On Thu, Jun 15, 2017 at 12:30 PM, Wolfram Sang
<wsa+renesas@xxxxxxxxxxxxxxxxxxxx> wrote:
> Handling this is special for this driver. Because the hardware needs to
> initialize the next message in interrupt context, we cannot use the
> i2c_check_msg_for_dma() directly. This helper only works reliably in
> process context. So, we need to check during initial preparation of the
> whole transfer and need to disable DMA completely for the whole transfer
> once a message with a not-DMA-capable buffer is found.
>
> Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Wolfram Sang <wsa@xxxxxxxxxxxxx>
> ---
> drivers/i2c/busses/i2c-rcar.c | 18 +++++++++++++-----
> 1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-rcar.c b/drivers/i2c/busses/i2c-rcar.c
> index 8be3e6cb8fe686..2b679ba4b75066 100644
> --- a/drivers/i2c/busses/i2c-rcar.c
> +++ b/drivers/i2c/busses/i2c-rcar.c
> @@ -111,8 +111,11 @@
> #define ID_ARBLOST (1 << 3)
> #define ID_NACK (1 << 4)
> /* persistent flags */
> +#define ID_P_NODMA (1 << 30)
> #define ID_P_PM_BLOCKED (1 << 31)
> -#define ID_P_MASK ID_P_PM_BLOCKED
> +#define ID_P_MASK (ID_P_PM_BLOCKED | ID_P_NODMA)
> +
> +#define RCAR_DMA_THRESHOLD 8
>
> enum rcar_i2c_type {
> I2C_RCAR_GEN1,
> @@ -358,8 +361,7 @@ static void rcar_i2c_dma(struct rcar_i2c_priv *priv)
> unsigned char *buf;
> int len;
>
> - /* Do not use DMA if it's not available or for messages < 8 bytes */
> - if (IS_ERR(chan) || msg->len < 8)
> + if (IS_ERR(chan) || msg->len < RCAR_DMA_THRESHOLD || priv->flags & ID_P_NODMA)
Might be more efficient to check for ID_P_NODMA first instead of msg->len.
> return;
>
> if (read) {
> @@ -657,11 +659,15 @@ static void rcar_i2c_request_dma(struct rcar_i2c_priv *priv,
> struct i2c_msg *msg)
> {
> struct device *dev = rcar_i2c_priv_to_dev(priv);
> - bool read;
> + bool read = msg->flags & I2C_M_RD;
> struct dma_chan *chan;
> enum dma_transfer_direction dir;
>
> - read = msg->flags & I2C_M_RD;
> + /* we need to check here because we need the 'current' context */
> + if (i2c_check_msg_for_dma(msg, RCAR_DMA_THRESHOLD, NULL) == -EFAULT) {
> + dev_dbg(dev, "skipping DMA for this whole transfer\n");
Adding reason for skipping will be helpful.
> + priv->flags |= ID_P_NODMA;
> + }
>
> chan = read ? priv->dma_rx : priv->dma_tx;
> if (PTR_ERR(chan) != -EPROBE_DEFER)
> @@ -740,6 +746,8 @@ static int rcar_i2c_master_xfer(struct i2c_adapter *adap,
> if (ret < 0 && ret != -ENXIO)
> dev_err(dev, "error %d : %x\n", ret, priv->flags);
>
> + priv->flags &= ~ID_P_NODMA;
> +
> return ret;
> }
>
> --
> 2.11.0
>
thanks,
-- Shuah
