4.14-stable review patch. If anyone has any objections, please let me know.
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From: Maxime Chevallier maxime.chevallier@smile.fr
[ 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@smile.fr Signed-off-by: Mark Brown broonie@kernel.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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);