i2c: rcar: document HW incapabilities

Add recent findings (IGNORE_NAK) and document in a bit more detail why
the feature is not possible.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

diff --git a/drivers/i2c/busses/i2c-rcar.c b/drivers/i2c/busses/i2c-rcar.c
index 214a71c..030952e 100644 (file)
--- a/drivers/i2c/busses/i2c-rcar.c
+++ b/drivers/i2c/busses/i2c-rcar.c
@@ -783,7 +783,12 @@ static int rcar_unreg_slave(struct i2c_client *slave)
 
 static u32 rcar_i2c_func(struct i2c_adapter *adap)
 {
-       /* This HW can't do SMBUS_QUICK and NOSTART */
+       /*
+        * This HW can't do:
+        * I2C_SMBUS_QUICK (setting FSB during START didn't work)
+        * I2C_M_NOSTART (automatically sends address after START)
+        * I2C_M_IGNORE_NAK (automatically sends STOP after NAK)
+        */
        return I2C_FUNC_I2C | I2C_FUNC_SLAVE |
                (I2C_FUNC_SMBUS_EMUL & ~I2C_FUNC_SMBUS_QUICK);
 }