[PATCH v2 2/4] i2c: imx: Fix race condition in dma read

[Esben Haabendal]

From: Esben Haabendal <e...@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 <e...@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