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From: Esben Haabendal <esben.haabendal@gmail.com>
To: linux-i2c@vger.kernel.org
Cc: "Wolfram Sang" <wsa+renesas@sang-engineering.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Yuan Yao" <yao.yuan@freescale.com>,
	"Esben Haabendal" <eha@deif.com>,
	"Fabio Estevam" <fabio.estevam@nxp.com>,
	"Lucas Stach" <l.stach@pengutronix.de>,
	"Phil Reid" <preid@electromag.com.au>,
	"Clemens Gruber" <clemens.gruber@pqgruber.com>,
	"Peter Rosin" <peda@axentia.se>,
	linux-kernel@vger.kernel.org
Subject: [PATCH v2 2/4] i2c: imx: Fix race condition in dma read
Date: Mon,  9 Jul 2018 11:43:02 +0200
Message-ID: <20180709094304.8814-3-esben.haabendal@gmail.com> (raw)
In-Reply-To: <20180709094304.8814-1-esben.haabendal@gmail.com>

From: Esben Haabendal <eha@deif.com>

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 <eha@deif.com>
---
 drivers/i2c/busses/i2c-imx.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index 39cfd98c7b23..d86f152176a4 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;
@@ -810,6 +807,11 @@ 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;
 	imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
+	if (i2c_imx->dma && msgs->len >= DMA_THRESHOLD && !block_data) {
+		temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
+		temp |= I2CR_DMAEN;
+		imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
+	}
 	imx_i2c_read_reg(i2c_imx, IMX_I2C_I2DR); /* dummy read */
 
 	dev_dbg(&i2c_imx->adapter.dev, "<%s> read data\n", __func__);
-- 
2.18.0


  parent reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20180709094304.8814-1-esben.haabendal@gmail.com>
2018-07-09  9:43 ` [PATCH v2 1/4] i2c: imx: Fix reinit_completion() use Esben Haabendal
2018-07-23 18:08   ` Wolfram Sang
2018-07-09  9:43 ` Esben Haabendal [this message]
2018-07-24  7:57   ` [PATCH v2 2/4] i2c: imx: Fix race condition in dma read Uwe Kleine-König
2018-08-09 11:57     ` Esben Haabendal
2018-07-09  9:43 ` [PATCH v2 3/4] i2c: imx: Simplify stopped state tracking Esben Haabendal
2018-07-24  7:59   ` Uwe Kleine-König
2018-08-09 12:06     ` Esben Haabendal
2018-08-09 16:26       ` Uwe Kleine-König
2018-08-10  9:25         ` Esben Haabendal
2018-08-10 12:25           ` Uwe Kleine-König
2018-07-09  9:43 ` [PATCH v2 4/4] arm: dts: ls1021a: Enable I2C DMA support Esben Haabendal
2018-07-24  8:02   ` Uwe Kleine-König

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