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>

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index 3fd26d7cb50e79808282f11ee76e77d9760fd7d3..848fda8be3145af492a8bec79a260c00037719a5 100644 (file)
--- 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)

diff --git a/include/linux/platform_data/at24.h b/include/linux/platform_data/at24.h
index 271a4e25af67d4bdb78781455a4b7a3679010872..841bb2815a4105e8e4e93eadeee126e842088728 100644 (file)
--- a/include/linux/platform_data/at24.h
+++ b/include/linux/platform_data/at24.h
@@ -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;