4.14-stable review patch. If anyone has any objections, please let me know.
------------------
From: Maxime Chevallier <maxime.chevallier@xxxxxxxx>
[ 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 <maxime.chevallier@xxxxxxxx>
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/spi/spi-armada-3700.c | 5 +++++
1 file changed, 5 insertions(+)
--- a/drivers/spi/spi-armada-3700.c
+++ b/drivers/spi/spi-armada-3700.c
@@ -624,6 +624,11 @@ static int a3700_spi_transfer_one(struct
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);