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spi: a3700: Clear DATA_OUT when performing a read 

[ Upstream commit 44a5f423e7 ]

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>
pull/10/head
Maxime Chevallier 2018-01-17 17:15:25 +01:00 committed by Greg Kroah-Hartman
parent 5bb5b9c681
commit 58bc0fd843
1 changed files with 5 additions and 0 deletions
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5
drivers/spi/spi-armada-3700.c
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@ -624,6 +624,11 @@ 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);