Re: [PATCH] uvcvideo: improve error handling in uvc_query_ctrl()

[Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>]

Hi Hans

Thanks for the patch. I like how uvc is ending :)

On Mon, Mar 22, 2021 at 1:09 PM Hans Verkuil <hverkuil-cisco@xs4all.nl> wrote:
>
> - If __uvc_query_ctrl() failed with a non-EPIPE error, then
>   report that with dev_err. If an error code is obtained, then
>   report that with dev_dbg.
>
> - For error 2 (Wrong state) return -EACCES instead of -EILSEQ.
>   EACCES is a much more appropriate error code. EILSEQ will return
>   "Invalid or incomplete multibyte or wide character." in strerror(),
>   which is a *very* confusing message.
>
> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
> ---
> Ricardo, this too can be added to the uvc series.
> ---
>  drivers/media/usb/uvc/uvc_video.c | 44 +++++++++++++++++--------------
>  1 file changed, 24 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> index b63c073ec30e..3f461bb4eeb9 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -68,7 +68,7 @@ int uvc_query_ctrl(struct uvc_device *dev, u8 query, u8 unit,
>                         u8 intfnum, u8 cs, void *data, u16 size)
>  {
>         int ret;
> -       u8 error;
> +       u8 error = 0;
>         u8 tmp;
>
>         ret = __uvc_query_ctrl(dev, query, unit, intfnum, cs, data, size,
> @@ -76,35 +76,39 @@ int uvc_query_ctrl(struct uvc_device *dev, u8 query, u8 unit,
>         if (likely(ret == size))
>                 return 0;
>
> -       dev_dbg(&dev->udev->dev,
> -               "Failed to query (%s) UVC control %u on unit %u: %d (exp. %u).\n",
> -               uvc_query_name(query), cs, unit, ret, size);
> +       ret = ret < 0 ? ret : -EPIPE;
>
> -       if (ret != -EPIPE)
> -               return ret;
> -
> -       tmp = *(u8 *)data;
> +       if (ret == -EPIPE) {
> +               tmp = *(u8 *)data;
>
> -       ret = __uvc_query_ctrl(dev, UVC_GET_CUR, 0, intfnum,
> -                              UVC_VC_REQUEST_ERROR_CODE_CONTROL, data, 1,
> -                              UVC_CTRL_CONTROL_TIMEOUT);
> +               ret = __uvc_query_ctrl(dev, UVC_GET_CUR, 0, intfnum,
> +                                      UVC_VC_REQUEST_ERROR_CODE_CONTROL, data, 1,
> +                                      UVC_CTRL_CONTROL_TIMEOUT);
>
> -       error = *(u8 *)data;
> -       *(u8 *)data = tmp;
> +               if (ret == 1)
> +                       error = *(u8 *)data;
> +               *(u8 *)data = tmp;
> +               if (ret != 1)
> +                       ret = ret < 0 ? ret : -EPIPE;
> +       }
>
> -       if (ret != 1)
> -               return ret < 0 ? ret : -EPIPE;
> +       if (error)
> +               dev_dbg(&dev->udev->dev,
> +                       "Failed to query (%s) UVC control %u on unit %u: got error %u.\n",
> +                       uvc_query_name(query), cs, unit, error);
> +       else
> +               dev_err(&dev->udev->dev,
> +                       "Failed to query (%s) UVC control %u on unit %u: %d (exp. %u).\n",
> +                       uvc_query_name(query), cs, unit, ret, size);

If __uvc_query_ctrl and UVC_VC_REQUEST_ERROR_CODE_CONTROL failed,
error is 0. And I think that you want to show a dev_err in that case.
Maybe we can initialize error to 7 ?


>
> -       uvc_dbg(dev, CONTROL, "Control error %u\n", error);
> +       if (!error)
> +               return ret;
I think we do not want these two lines (read next comment)
>
>         switch (error) {
> -       case 0:
> -               /* Cannot happen - we received a STALL */
> -               return -EPIPE;
>         case 1: /* Not ready */
>                 return -EBUSY;
>         case 2: /* Wrong state */
> -               return -EILSEQ;
> +               return -EACCES;
>         case 3: /* Power */
>                 return -EREMOTE;
>         case 4: /* Out of range */

Maybe we want a dev_dbg if the error code is unknown and return ret?
> --
> 2.30.0
>


-- 
Ricardo Ribalda