linux-kernel - Re: [PATCH v2 3/6] media: uvcvideo: Announce deprecation intentions for UVCIOC_CTRL

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Message-ID: <CANiDSCvr7VRw91-AuJ8JTuhsuJNcg5XqLVvgjJycmqOKMcf3fg@mail.gmail.com>
Date: Tue, 9 Dec 2025 07:41:39 +0100
From: Ricardo Ribalda <ribalda@...omium.org>
To: Hans de Goede <hansg@...nel.org>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
	Mauro Carvalho Chehab <mchehab@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-usb@...r.kernel.org
Subject: Re: [PATCH v2 3/6] media: uvcvideo: Announce deprecation intentions
 for UVCIOC_CTRL_MAP

Hi Hans


On Mon, 8 Dec 2025 at 20:17, Hans de Goede <hansg@...nel.org> wrote:
>
> Hi,
>
> On 19-Nov-25 8:37 PM, Ricardo Ribalda wrote:
> > The UVCIOC_CTRL_MAP lets userspace create a mapping for a custom
> > control.
> >
> > This mapping is usually created by the uvcdynctrl userspace utility. We
> > would like to get the mappings into the driver instead.
> >
> > Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > ---
> >  Documentation/userspace-api/media/drivers/uvcvideo.rst | 2 ++
> >  drivers/media/usb/uvc/uvc_v4l2.c                       | 4 ++++
> >  2 files changed, 6 insertions(+)
> >
> > diff --git a/Documentation/userspace-api/media/drivers/uvcvideo.rst b/Documentation/userspace-api/media/drivers/uvcvideo.rst
> > index dbb30ad389ae4d53bc734b4269ebea20ecdd7535..b09d2f8ba66ecde67f1e35fd77858a505ad44eb1 100644
> > --- a/Documentation/userspace-api/media/drivers/uvcvideo.rst
> > +++ b/Documentation/userspace-api/media/drivers/uvcvideo.rst
> > @@ -109,6 +109,8 @@ IOCTL reference
> >  UVCIOC_CTRL_MAP - Map a UVC control to a V4L2 control
> >  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >
> > +**This IOCTL is deprecated and will be eventually removed**
> > +
> >  Argument: struct uvc_xu_control_mapping
> >
> >  **Description**:
> > diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> > index 9e4a251eca88085a1b4e0e854370015855be92ee..03c64b5698bf4331fed8437fa6e9c726a07450bd 100644
> > --- a/drivers/media/usb/uvc/uvc_v4l2.c
> > +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> > @@ -1044,6 +1044,8 @@ static long uvc_ioctl_default(struct file *file, void *priv, bool valid_prio,
> >       switch (cmd) {
> >       /* Dynamic controls. */
> >       case UVCIOC_CTRL_MAP:
> > +             pr_warn_once("uvcvideo: " DEPRECATED
> > +                          "UVCIOC_CTRL_MAP ioctl will be eventually removed.\n");
> >               return uvc_ioctl_xu_ctrl_map(chain, arg);
> >
> >       case UVCIOC_CTRL_QUERY:
>
> Deprecating and then removing this is going to be a long slow process.
>
> I was thinking that rather then remove it we would keep accepting the ioctl but instead
> of calling uvc_ioctl_xu_ctrl_map() we would simply return 0. E.g. change the above to:
>
>         case UVCIOC_CTRL_MAP:
>                 pr_warn_once("uvcvideo: " DEPRECATED
>                              "UVCIOC_CTRL_MAP ioctl will eventually be ignored.\n");
>                 return uvc_ioctl_xu_ctrl_map(chain, arg);
>
> And then say in one year after a kernel with the above is released change it to:
>
>         case UVCIOC_CTRL_MAP:
>                 pr_warn_once("uvcvideo: " DEPRECATED
>                              "UVCIOC_CTRL_MAP ioctls are ignored.\n");
>                 return 0;
>
>
> I think removing it in 1 year is too soon, but ignoring it is ok. This does mean
> that people will lose the custom v4l2-ctrls for which patch 2/6 is not adding
> mappings into the driver in 1 year after a kernel with the warning is released...
>
> I'm not 100% sure about this plan, so please let me know what you think. For
> outright deprecation warning + full removal I think we need to wait at least
> 2 years after shipping a kernel with the deprecation warning.

Let me rephrase what you have written:

today:
pr_warn_once("uvcvideo: " DEPRECATED "UVCIOC_CTRL_MAP ioctl will be
eventually ignored.\n");
return uvc_ioctl_xu_ctrl_map(chain, arg);

in 1 year:
pr_warn_once("uvcvideo: " DEPRECATED "UVCIOC_CTRL_MAP ioctl is ignored.\n");
return 0;

in  2 years:
return -ENOIOCTLCMD;


Normally I would prefer not to lie to userspace (saying that the
mapping was done, but not doing it).

But in this case, UVCIOC_CTRL_MAP does not seem to be very widely used
(check previous email), so I do not think it really matters if we skip
the "1 year step" and just return -ENOIOCTLCMD in 2 years.

I leave it up to you to decide the deprecation steps.

Best regards!

>
> Regards,
>
> Hans
>
>


-- 
Ricardo Ribalda