Commit e32213fb authored by Sven Van Asbroeck's avatar Sven Van Asbroeck Committed by Bartosz Golaszewski
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eeprom: at24: support eeproms that do not auto-rollover reads 



Some multi-address eeproms in the at24 family may not automatically
roll-over reads to the next slave address. On those eeproms, reads
that straddle slave boundaries will not work correctly.

Solution:
Mark such eeproms with a flag that prevents reads straddling
slave boundaries. Add the AT24_FLAG_NO_RDROL flag to the eeprom
entry in the device_id table, or add 'no-read-rollover' to the
eeprom devicetree entry.

Note that I have not personally enountered an at24 chip that
does not support read rollovers. They may or may not exist.
However, my hardware requires this functionality because of
a quirk.

Signed-off-by: default avatarSven Van Asbroeck <svendev@arcx.com>
Signed-off-by: default avatarBartosz Golaszewski <brgl@bgdev.pl>
parent 355dd4ca

drivers/misc/eeprom/at24.c

+27 −12
Original line number Diff line number Diff line
@@ -251,15 +251,6 @@ MODULE_DEVICE_TABLE(acpi, at24_acpi_ids); 
 * 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.

 *

 * 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.

 */

static struct at24_client *at24_translate_offset(struct at24_data *at24,

						 unsigned int *offset)
@@ -277,6 +268,30 @@ static struct at24_client *at24_translate_offset(struct at24_data *at24, 
	return &at24->client[i];

}



static size_t at24_adjust_read_count(struct at24_data *at24,

				      unsigned int offset, size_t count)

{

	unsigned int bits;

	size_t remainder;



	/*

	 * In case of multi-address chips that don't rollover reads to

	 * the next slave address: truncate the count to the slave boundary,

	 * so that the read never straddles slaves.

	 */

	if (at24->chip.flags & AT24_FLAG_NO_RDROL) {

		bits = (at24->chip.flags & AT24_FLAG_ADDR16) ? 16 : 8;

		remainder = BIT(bits) - offset;

		if (count > remainder)

			count = remainder;

	}



	if (count > io_limit)

		count = io_limit;



	return count;

}



static ssize_t at24_regmap_read(struct at24_data *at24, char *buf,

				unsigned int offset, size_t count)

{
@@ -289,9 +304,7 @@ static ssize_t at24_regmap_read(struct at24_data *at24, char *buf, 
	at24_client = at24_translate_offset(at24, &offset);

	regmap = at24_client->regmap;

	client = at24_client->client;



	if (count > io_limit)

		count = io_limit;

	count = at24_adjust_read_count(at24, offset, count);



	/* adjust offset for mac and serial read ops */

	offset += at24->offset_adj;
@@ -457,6 +470,8 @@ static void at24_get_pdata(struct device *dev, struct at24_platform_data *chip) 


	if (device_property_present(dev, "read-only"))

		chip->flags |= AT24_FLAG_READONLY;

	if (device_property_present(dev, "no-read-rollover"))

		chip->flags |= AT24_FLAG_NO_RDROL;



	err = device_property_read_u32(dev, "size", &val);

	if (!err)

include/linux/platform_data/at24.h

+2 −0
Original line number Diff line number Diff line
@@ -50,6 +50,8 @@ struct at24_platform_data { 
#define AT24_FLAG_TAKE8ADDR	BIT(4)	/* take always 8 addresses (24c00) */

#define AT24_FLAG_SERIAL	BIT(3)	/* factory-programmed serial number */

#define AT24_FLAG_MAC		BIT(2)	/* factory-programmed mac address */

#define AT24_FLAG_NO_RDROL  BIT(1)	/* does not auto-rollover reads to */

					/* the next slave address */



	void		(*setup)(struct nvmem_device *nvmem, void *context);

	void		*context;

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