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/*
* 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;
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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