Re: [PATCH v4] New-style EEPROM driver using device_ids (superseding the old eeprom driver)

[Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>]

Hi Wolfram,

On Tue, 01 Jul 2008 19:22:09 +0200, Wolfram Sang wrote:
> 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-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
> ---
> 
> Updates since last version:
> 
>  - fixed everything Jean mentioned in the last review
>  - now platform_data has higher priority than device_ids
>  - page_sizes for default values are always 1
>  - change code for calculating num_addresses
>  - cleaning up comments

Great. The code looks very nice now, I think it's ready for merge.
There are a few comments below, but I'll update the code myself, no
need to resend. Any further change to this driver should be submitted
as an incremental patch. Thanks!

> 
> Updates since last version:
> 
>  - added device_ids for common eeprom types (parameters encoded in
>    a 'magic' driver_data value)
>  - removed platform_data entry 'i2c_addr_mask' and calculated
>    its value from other parameters
>  - added 24c00-quirk flag (it covers 8 addresses)
>  - added a flag to make eeproms world-readable (used for spd)
>  - rewrote code that adds an i2c-address to an i2c-message
>  - rewrote code which truncates to page_size
>  - removed 'addr'-variable from eeprom-functions; i2c-address is
>    now taken from the corresponding client-structure
>  - write buffer now allocated once in probe
>  - removed some sanity checks for file offsets as they are handled at
>    the sysfs-layer already.
>  - fixed typos and corrected spellings in comments and Kconfig
>  - renamed some functions to be more self-explanatory
>  - added includes
>  - further cleanups and simplifications
>  - added myself as another author
> 
> Updates since last version:
> 
>  - revisited includes
>  - made write-timeout a module parameter
>  - array of clients is allocated dynamically
>  - removed unnecessary indentation within code
>  - formatted comments
>  - replaced at24_ee_address with a simpler function
>  - at24_ee_write now really waits till timeout
>  - added simple checks of provided eeprom chip data in at24_probe
>  - added comment in at24.h about double-checking custom data
>  - minor fixes
> 
> Updates in this version:
> 
>  - move chip data out of the driver into a seperate .h-file
>  - prefix defined constants with AT24_
>  - make bin file readonly if requested by flags
>  - introduce AT24_MAX_CLIENTS
>  - bugfix: check correct retval in at24_ee_write
> 
> 
> 
>  drivers/i2c/chips/Kconfig  |   26 ++
>  drivers/i2c/chips/Makefile |    1 
>  drivers/i2c/chips/at24.c   |  585 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/i2c/at24.h   |   28 ++
>  4 files changed, 640 insertions(+), 0 deletions(-)
>  create mode 100644 drivers/i2c/chips/at24.c
>  create mode 100644 include/linux/i2c/at24.h
> 
> diff --git a/drivers/i2c/chips/Kconfig b/drivers/i2c/chips/Kconfig
> index 2da2edf..cb01638 100644
> --- a/drivers/i2c/chips/Kconfig
> +++ b/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
> diff --git a/drivers/i2c/chips/Makefile b/drivers/i2c/chips/Makefile
> index e47aca0..39e3e69 100644
> --- a/drivers/i2c/chips/Makefile
> +++ b/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
> diff --git a/drivers/i2c/chips/at24.c b/drivers/i2c/chips/at24.c
> new file mode 100644
> index 0000000..f346b9e
> --- /dev/null
> +++ b/drivers/i2c/chips/at24.c
> @@ -0,0 +1,585 @@
> +/*
> + * 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);

No longer changeable at run-time? I don't mind, but I'm curious why you
changed it.

> +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) },
> +	/* pcf8570 has SRAM only, write it all */
> +	{ "pcf8570", AT24_DEVICE_MAGIC(2048 / 8, 0) },

Now that you use page-size of 1 in all cases, this comment is a bit
confusing. And I am curious if anyone will use this entry, given that
its the same as "24c02", and anyone who is certain to have a PCF8570
would provide platform data to take benefit of the lack of pages of
this chip.

I would at least remove the second part of the comment, and maybe even
the entry, unless you add a new flag AT2C_FLAG_SRAM which automatically
sets a large page size (if that makes sense) or restore the possibility
to set the page size, just for this entry.

> +	{ "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);

Extra parentheses wouldn't hurt... I wouldn't know off the top of my
head, which of & and ?: has greater precedence.

> +
> +	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");
> diff --git a/include/linux/i2c/at24.h b/include/linux/i2c/at24.h
> new file mode 100644
> index 0000000..f6edd52
> --- /dev/null
> +++ b/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 */

-- 
Jean Delvare

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