static struct bin_attribute *ee1004_attrs[] = { + &bin_attr_eeprom, + NULL +}; + +BIN_ATTRIBUTE_GROUPS(ee1004); + +static void ee1004_cleanup(int idx) +{ + if (--ee1004_dev_count == 0) + while (--idx >= 0) { + i2c_unregister_device(ee1004_set_page[idx]); + ee1004_set_page[idx] = NULL; + } +} + +static int ee1004_probe(struct i2c_client *client) +{ + int err, cnr = 0; + + /* Make sure we can operate on this adapter */ + if (!i2c_check_functionality(client->adapter, + I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) && + !i2c_check_functionality(client->adapter, + I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA)) + return -EPFNOSUPPORT; + + /* Use 2 dummy devices for page select command */ + mutex_lock(&ee1004_bus_lock); + if (++ee1004_dev_count == 1) { + for (cnr = 0; cnr < EE1004_NUM_PAGES; cnr++) { + struct i2c_client *cl; + + cl = i2c_new_dummy_device(client->adapter, EE1004_ADDR_SET_PAGE + cnr); + if (IS_ERR(cl)) { + err = PTR_ERR(cl); + goto err_clients; + } + ee1004_set_page[cnr] = cl; + } + + /* Remember current page to avoid unneeded page select */ + err = ee1004_get_current_page(); + if (err < 0) + goto err_clients; + dev_dbg(&client->dev, "Currently selected page: %d\n", err); + ee1004_current_page = err; + } else if (client->adapter != ee1004_set_page[0]->adapter) { + dev_err(&client->dev, + "Driver only supports devices on a single I2C bus\n"); + err = -EOPNOTSUPP; + goto err_clients; + } + mutex_unlock(&ee1004_bus_lock); + + dev_info(&client->dev, + "%u byte EE1004-compliant SPD EEPROM, read-only\n", + EE1004_EEPROM_SIZE); + + return 0; + + err_clients: + ee1004_cleanup(cnr); + mutex_unlock(&ee1004_bus_lock); + + return err; +} + +static void ee1004_remove(struct i2c_client *client) +{ + /* Remove page select clients if this is the last device */ + mutex_lock(&ee1004_bus_lock); + ee1004_cleanup(EE1004_NUM_PAGES); + mutex_unlock(&ee1004_bus_lock); +} + +/*-------------------------------------------------------------------------*/ + +static struct i2c_driver ee1004_driver = { + .driver = { + .name = "ee1004", + .dev_groups = ee1004_groups, + }, + .probe_new = 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"); |