[PATCH 1/2] i2c: imx: do not carry the interrupt status over to the next transfer

[Mehmet Fide <mehmet.fide@gmail.com>]

From: Mehmet Fide <mehmet.fide@screeningeagle.com>

In DMA mode the interrupt handler stores I2SR in i2c_imx->i2csr and only
i2c_imx_trx_complete() clears it. A DMA transfer that fails returns
without doing so, for example a DMA write whose address is not
acknowledged.

The stale status stays until the next DMA read. There
i2c_imx_prepare_read() calls i2c_imx_trx_complete(), which finds IIF set
and returns before the address byte has been sent, so the read returns
0xff for every byte without an error:

  i2ctransfer -a -y 0 w20@0x03 0x00-     # unused address, -ETIMEDOUT
  i2ctransfer -y 0 w1@0x54 0x00 r32      # 32 times 0xff
  i2ctransfer -y 0 w1@0x54 0x00 r32      # correct data

Clear the status when a transfer starts.

Fixes: ce1a78840ff7 ("i2c: imx: add DMA support for freescale i2c driver")
Cc: stable@vger.kernel.org
Signed-off-by: Mehmet Fide <mehmet.fide@screeningeagle.com>
---
 drivers/i2c/busses/i2c-imx.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index ccf08cd63151..1987a0fd8132 100644
--- a/drivers/i2c/busses/i2c-imx.c
+++ b/drivers/i2c/busses/i2c-imx.c
@@ -1657,6 +1657,8 @@ static int i2c_imx_xfer_common(struct i2c_adapter *adapter,
 	if (result)
 		return result;
 
+	i2c_imx->i2csr = 0;
+
 	/* Start I2C transfer */
 	result = i2c_imx_start(i2c_imx, atomic);
 	if (result) {
-- 
2.56.0