i2c: New-style EEPROM driver using device IDs

Add a new-style driver for most I2C EEPROMs, giving sysfs read/write
access to their data. Tested with various chips and clock rates.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

drivers/i2c/chips/Kconfig

@@ -14,6 +14,32 @@ config DS1682
 	  This driver can also be built as a module.  If so, the module
 	  will be called ds1682.
 
+config AT24
+	tristate "EEPROMs from most vendors"
+	depends on SYSFS && EXPERIMENTAL
+	help
+	  Enable this driver to get read/write support to most I2C EEPROMs,
+	  after you configure the driver to know about each EEPROM on
+	  your target board.  Use these generic chip names, instead of
+	  vendor-specific ones like at24c64 or 24lc02:
+
+	     24c00, 24c01, 24c02, spd (readonly 24c02), 24c04, 24c08,
+	     24c16, 24c32, 24c64, 24c128, 24c256, 24c512, 24c1024
+
+	  Unless you like data loss puzzles, always be sure that any chip
+	  you configure as a 24c32 (32 kbit) or larger is NOT really a
+	  24c16 (16 kbit) or smaller, and vice versa. Marking the chip
+	  as read-only won't help recover from this. Also, if your chip
+	  has any software write-protect mechanism you may want to review the
+	  code to make sure this driver won't turn it on by accident.
+
+	  If you use this with an SMBus adapter instead of an I2C adapter,
+	  full functionality is not available.  Only smaller devices are
+	  supported (24c16 and below, max 4 kByte).
+
+	  This driver can also be built as a module.  If so, the module
+	  will be called at24.
+
 config SENSORS_EEPROM
 	tristate "EEPROM reader"
 	depends on EXPERIMENTAL

drivers/i2c/chips/Makefile

@@ -10,6 +10,7 @@
 #
 
 obj-$(CONFIG_DS1682)		+= ds1682.o
+obj-$(CONFIG_AT24)		+= at24.o
 obj-$(CONFIG_SENSORS_EEPROM)	+= eeprom.o
 obj-$(CONFIG_SENSORS_MAX6875)	+= max6875.o
 obj-$(CONFIG_SENSORS_PCA9539)	+= pca9539.o

drivers/i2c/chips/at24.c

@@ -0,0 +1,583 @@
+/*
+ * at24.c - handle most I2C EEPROMs
+ *
+ * Copyright (C) 2005-2007 David Brownell
+ * Copyright (C) 2008 Wolfram Sang, Pengutronix
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/delay.h>
+#include <linux/mutex.h>
+#include <linux/sysfs.h>
+#include <linux/mod_devicetable.h>
+#include <linux/log2.h>
+#include <linux/bitops.h>
+#include <linux/jiffies.h>
+#include <linux/i2c.h>
+#include <linux/i2c/at24.h>
+
+/*
+ * I2C EEPROMs from most vendors are inexpensive and mostly interchangeable.
+ * Differences between different vendor product lines (like Atmel AT24C or
+ * MicroChip 24LC, etc) won't much matter for typical read/write access.
+ * There are also I2C RAM chips, likewise interchangeable. One example
+ * would be the PCF8570, which acts like a 24c02 EEPROM (256 bytes).
+ *
+ * However, misconfiguration can lose data. "Set 16-bit memory address"
+ * to a part with 8-bit addressing will overwrite data. Writing with too
+ * big a page size also loses data. And it's not safe to assume that the
+ * conventional addresses 0x50..0x57 only hold eeproms; a PCF8563 RTC
+ * uses 0x51, for just one example.
+ *
+ * Accordingly, explicit board-specific configuration data should be used
+ * in almost all cases. (One partial exception is an SMBus used to access
+ * "SPD" data for DRAM sticks. Those only use 24c02 EEPROMs.)
+ *
+ * So this driver uses "new style" I2C driver binding, expecting to be
+ * told what devices exist. That may be in arch/X/mach-Y/board-Z.c or
+ * similar kernel-resident tables; or, configuration data coming from
+ * a bootloader.
+ *
+ * Other than binding model, current differences from "eeprom" driver are
+ * that this one handles write access and isn't restricted to 24c02 devices.
+ * It also handles larger devices (32 kbit and up) with two-byte addresses,
+ * which won't work on pure SMBus systems.
+ */
+
+struct at24_data {
+	struct at24_platform_data chip;
+	bool use_smbus;
+
+	/*
+	 * Lock protects against activities from other Linux tasks,
+	 * but not from changes by other I2C masters.
+	 */
+	struct mutex lock;
+	struct bin_attribute bin;
+
+	u8 *writebuf;
+	unsigned write_max;
+	unsigned num_addresses;
+
+	/*
+	 * Some chips tie up multiple I2C addresses; dummy devices reserve
+	 * them for us, and we'll use them with SMBus calls.
+	 */
+	struct i2c_client *client[];
+};
+
+/*
+ * This parameter is to help this driver avoid blocking other drivers out
+ * of I2C for potentially troublesome amounts of time. With a 100 kHz I2C
+ * clock, one 256 byte read takes about 1/43 second which is excessive;
+ * but the 1/170 second it takes at 400 kHz may be quite reasonable; and
+ * at 1 MHz (Fm+) a 1/430 second delay could easily be invisible.
+ *
+ * This value is forced to be a power of two so that writes align on pages.
+ */
+static unsigned io_limit = 128;
+module_param(io_limit, uint, 0);
+MODULE_PARM_DESC(io_limit, "Maximum bytes per I/O (default 128)");
+
+/*
+ * Specs often allow 5 msec for a page write, sometimes 20 msec;
+ * it's important to recover from write timeouts.
+ */
+static unsigned write_timeout = 25;
+module_param(write_timeout, uint, 0);
+MODULE_PARM_DESC(write_timeout, "Time (in ms) to try writes (default 25)");
+
+#define AT24_SIZE_BYTELEN 5
+#define AT24_SIZE_FLAGS 8
+
+#define AT24_BITMASK(x) (BIT(x) - 1)
+
+/* create non-zero magic value for given eeprom parameters */
+#define AT24_DEVICE_MAGIC(_len, _flags) 		\
+	((1 << AT24_SIZE_FLAGS | (_flags)) 		\
+	    << AT24_SIZE_BYTELEN | ilog2(_len))
+
+static const struct i2c_device_id at24_ids[] = {
+	/* needs 8 addresses as A0-A2 are ignored */
+	{ "24c00", AT24_DEVICE_MAGIC(128 / 8, AT24_FLAG_TAKE8ADDR) },
+	/* old variants can't be handled with this generic entry! */
+	{ "24c01", AT24_DEVICE_MAGIC(1024 / 8, 0) },
+	{ "24c02", AT24_DEVICE_MAGIC(2048 / 8, 0) },
+	/* spd is a 24c02 in memory DIMMs */
+	{ "spd", AT24_DEVICE_MAGIC(2048 / 8,
+		AT24_FLAG_READONLY | AT24_FLAG_IRUGO) },
+	{ "24c04", AT24_DEVICE_MAGIC(4096 / 8, 0) },
+	/* 24rf08 quirk is handled at i2c-core */
+	{ "24c08", AT24_DEVICE_MAGIC(8192 / 8, 0) },
+	{ "24c16", AT24_DEVICE_MAGIC(16384 / 8, 0) },
+	{ "24c32", AT24_DEVICE_MAGIC(32768 / 8, AT24_FLAG_ADDR16) },
+	{ "24c64", AT24_DEVICE_MAGIC(65536 / 8, AT24_FLAG_ADDR16) },
+	{ "24c128", AT24_DEVICE_MAGIC(131072 / 8, AT24_FLAG_ADDR16) },
+	{ "24c256", AT24_DEVICE_MAGIC(262144 / 8, AT24_FLAG_ADDR16) },
+	{ "24c512", AT24_DEVICE_MAGIC(524288 / 8, AT24_FLAG_ADDR16) },
+	{ "24c1024", AT24_DEVICE_MAGIC(1048576 / 8, AT24_FLAG_ADDR16) },
+	{ "at24", 0 },
+	{ /* END OF LIST */ }
+};
+MODULE_DEVICE_TABLE(i2c, at24_ids);
+
+/*-------------------------------------------------------------------------*/
+
+/*
+ * This routine supports chips which consume multiple I2C addresses. It
+ * computes the addressing information to be used for a given r/w request.
+ * Assumes that sanity checks for offset happened at sysfs-layer.
+ */
+static struct i2c_client *at24_translate_offset(struct at24_data *at24,
+		unsigned *offset)
+{
+	unsigned i;
+
+	if (at24->chip.flags & AT24_FLAG_ADDR16) {
+		i = *offset >> 16;
+		*offset &= 0xffff;
+	} else {
+		i = *offset >> 8;
+		*offset &= 0xff;
+	}
+
+	return at24->client[i];
+}
+
+static ssize_t at24_eeprom_read(struct at24_data *at24, char *buf,
+		unsigned offset, size_t count)
+{
+	struct i2c_msg msg[2];
+	u8 msgbuf[2];
+	struct i2c_client *client;
+	int status, i;
+
+	memset(msg, 0, sizeof(msg));
+
+	/*
+	 * REVISIT some multi-address chips don't rollover page reads to
+	 * the next slave address, so we may need to truncate the count.
+	 * Those chips might need another quirk flag.
+	 *
+	 * If the real hardware used four adjacent 24c02 chips and that
+	 * were misconfigured as one 24c08, that would be a similar effect:
+	 * one "eeprom" file not four, but larger reads would fail when
+	 * they crossed certain pages.
+	 */
+
+	/*
+	 * Slave address and byte offset derive from the offset. Always
+	 * set the byte address; on a multi-master board, another master
+	 * may have changed the chip's "current" address pointer.
+	 */
+	client = at24_translate_offset(at24, &offset);
+
+	if (count > io_limit)
+		count = io_limit;
+
+	/* Smaller eeproms can work given some SMBus extension calls */
+	if (at24->use_smbus) {
+		if (count > I2C_SMBUS_BLOCK_MAX)
+			count = I2C_SMBUS_BLOCK_MAX;
+		status = i2c_smbus_read_i2c_block_data(client, offset,
+				count, buf);
+		dev_dbg(&client->dev, "smbus read %zd@%d --> %d\n",
+				count, offset, status);
+		return (status < 0) ? -EIO : status;
+	}
+
+	/*
+	 * When we have a better choice than SMBus calls, use a combined
+	 * I2C message. Write address; then read up to io_limit data bytes.
+	 * Note that read page rollover helps us here (unlike writes).
+	 * msgbuf is u8 and will cast to our needs.
+	 */
+	i = 0;
+	if (at24->chip.flags & AT24_FLAG_ADDR16)
+		msgbuf[i++] = offset >> 8;
+	msgbuf[i++] = offset;
+
+	msg[0].addr = client->addr;
+	msg[0].buf = msgbuf;
+	msg[0].len = i;
+
+	msg[1].addr = client->addr;
+	msg[1].flags = I2C_M_RD;
+	msg[1].buf = buf;
+	msg[1].len = count;
+
+	status = i2c_transfer(client->adapter, msg, 2);
+	dev_dbg(&client->dev, "i2c read %zd@%d --> %d\n",
+			count, offset, status);
+
+	if (status == 2)
+		return count;
+	else if (status >= 0)
+		return -EIO;
+	else
+		return status;
+}
+
+static ssize_t at24_bin_read(struct kobject *kobj, struct bin_attribute *attr,
+		char *buf, loff_t off, size_t count)
+{
+	struct at24_data *at24;
+	ssize_t retval = 0;
+
+	at24 = dev_get_drvdata(container_of(kobj, struct device, kobj));
+
+	if (unlikely(!count))
+		return count;
+
+	/*
+	 * Read data from chip, protecting against concurrent updates
+	 * from this host, but not from other I2C masters.
+	 */
+	mutex_lock(&at24->lock);
+
+	while (count) {
+		ssize_t	status;
+
+		status = at24_eeprom_read(at24, buf, off, count);
+		if (status <= 0) {
+			if (retval == 0)
+				retval = status;
+			break;
+		}
+		buf += status;
+		off += status;
+		count -= status;
+		retval += status;
+	}
+
+	mutex_unlock(&at24->lock);
+
+	return retval;
+}
+
+
+/*
+ * REVISIT: export at24_bin{read,write}() to let other kernel code use
+ * eeprom data. For example, it might hold a board's Ethernet address, or
+ * board-specific calibration data generated on the manufacturing floor.
+ */
+
+
+/*
+ * Note that if the hardware write-protect pin is pulled high, the whole
+ * chip is normally write protected. But there are plenty of product
+ * variants here, including OTP fuses and partial chip protect.
+ *
+ * We only use page mode writes; the alternative is sloooow. This routine
+ * writes at most one page.
+ */
+static ssize_t at24_eeprom_write(struct at24_data *at24, char *buf,
+		unsigned offset, size_t count)
+{
+	struct i2c_client *client;
+	struct i2c_msg msg;
+	ssize_t status;
+	unsigned long timeout, write_time;
+	unsigned next_page;
+
+	/* Get corresponding I2C address and adjust offset */
+	client = at24_translate_offset(at24, &offset);
+
+	/* write_max is at most a page */
+	if (count > at24->write_max)
+		count = at24->write_max;
+
+	/* Never roll over backwards, to the start of this page */
+	next_page = roundup(offset + 1, at24->chip.page_size);
+	if (offset + count > next_page)
+		count = next_page - offset;
+
+	/* If we'll use I2C calls for I/O, set up the message */
+	if (!at24->use_smbus) {
+		int i = 0;
+
+		msg.addr = client->addr;
+		msg.flags = 0;
+
+		/* msg.buf is u8 and casts will mask the values */
+		msg.buf = at24->writebuf;
+		if (at24->chip.flags & AT24_FLAG_ADDR16)
+			msg.buf[i++] = offset >> 8;
+
+		msg.buf[i++] = offset;
+		memcpy(&msg.buf[i], buf, count);
+		msg.len = i + count;
+	}
+
+	/*
+	 * Writes fail if the previous one didn't complete yet. We may
+	 * loop a few times until this one succeeds, waiting at least
+	 * long enough for one entire page write to work.
+	 */
+	timeout = jiffies + msecs_to_jiffies(write_timeout);
+	do {
+		write_time = jiffies;
+		if (at24->use_smbus) {
+			status = i2c_smbus_write_i2c_block_data(client,
+					offset, count, buf);
+			if (status == 0)
+				status = count;
+		} else {
+			status = i2c_transfer(client->adapter, &msg, 1);
+			if (status == 1)
+				status = count;
+		}
+		dev_dbg(&client->dev, "write %zd@%d --> %zd (%ld)\n",
+				count, offset, status, jiffies);
+
+		if (status == count)
+			return count;
+
+		/* REVISIT: at HZ=100, this is sloooow */
+		msleep(1);
+	} while (time_before(write_time, timeout));
+
+	return -ETIMEDOUT;
+}
+
+static ssize_t at24_bin_write(struct kobject *kobj, struct bin_attribute *attr,
+		char *buf, loff_t off, size_t count)
+{
+	struct at24_data *at24;
+	ssize_t retval = 0;
+
+	at24 = dev_get_drvdata(container_of(kobj, struct device, kobj));
+
+	if (unlikely(!count))
+		return count;
+
+	/*
+	 * Write data to chip, protecting against concurrent updates
+	 * from this host, but not from other I2C masters.
+	 */
+	mutex_lock(&at24->lock);
+
+	while (count) {
+		ssize_t	status;
+
+		status = at24_eeprom_write(at24, buf, off, count);
+		if (status <= 0) {
+			if (retval == 0)
+				retval = status;
+			break;
+		}
+		buf += status;
+		off += status;
+		count -= status;
+		retval += status;
+	}
+
+	mutex_unlock(&at24->lock);
+
+	return retval;
+}
+
+/*-------------------------------------------------------------------------*/
+
+static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
+{
+	struct at24_platform_data chip;
+	bool writable;
+	bool use_smbus = false;
+	struct at24_data *at24;
+	int err;
+	unsigned i, num_addresses;
+	kernel_ulong_t magic;
+
+	if (client->dev.platform_data) {
+		chip = *(struct at24_platform_data *)client->dev.platform_data;
+	} else {
+		if (!id->driver_data) {
+			err = -ENODEV;
+			goto err_out;
+		}
+		magic = id->driver_data;
+		chip.byte_len = BIT(magic & AT24_BITMASK(AT24_SIZE_BYTELEN));
+		magic >>= AT24_SIZE_BYTELEN;
+		chip.flags = magic & AT24_BITMASK(AT24_SIZE_FLAGS);
+		/*
+		 * This is slow, but we can't know all eeproms, so we better
+		 * play safe. Specifying custom eeprom-types via platform_data
+		 * is recommended anyhow.
+		 */
+		chip.page_size = 1;
+	}
+
+	if (!is_power_of_2(chip.byte_len))
+		dev_warn(&client->dev,
+			"byte_len looks suspicious (no power of 2)!\n");
+	if (!is_power_of_2(chip.page_size))
+		dev_warn(&client->dev,
+			"page_size looks suspicious (no power of 2)!\n");
+
+	/* Use I2C operations unless we're stuck with SMBus extensions. */
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
+		if (chip.flags & AT24_FLAG_ADDR16) {
+			err = -EPFNOSUPPORT;
+			goto err_out;
+		}
+		if (!i2c_check_functionality(client->adapter,
+				I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
+			err = -EPFNOSUPPORT;
+			goto err_out;
+		}
+		use_smbus = true;
+	}
+
+	if (chip.flags & AT24_FLAG_TAKE8ADDR)
+		num_addresses = 8;
+	else
+		num_addresses =	DIV_ROUND_UP(chip.byte_len,
+			(chip.flags & AT24_FLAG_ADDR16) ? 65536 : 256);
+
+	at24 = kzalloc(sizeof(struct at24_data) +
+		num_addresses * sizeof(struct i2c_client *), GFP_KERNEL);
+	if (!at24) {
+		err = -ENOMEM;
+		goto err_out;
+	}
+
+	mutex_init(&at24->lock);
+	at24->use_smbus = use_smbus;
+	at24->chip = chip;
+	at24->num_addresses = num_addresses;
+
+	/*
+	 * Export the EEPROM bytes through sysfs, since that's convenient.
+	 * By default, only root should see the data (maybe passwords etc)
+	 */
+	at24->bin.attr.name = "eeprom";
+	at24->bin.attr.mode = chip.flags & AT24_FLAG_IRUGO ? S_IRUGO : S_IRUSR;
+	at24->bin.attr.owner = THIS_MODULE;
+	at24->bin.read = at24_bin_read;
+	at24->bin.size = chip.byte_len;
+
+	writable = !(chip.flags & AT24_FLAG_READONLY);
+	if (writable) {
+		if (!use_smbus || i2c_check_functionality(client->adapter,
+				I2C_FUNC_SMBUS_WRITE_I2C_BLOCK)) {
+
+			unsigned write_max = chip.page_size;
+
+			at24->bin.write = at24_bin_write;
+			at24->bin.attr.mode |= S_IWUSR;
+
+			if (write_max > io_limit)
+				write_max = io_limit;
+			if (use_smbus && write_max > I2C_SMBUS_BLOCK_MAX)
+				write_max = I2C_SMBUS_BLOCK_MAX;
+			at24->write_max = write_max;
+
+			/* buffer (data + address at the beginning) */
+			at24->writebuf = kmalloc(write_max + 2, GFP_KERNEL);
+			if (!at24->writebuf) {
+				err = -ENOMEM;
+				goto err_struct;
+			}
+		} else {
+			dev_warn(&client->dev,
+				"cannot write due to controller restrictions.");
+		}
+	}
+
+	at24->client[0] = client;
+
+	/* use dummy devices for multiple-address chips */
+	for (i = 1; i < num_addresses; i++) {
+		at24->client[i] = i2c_new_dummy(client->adapter,
+					client->addr + i);
+		if (!at24->client[i]) {
+			dev_err(&client->dev, "address 0x%02x unavailable\n",
+					client->addr + i);
+			err = -EADDRINUSE;
+			goto err_clients;
+		}
+	}
+
+	err = sysfs_create_bin_file(&client->dev.kobj, &at24->bin);
+	if (err)
+		goto err_clients;
+
+	i2c_set_clientdata(client, at24);
+
+	dev_info(&client->dev, "%Zd byte %s EEPROM %s\n",
+		at24->bin.size, client->name,
+		writable ? "(writable)" : "(read-only)");
+	dev_dbg(&client->dev,
+		"page_size %d, num_addresses %d, write_max %d%s\n",
+		chip.page_size, num_addresses,
+		at24->write_max,
+		use_smbus ? ", use_smbus" : "");
+
+	return 0;
+
+err_clients:
+	for (i = 1; i < num_addresses; i++)
+		if (at24->client[i])
+			i2c_unregister_device(at24->client[i]);
+
+	kfree(at24->writebuf);
+err_struct:
+	kfree(at24);
+err_out:
+	dev_dbg(&client->dev, "probe error %d\n", err);
+	return err;
+}
+
+static int __devexit at24_remove(struct i2c_client *client)
+{
+	struct at24_data *at24;
+	int i;
+
+	at24 = i2c_get_clientdata(client);
+	sysfs_remove_bin_file(&client->dev.kobj, &at24->bin);
+
+	for (i = 1; i < at24->num_addresses; i++)
+		i2c_unregister_device(at24->client[i]);
+
+	kfree(at24->writebuf);
+	kfree(at24);
+	i2c_set_clientdata(client, NULL);
+	return 0;
+}
+
+/*-------------------------------------------------------------------------*/
+
+static struct i2c_driver at24_driver = {
+	.driver = {
+		.name = "at24",
+		.owner = THIS_MODULE,
+	},
+	.probe = at24_probe,
+	.remove = __devexit_p(at24_remove),
+	.id_table = at24_ids,
+};
+
+static int __init at24_init(void)
+{
+	io_limit = rounddown_pow_of_two(io_limit);
+	return i2c_add_driver(&at24_driver);
+}
+module_init(at24_init);
+
+static void __exit at24_exit(void)
+{
+	i2c_del_driver(&at24_driver);
+}
+module_exit(at24_exit);
+
+MODULE_DESCRIPTION("Driver for most I2C EEPROMs");
+MODULE_AUTHOR("David Brownell and Wolfram Sang");
+MODULE_LICENSE("GPL");

include/linux/i2c/at24.h

@@ -0,0 +1,28 @@
+#ifndef _LINUX_AT24_H
+#define _LINUX_AT24_H
+
+#include <linux/types.h>
+
+/*
+ * As seen through Linux I2C, differences between the most common types of I2C
+ * memory include:
+ * - How much memory is available (usually specified in bit)?
+ * - What write page size does it support?
+ * - Special flags (16 bit addresses, read_only, world readable...)?
+ *
+ * If you set up a custom eeprom type, please double-check the parameters.
+ * Especially page_size needs extra care, as you risk data loss if your value
+ * is bigger than what the chip actually supports!
+ */
+
+struct at24_platform_data {
+	u32		byte_len;		/* size (sum of all addr) */
+	u16		page_size;		/* for writes */
+	u8		flags;
+#define AT24_FLAG_ADDR16	0x80	/* address pointer is 16 bit */
+#define AT24_FLAG_READONLY	0x40	/* sysfs-entry will be read-only */
+#define AT24_FLAG_IRUGO		0x20	/* sysfs-entry will be world-readable */
+#define AT24_FLAG_TAKE8ADDR	0x10	/* take always 8 addresses (24c00) */
+};
+
+#endif /* _LINUX_AT24_H */