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

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Message-ID: <f7cbf5ab-7564-4c81-84c9-b38b09e977f9@kernel.org>
Date: Mon, 8 Dec 2025 12:17:21 +0100
From: Hans de Goede <hansg@...nel.org>
To: Ricardo Ribalda <ribalda@...omium.org>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: 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,

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 loose 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.

Regards,

Hans