From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-sn1nam01on0134.outbound.protection.outlook.com ([104.47.32.134]:37792 "EHLO NAM01-SN1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754735AbeDIAWv (ORCPT ); Sun, 8 Apr 2018 20:22:51 -0400 From: Sasha Levin To: "stable@vger.kernel.org" , "linux-kernel@vger.kernel.org" CC: Maxime Chevallier , Mark Brown , Sasha Levin Subject: [PATCH AUTOSEL for 4.14 038/161] spi: a3700: Clear DATA_OUT when performing a read Date: Mon, 9 Apr 2018 00:20:14 +0000 Message-ID: <20180409001936.162706-38-alexander.levin@microsoft.com> References: <20180409001936.162706-1-alexander.levin@microsoft.com> In-Reply-To: <20180409001936.162706-1-alexander.levin@microsoft.com> Content-Language: en-US Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org List-ID: 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 --- 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 fe3fa1e8517a..4903f15177cf 100644 --- 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 spi_master *m= aster, a3700_spi_header_set(a3700_spi); =20 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); --=20 2.15.1