[PATCH 2/3] i2c: stm32f7: flush TX FIFO upon transfer errors

[Alain Volmat <alain.volmat@foss.st.com>]

While handling an error during transfer (ex: NACK), it could
happen that the driver has already written data into the TX Fifo
before the transfer get stopped.
This commit add FIFO Flush after end of transfer in case of error to
avoid sending a wrong data on any other slave upon next transfer.

Fixes: aeb068c57214 ("i2c: i2c-stm32f7: add driver")

Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
---
 drivers/i2c/busses/i2c-stm32f7.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-stm32f7.c b/drivers/i2c/busses/i2c-stm32f7.c
index d596733136c3..0d99c075deb2 100644
--- a/drivers/i2c/busses/i2c-stm32f7.c
+++ b/drivers/i2c/busses/i2c-stm32f7.c
@@ -1696,6 +1696,15 @@ static int stm32f7_i2c_xfer(struct i2c_adapter *i2c_adap,
 	time_left = wait_for_completion_timeout(&i2c_dev->complete,
 						i2c_dev->adap.timeout);
 	ret = f7_msg->result;
+	if (ret) {
+		/*
+		 * It is possible that some unsent data have already been
+		 * written in the TX Fifo. To avoid sending old data in a
+		 * further transfer, flush FIFO in case of any error
+		 */
+		writel_relaxed(STM32F7_I2C_ISR_TXE,
+			       i2c_dev->base + STM32F7_I2C_ISR);
+	}
 
 	if (!time_left) {
 		dev_dbg(i2c_dev->dev, "Access to slave 0x%x timed out\n",
@@ -1745,8 +1754,16 @@ static int stm32f7_i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr,
 	timeout = wait_for_completion_timeout(&i2c_dev->complete,
 					      i2c_dev->adap.timeout);
 	ret = f7_msg->result;
-	if (ret)
+	if (ret) {
+		/*
+		 * It is possible that some unsent data have already been
+		 * written in the TX Fifo. To avoid sending old data in a
+		 * further transfer, flush FIFO in case of any error
+		 */
+		writel_relaxed(STM32F7_I2C_ISR_TXE,
+			       i2c_dev->base + STM32F7_I2C_ISR);
 		goto pm_free;
+	}
 
 	if (!timeout) {
 		dev_dbg(dev, "Access to slave 0x%x timed out\n", f7_msg->addr);
-- 
2.25.1


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