i2c: i2c-bfin-twi: Illegal i2c bus lock upon certain transfer scenarios.

For transfer counts > 255 bytes i2c-bfin-twi sets the data
transfer counter DCNT to 0xFF indicating unlimited transfers.
It then uses a flag iface->manual_stop to manually issue the STOP
condition, once the required amount of bytes are received.

We found that on I2C receive operation issuing the STOP condition
together with a FULL RCV FIFO (2bytes) will cause SDA and SCL be
constantly driven low.

Temporary workaround until further investigation:
Discard the RCV FIFO before issuing the STOP condition.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/i2c/busses/i2c-bfin-twi.c b/drivers/i2c/busses/i2c-bfin-twi.c
index 515822429b19..c2e6b7849e8d 100644
--- a/drivers/i2c/busses/i2c-bfin-twi.c
+++ b/drivers/i2c/busses/i2c-bfin-twi.c
@@ -131,6 +131,10 @@ static void bfin_twi_handle_interrupt(struct bfin_twi_iface *iface,
                         iface->transPtr++;
                         iface->readNum--;
                 } else if (iface->manual_stop) {
+                        /* Temporary workaround to avoid possible bus stall -
+                         * Flush FIFO before issuing the STOP condition
+                         */
+                        read_RCV_DATA16(iface);
                         write_MASTER_CTL(iface,
                                 read_MASTER_CTL(iface) | STOP);
                 } else if (iface->cur_mode == TWI_I2C_MODE_REPEAT &&