drivers/misc/eeprom/ee1004.c - linux/torvalds/linux - Git at Google

 // 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;

 	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,
 };

 static int __init ee1004_init(void)
 {
 	return i2c_add_driver(&ee1004_driver);
 }
 module_init(ee1004_init);

 static void __exit ee1004_exit(void)
 {
 	i2c_del_driver(&ee1004_driver);
 }
 module_exit(ee1004_exit);

 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
 MODULE_AUTHOR("Jean Delvare");
 MODULE_LICENSE("GPL");
	// 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;

	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,
	};

	static int __init ee1004_init(void)
	{
	return i2c_add_driver(&ee1004_driver);
	}
	module_init(ee1004_init);

	static void __exit ee1004_exit(void)
	{
	i2c_del_driver(&ee1004_driver);
	}
	module_exit(ee1004_exit);

	MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs");
	MODULE_AUTHOR("Jean Delvare");
	MODULE_LICENSE("GPL");