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eeprom: at24: support eeproms that do not auto-rollover reads

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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: Sven Van Asbroeck <svendev@arcx.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
This commit is contained in:
Sven Van Asbroeck 2017-12-08 11:28:30 -05:00 committed by Bartosz Golaszewski
parent 355dd4ca10
commit e32213fbc5
2 changed files with 29 additions and 12 deletions
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39
drivers/misc/eeprom/at24.c
View File

@ -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)

2
include/linux/platform_data/at24.h
View File

@ -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;