linux-kernel - Re: [PATCH 03/10] media: uvcvideo: Return -EIO for control errors

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Date:   Thu, 11 Mar 2021 22:56:22 +0100
From:   Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Ricardo Ribalda <ribalda@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Tomasz Figa <tfiga@...omium.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>
Subject: Re: [PATCH 03/10] media: uvcvideo: Return -EIO for control errors

Hi Laurent

On Thu, Mar 11, 2021 at 4:59 PM Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> Hi Ricardo,
>
> Thank you for the patch.
>
> On Thu, Mar 11, 2021 at 03:08:22PM +0100, Ricardo Ribalda wrote:
> > As discussed in the IRC with Hans
> >
> > We need to specify in the commit message that this is most likely due
> > to hw error.
> >
> > On Thu, Mar 11, 2021 at 1:20 PM Ricardo Ribalda <ribalda@...omium.org> wrote:
> > >
> > > Fixes v4l2-compliance:
> > >
> > > Control ioctls (Input 0):
> > >                 fail: v4l2-test-controls.cpp(448): s_ctrl returned an error (22)
> > >         test VIDIOC_G/S_CTRL: FAIL
> > >                 fail: v4l2-test-controls.cpp(698): s_ext_ctrls returned an error (22)
> > >         test VIDIOC_G/S/TRY_EXT_CTRLS: FAIL
>
> As this isn't supposed to happen, how do you reproduce this ?

Just run v4l2-compliance in my notebook camera.

>
> > > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > > ---
> > >  drivers/media/usb/uvc/uvc_video.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> > > index f2f565281e63..5442e9be1c55 100644
> > > --- a/drivers/media/usb/uvc/uvc_video.c
> > > +++ b/drivers/media/usb/uvc/uvc_video.c
> > > @@ -113,7 +113,7 @@ int uvc_query_ctrl(struct uvc_device *dev, u8 query, u8 unit,
> > >         case 6: /* Invalid control */
> > >         case 7: /* Invalid Request */
>
> For cases 5-7 I think -EIO is fine, as the driver should really not call
> this function with an invalid unit, control or request. If it does, it's
> a bug in the driver (we can check the units and controls the device
> claims to support, and the requests are defined by the UVC
> specification), if it doesn't and the device still returns this error,
> it's a bug on the device side.
>
> > >         case 8: /* Invalid value within range */
>
> For this case, however, isn't it valid for a device to return an error
> if the control value isn't valid ? There's one particular code path I'm
> concerned about, uvc_ioctl_default(UVCIOC_CTRL_QUERY) ->
> uvc_xu_ctrl_query() -> uvc_query_ctrl(), where it could be useful for
> userspace to know that the value it sets isn't valid.
>

Will fix in v2

Thanks!

> > > -               return -EINVAL;
> > > +               return -EIO;
> > >         default: /* reserved or unknown */
> > >                 break;
> > >         }
>
> --
> Regards,
>
> Laurent Pinchart



-- 
Ricardo Ribalda