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

[Ricardo Ribalda <ribalda@chromium.org>]

hi Hans

On Thu, Mar 25, 2021 at 1:18 PM Hans Verkuil <hverkuil-cisco@xs4all.nl> wrote:
>
> On 23/03/2021 16:25, Ricardo Ribalda Delgado wrote:
> > 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 ?
>
> I'm confused, if error == 0, then it does show dev_err.

My bad.

Ignore the message.

Can we write it as ?:

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);
 return ret;
}

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);



>
> >
> >
> >>
> >> -       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?
>
> Make sense.
>
> Regards,
>
>         Hans



-- 
Ricardo Ribalda