From mboxrd@z Thu Jan 1 00:00:00 1970 From: Esben Haabendal Subject: [PATCH v3 1/3] i2c: imx: Fix race condition in dma read Date: Thu, 9 Aug 2018 14:32:05 +0200 Message-ID: <20180809123207.9732-2-esben.haabendal@gmail.com> References: <20180809123207.9732-1-esben.haabendal@gmail.com> Return-path: In-Reply-To: <20180809123207.9732-1-esben.haabendal@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: linux-i2c@vger.kernel.org Cc: Esben Haabendal , Wolfram Sang , =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= , Lucas Stach , Linus Walleij , Peter Rosin , Wei Jinhua , Phil Reid , Fabio Estevam , linux-kernel@vger.kernel.org List-Id: linux-i2c@vger.kernel.org From: Esben Haabendal This fixes a race condition, where the DMAEN bit ends up being set after I2C slave has transmitted a byte following the dummy read. When that happens, an interrupt is generated instead, and no DMA request is generated to kickstart the DMA read, and a timeout happens after DMA_TIMEOUT (1 sec). Fixed by setting the DMAEN bit before the dummy read. Signed-off-by: Esben Haabendal --- drivers/i2c/busses/i2c-imx.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c index 498c5e891649..f7bd6c21da27 100644 --- a/drivers/i2c/busses/i2c-imx.c +++ b/drivers/i2c/busses/i2c-imx.c @@ -668,9 +668,6 @@ static int i2c_imx_dma_read(struct imx_i2c_struct *i2c_imx, struct imx_i2c_dma *dma = i2c_imx->dma; struct device *dev = &i2c_imx->adapter.dev; - temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR); - temp |= I2CR_DMAEN; - imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR); dma->chan_using = dma->chan_rx; dma->dma_transfer_dir = DMA_DEV_TO_MEM; @@ -809,6 +806,8 @@ static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs, bo */ if ((msgs->len - 1) || block_data) temp &= ~I2CR_TXAK; + if (i2c_imx->dma && msgs->len >= DMA_THRESHOLD && !block_data) + temp |= I2CR_DMAEN; imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR); imx_i2c_read_reg(i2c_imx, IMX_I2C_I2DR); /* dummy read */ -- 2.18.0