i2c: imx: Fix race condition in dma read

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>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: stable@kernel.org

diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index 0207e194f84bb4e667d4ebec548987f40caffdd1..eb11ac3d6aba5c66fb243ec96ecf2f7e1a2237fa 100644 (file)
--- 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;
@@ -784,6 +781,7 @@ static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs, bo
        int i, result;
        unsigned int temp;
        int block_data = msgs->flags & I2C_M_RECV_LEN;
+       int use_dma = i2c_imx->dma && msgs->len >= DMA_THRESHOLD && !block_data;
 
        dev_dbg(&i2c_imx->adapter.dev,
                "<%s> write slave address: addr=0x%x\n",
@@ -810,12 +808,14 @@ 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 (use_dma)
+               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__);
 
-       if (i2c_imx->dma && msgs->len >= DMA_THRESHOLD && !block_data)
+       if (use_dma)
                return i2c_imx_dma_read(i2c_imx, msgs, is_lastmsg);
 
        /* read data */