Messages in this thread Patch in this message | | | From | Maxime Chevallier <> | Subject | [PATCH 1/4] spi: a3700: Clear DATA_OUT when performing a read | Date | Wed, 17 Jan 2018 17:15:25 +0100 |
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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> --- 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 d653453..c11ea6c 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); -- 2.1.4
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