2018-08-09 12:33:27

by Esben Haabendal

Subject: [PATCH v3 1/3] i2c: imx: Fix race condition in dma read

From: Esben Haabendal <[email protected]>

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 <[email protected]>
---
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

2018-08-16 15:58:44

by Uwe Kleine-König

Subject: Re: [PATCH v3 1/3] i2c: imx: Fix race condition in dma read

On Thu, Aug 09, 2018 at 02:32:05PM +0200, Esben Haabendal wrote:
> From: Esben Haabendal <[email protected]>
>
> 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 <[email protected]>
> ---
> 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;

Instead of duplicating the if condition I'd do:

int use_dma = i2c_imx->dma && msgs->len >= DMA_THRESHOLD && !block_data;

and then simplify the two conditions to just "use_dma".

With this changed you can add my Ack.

Best regards
Uwe

--
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Industrial Linux Solutions | http://www.pengutronix.de/ |