i2c: slave-eeprom: add more info when to increase the pointer

It is a bit subtle when to correctly increase the buffer index when
reading. Make this clearer by adding some more comments and pointers to
the docs.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/i2c/i2c-slave-eeprom.c b/drivers/i2c/i2c-slave-eeprom.c
index 3fb45d894d80..822374654609 100644
--- a/drivers/i2c/i2c-slave-eeprom.c
+++ b/drivers/i2c/i2c-slave-eeprom.c
@@ -48,12 +48,18 @@ static int i2c_slave_eeprom_slave_cb(struct i2c_client *client,
                 break;
 
         case I2C_SLAVE_READ_PROCESSED:
+                /* The previous byte made it to the bus, get next one */
                 eeprom->buffer_idx++;
                 /* fallthrough */
         case I2C_SLAVE_READ_REQUESTED:
                 spin_lock(&eeprom->buffer_lock);
                 *val = eeprom->buffer[eeprom->buffer_idx];
                 spin_unlock(&eeprom->buffer_lock);
+                /*
+                 * Do not increment buffer_idx here, because we don't know if
+                 * this byte will be actually used. Read Linux I2C slave docs
+                 * for details.
+                 */
                 break;
 
         case I2C_SLAVE_STOP: