linux-kernel - Re: [PATCH v4 1/2] media: uvcvideo: Support partial control reads

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Message-ID: <CANiDSCuZkeV7jTVbNhnty8bMszUkb6g9czJfwDvRUFMhNdFp2Q@mail.gmail.com>
Date: Tue, 26 Nov 2024 19:12:53 +0100
From: Ricardo Ribalda <ribalda@...omium.org>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Hans de Goede <hdegoede@...hat.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, linux-media@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Sakari Ailus <sakari.ailus@...ux.intel.com>, 
	stable@...r.kernel.org
Subject: Re: [PATCH v4 1/2] media: uvcvideo: Support partial control reads

On Tue, 26 Nov 2024 at 19:06, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> On Wed, Nov 20, 2024 at 03:26:19PM +0000, Ricardo Ribalda wrote:
> > Some cameras, like the ELMO MX-P3, do not return all the bytes
> > requested from a control if it can fit in less bytes.
> > Eg: Returning 0xab instead of 0x00ab.
> > usb 3-9: Failed to query (GET_DEF) UVC control 3 on unit 2: 1 (exp. 2).
> >
> > Extend the returned value from the camera and return it.
> >
> > Cc: stable@...r.kernel.org
> > Fixes: a763b9fb58be ("media: uvcvideo: Do not return positive errors in uvc_query_ctrl()")
> > Reviewed-by: Hans de Goede <hdegoede@...hat.com>
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > ---
> >  drivers/media/usb/uvc/uvc_video.c | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> > index cd9c29532fb0..482c4ceceaac 100644
> > --- a/drivers/media/usb/uvc/uvc_video.c
> > +++ b/drivers/media/usb/uvc/uvc_video.c
> > @@ -79,6 +79,22 @@ int uvc_query_ctrl(struct uvc_device *dev, u8 query, u8 unit,
> >       if (likely(ret == size))
> >               return 0;
> >
> > +     /*
> > +      * In UVC the data is usually represented in little-endian.
>
> I had a comment about this in the previous version, did you ignore it on
> purpose because you disagreed, or was it an oversight ?

I rephrased the comment. I added "usually" to make it clear that it
might not be the case for all the data types. Like composed or xu.
I also r/package/packet/

Did I miss another comment?

>
> > +      * Some devices return shorter USB control packets that expected if the
> > +      * returned value can fit in less bytes. Zero all the bytes that the
> > +      * device have not written.
>
> s/have/has/
>
> And if you meant to start a new paragraph here, a blank line is missing.
> Otherwise, no need to break the line before 80 columns.

The patch is already in the uvc tree. How do you want to handle this?

>
> > +      * We exclude UVC_GET_INFO from the quirk. UVC_GET_LEN does not need to
> > +      * be excluded because its size is always 1.
> > +      */
> > +     if (ret > 0 && query != UVC_GET_INFO) {
> > +             memset(data + ret, 0, size - ret);
> > +             dev_warn_once(&dev->udev->dev,
> > +                           "UVC non compliance: %s control %u on unit %u returned %d bytes when we expected %u.\n",
> > +                           uvc_query_name(query), cs, unit, ret, size);
> > +             return 0;
> > +     }
> > +
> >       if (ret != -EPIPE) {
> >               dev_err(&dev->udev->dev,
> >                       "Failed to query (%s) UVC control %u on unit %u: %d (exp. %u).\n",
>
> --
> Regards,
>
> Laurent Pinchart



-- 
Ricardo Ribalda