On Tue, Mar 12, 2019 at 8:44 PM Wolfram Sang
<wsa+renesas@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> Make sure we report 'no buffer' for 0-length messages. This can only
> happen if threshold is set to 0 which is kind of bogus but we should
> still handle this situation. Update the docs and add a debug message
> to educate callers of this function.
>
> Reported-by: Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx>
> Fixes: e94bc5d18be0 ("i2c: add helpers to ease DMA handling")
> Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
Thanks!
Reviewed-by: Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx>
> ---
>
> Changes since v1:
> * add debug print
> * update kernel doc
> * update commit message
>
> drivers/i2c/i2c-core-base.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index cb6c5cb0df0b..986e56cee44b 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -2258,7 +2258,8 @@ EXPORT_SYMBOL(i2c_put_adapter);
> /**
> * i2c_get_dma_safe_msg_buf() - get a DMA safe buffer for the given i2c_msg
> * @msg: the message to be checked
> - * @threshold: the minimum number of bytes for which using DMA makes sense
> + * @threshold: the minimum number of bytes for which using DMA makes sense.
> + * Should at least be 1.
> *
> * Return: NULL if a DMA safe buffer was not obtained. Use msg->buf with PIO.
> * Or a valid pointer to be used with DMA. After use, release it by
> @@ -2268,7 +2269,11 @@ EXPORT_SYMBOL(i2c_put_adapter);
> */
> u8 *i2c_get_dma_safe_msg_buf(struct i2c_msg *msg, unsigned int threshold)
> {
> - if (msg->len < threshold)
> + /* also skip 0-length msgs for bogus thresholds of 0 */
> + if (!threshold)
> + pr_debug("DMA buffer for addr=0x%02x with length 0 is bogus\n",
> + msg->addr);
> + if (msg->len < threshold || msg->len == 0)
> return NULL;
>
> if (msg->flags & I2C_M_DMA_SAFE)
> --
> 2.11.0
>
