From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Maxime Chevallier , Mark Brown , Sasha Levin Subject: [PATCH 4.14 052/183] spi: a3700: Clear DATA_OUT when performing a read Date: Wed, 25 Apr 2018 12:34:32 +0200 Message-Id: <20180425103244.645304344@linuxfoundation.org> In-Reply-To: <20180425103242.532713678@linuxfoundation.org> References: <20180425103242.532713678@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ 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 Signed-off-by: Greg Kroah-Hartman --- 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);