[PATCH AUTOSEL for 4.15 043/189] spi: a3700: Clear DATA_OUT when performing a read

[Sasha Levin]

From: Maxime Chevallier 

[ Upstream commit 44a5f423e70374e5b42cecd85e78f2d79334e0f2 ]

When performing a read using FIFO mode, the spi controller shifts out
the last 2 bytes that were written in a previous transfer on MOSI.

This undocumented behaviour can cause devices to misinterpret the
transfer, so we explicitly clear the WFIFO before each read.

This behaviour was noticed on EspressoBin.

Signed-off-by: Maxime Chevallier 
Signed-off-by: Mark Brown 
Signed-off-by: Sasha Levin 
---
 drivers/spi/spi-armada-3700.c | 5 +
 1 file changed, 5 insertions(+)

diff --git a/drivers/spi/spi-armada-3700.c b/drivers/spi/spi-armada-3700.c
index d65345312527..c11ea6c169a4 100644
--- a/drivers/spi/spi-armada-3700.c
+++ b/drivers/spi/spi-armada-3700.c
@@ -615,6 +615,11 @@ static int a3700_spi_transfer_one(struct spi_master 
*master,
a3700_spi_header_set(a3700_spi);
 
if (xfer->rx_buf) {
+   /* Clear WFIFO, since it's last 2 bytes are shifted out during
+* a read operation
+*/
+   spireg_write(a3700_spi, A3700_SPI_DATA_OUT_REG, 0);
+
/* Set read data length */
spireg_write(a3700_spi, A3700_SPI_IF_DIN_CNT_REG,
 a3700_spi->buf_len);
-- 
2.15.1

[PATCH AUTOSEL for 4.15 043/189] spi: a3700: Clear DATA_OUT when performing a read

[Sasha Levin]

From: Maxime Chevallier 

[ Upstream commit 44a5f423e70374e5b42cecd85e78f2d79334e0f2 ]

When performing a read using FIFO mode, the spi controller shifts out
the last 2 bytes that were written in a previous transfer on MOSI.

This undocumented behaviour can cause devices to misinterpret the
transfer, so we explicitly clear the WFIFO before each read.

This behaviour was noticed on EspressoBin.

Signed-off-by: Maxime Chevallier 
Signed-off-by: Mark Brown 
Signed-off-by: Sasha Levin 
---
 drivers/spi/spi-armada-3700.c | 5 +
 1 file changed, 5 insertions(+)

diff --git a/drivers/spi/spi-armada-3700.c b/drivers/spi/spi-armada-3700.c
index d65345312527..c11ea6c169a4 100644
--- a/drivers/spi/spi-armada-3700.c
+++ b/drivers/spi/spi-armada-3700.c
@@ -615,6 +615,11 @@ static int a3700_spi_transfer_one(struct spi_master 
*master,
a3700_spi_header_set(a3700_spi);
 
if (xfer->rx_buf) {
+   /* Clear WFIFO, since it's last 2 bytes are shifted out during
+* a read operation
+*/
+   spireg_write(a3700_spi, A3700_SPI_DATA_OUT_REG, 0);
+
/* Set read data length */
spireg_write(a3700_spi, A3700_SPI_IF_DIN_CNT_REG,
 a3700_spi->buf_len);
-- 
2.15.1