i2c: npcm7xx: Clear LAST bit after a failed transaction.

Due to a HW issue, in some scenarios the LAST bit might remain set.
This will cause an unexpected NACK after reading 16 bytes on the next
read.

Example: if user tries to read from a missing device, get a NACK,
then if the next command is a long read ( > 16 bytes),
the master will stop reading after 16 bytes.
To solve this, if a command fails, check if LAST bit is still
set. If it does, reset the module.

Fixes: 56a1485b102e (i2c: npcm7xx: Add Nuvoton NPCM I2C controller driver)
Signed-off-by: Tali Perry <tali.perry1@gmail.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

diff --git a/drivers/i2c/busses/i2c-npcm7xx.c b/drivers/i2c/busses/i2c-npcm7xx.c
index dfcf04e..2ad1663 100644 (file)
--- a/drivers/i2c/busses/i2c-npcm7xx.c
+++ b/drivers/i2c/busses/i2c-npcm7xx.c
@@ -2163,6 +2163,15 @@ static int npcm_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
        if (bus->cmd_err == -EAGAIN)
                ret = i2c_recover_bus(adap);
 
+       /*
+        * After any type of error, check if LAST bit is still set,
+        * due to a HW issue.
+        * It cannot be cleared without resetting the module.
+        */
+       if (bus->cmd_err &&
+           (NPCM_I2CRXF_CTL_LAST_PEC & ioread8(bus->reg + NPCM_I2CRXF_CTL)))
+               npcm_i2c_reset(bus);
+
 #if IS_ENABLED(CONFIG_I2C_SLAVE)
        /* reenable slave if it was enabled */
        if (bus->slave)