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>
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@ -251,15 +251,6 @@ MODULE_DEVICE_TABLE(acpi, at24_acpi_ids);
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* Slave address and byte offset derive from the offset. Always
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* set the byte address; on a multi-master board, another master
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* may have changed the chip's "current" address pointer.
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*
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* REVISIT some multi-address chips don't rollover page reads to
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* the next slave address, so we may need to truncate the count.
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* Those chips might need another quirk flag.
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*
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* If the real hardware used four adjacent 24c02 chips and that
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* were misconfigured as one 24c08, that would be a similar effect:
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* one "eeprom" file not four, but larger reads would fail when
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* they crossed certain pages.
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*/
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static struct at24_client *at24_translate_offset(struct at24_data *at24,
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unsigned int *offset)
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@ -277,6 +268,30 @@ static struct at24_client *at24_translate_offset(struct at24_data *at24,
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return &at24->client[i];
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}
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static size_t at24_adjust_read_count(struct at24_data *at24,
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unsigned int offset, size_t count)
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{
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unsigned int bits;
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size_t remainder;
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/*
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* In case of multi-address chips that don't rollover reads to
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* the next slave address: truncate the count to the slave boundary,
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* so that the read never straddles slaves.
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*/
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if (at24->chip.flags & AT24_FLAG_NO_RDROL) {
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bits = (at24->chip.flags & AT24_FLAG_ADDR16) ? 16 : 8;
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remainder = BIT(bits) - offset;
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if (count > remainder)
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count = remainder;
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}
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if (count > io_limit)
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count = io_limit;
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return count;
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}
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static ssize_t at24_regmap_read(struct at24_data *at24, char *buf,
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unsigned int offset, size_t count)
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{
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@ -289,9 +304,7 @@ static ssize_t at24_regmap_read(struct at24_data *at24, char *buf,
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at24_client = at24_translate_offset(at24, &offset);
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regmap = at24_client->regmap;
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client = at24_client->client;
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if (count > io_limit)
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count = io_limit;
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count = at24_adjust_read_count(at24, offset, count);
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/* adjust offset for mac and serial read ops */
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offset += at24->offset_adj;
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@ -457,6 +470,8 @@ static void at24_get_pdata(struct device *dev, struct at24_platform_data *chip)
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if (device_property_present(dev, "read-only"))
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chip->flags |= AT24_FLAG_READONLY;
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if (device_property_present(dev, "no-read-rollover"))
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chip->flags |= AT24_FLAG_NO_RDROL;
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err = device_property_read_u32(dev, "size", &val);
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if (!err)
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@ -50,6 +50,8 @@ struct at24_platform_data {
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#define AT24_FLAG_TAKE8ADDR BIT(4) /* take always 8 addresses (24c00) */
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#define AT24_FLAG_SERIAL BIT(3) /* factory-programmed serial number */
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#define AT24_FLAG_MAC BIT(2) /* factory-programmed mac address */
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#define AT24_FLAG_NO_RDROL BIT(1) /* does not auto-rollover reads to */
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/* the next slave address */
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void (*setup)(struct nvmem_device *nvmem, void *context);
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void *context;
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