On Tue, Mar 12, 2019 at 8:44 PM Wolfram Sang
<wsa+rene...@sang-engineering.com> 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 <hsi...@chromium.org>
> Fixes: e94bc5d18be0 ("i2c: add helpers to ease DMA handling")
> Signed-off-by: Wolfram Sang <wsa+rene...@sang-engineering.com>
Thanks!

Reviewed-by: Hsin-Yi Wang <hsi...@chromium.org>
> ---
>
> 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
>

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