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authorSven Van Asbroeck <svendev@arcx.com>2017-12-08 11:28:30 -0500
committerBartosz Golaszewski <brgl@bgdev.pl>2018-01-01 19:40:48 +0100
commite32213fbc5432c28268dced0dc8735dcf8532d36 (patch)
treea5b25dc3be738432c982d5013f7335c533e7ab6f /drivers/misc
parent355dd4ca10b49183272ec54ed9853bb4b95d2391 (diff)
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/misc')
-rw-r--r--drivers/misc/eeprom/at24.c39
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)

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