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author | Sven Van Asbroeck <svendev@arcx.com> | 2017-12-08 11:28:30 -0500 |
---|---|---|
committer | Bartosz Golaszewski <brgl@bgdev.pl> | 2018-01-01 19:40:48 +0100 |
commit | e32213fbc5432c28268dced0dc8735dcf8532d36 (patch) | |
tree | a5b25dc3be738432c982d5013f7335c533e7ab6f /drivers | |
parent | 355dd4ca10b49183272ec54ed9853bb4b95d2391 (diff) | |
download | linux-e32213fbc5432c28268dced0dc8735dcf8532d36.tar.bz2 |
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: Sven Van Asbroeck <svendev@arcx.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Diffstat (limited to 'drivers')
-rw-r--r-- | drivers/misc/eeprom/at24.c | 39 |
1 files changed, 27 insertions, 12 deletions
diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c index 3fd26d7cb50e..848fda8be314 100644 --- a/drivers/misc/eeprom/at24.c +++ b/drivers/misc/eeprom/at24.c @@ -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) |