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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_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;
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 int 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);
return 0;
}
/*-------------------------------------------------------------------------*/
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");
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