linux-kernel - Re: [PATCH 9/9] media: uvcvideo: Support granular power saving for compat syscalls

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Message-ID: <34d9f779-987f-4e2c-b046-5dc15641547c@kernel.org>
Date: Mon, 2 Jun 2025 12:10:59 +0200
From: Hans de Goede <hansg@...nel.org>
To: Ricardo Ribalda <ribalda@...omium.org>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Hans de Goede <hdegoede@...hat.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>, Hans Verkuil <hverkuil@...all.nl>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 9/9] media: uvcvideo: Support granular power saving for
 compat syscalls

Hi Ricardo,

On 28-May-25 19:58, Ricardo Ribalda wrote:
> Right now we cannot support granular power saving on compat syscalls
> because the VIDIOC_*32 NRs defines are not accessible to drivers.
> 
> Use the video_translate_cmd() helper to convert the compat syscall NRs
> into syscall NRs.
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/usb/uvc/uvc_v4l2.c     | 9 ++-------
>  drivers/media/v4l2-core/v4l2-ioctl.c | 3 ++-
>  include/media/v4l2-ioctl.h           | 1 +
>  3 files changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> index fcb1b79c214849ce4da96a86a688d777b32cc688..048ee7e01808c8944f9bd46e5df2931b9c146ad5 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -1282,15 +1282,10 @@ static long uvc_v4l2_pm_ioctl(struct file *file,
>  static long uvc_v4l2_unlocked_ioctl(struct file *file,
>  				    unsigned int cmd, unsigned long arg)
>  {
> -	/*
> -	 * For now, we do not support granular power saving for compat
> -	 * syscalls.
> -	 */
> -	if (in_compat_syscall())
> -		return uvc_v4l2_pm_ioctl(file, cmd, arg);
> +	unsigned int converted_cmd = video_translate_cmd(cmd);

It looks like something went wrong here and you did not test-compile this?
video_translate_cmd() is private to drivers/media/v4l2-core/v4l2-ioctl.c
so this should not compile.

You can use v4l2_compat_translate_cmd() but only when CONFIG_COMPAT is set
otherwise that symbol is not available.

Regards,

Hans



>  
>  	/* The following IOCTLs do need to turn on the camera. */
> -	switch (cmd) {
> +	switch (converted_cmd) {
>  	case UVCIOC_CTRL_QUERY:
>  	case VIDIOC_G_CTRL:
>  	case VIDIOC_G_EXT_CTRLS:
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 650dc1956f73d2f1943b56c42140c7b8d757259f..6fbd28f911cf23eec43ef1adcf64bd46ef067c81 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -3245,7 +3245,7 @@ static int check_array_args(unsigned int cmd, void *parg, size_t *array_size,
>  	return ret;
>  }
>  
> -static unsigned int video_translate_cmd(unsigned int cmd)
> +unsigned int video_translate_cmd(unsigned int cmd)
>  {
>  #if !defined(CONFIG_64BIT) && defined(CONFIG_COMPAT_32BIT_TIME)
>  	switch (cmd) {
> @@ -3266,6 +3266,7 @@ static unsigned int video_translate_cmd(unsigned int cmd)
>  
>  	return cmd;
>  }
> +EXPORT_SYMBOL(video_translate_cmd);
>  
>  static int video_get_user(void __user *arg, void *parg,
>  			  unsigned int real_cmd, unsigned int cmd,
> diff --git a/include/media/v4l2-ioctl.h b/include/media/v4l2-ioctl.h
> index c6ec87e88dfef9e6cfe1d1fb587c1600882fb14d..437b9f90714c62e0ba434ce47391ef64d88110aa 100644
> --- a/include/media/v4l2-ioctl.h
> +++ b/include/media/v4l2-ioctl.h
> @@ -687,6 +687,7 @@ int v4l2_compat_get_array_args(struct file *file, void *mbuf,
>  int v4l2_compat_put_array_args(struct file *file, void __user *user_ptr,
>  			       void *mbuf, size_t array_size,
>  			       unsigned int cmd, void *arg);
> +unsigned int video_translate_cmd(unsigned int cmd);
>  
>  /**
>   * typedef v4l2_kioctl - Typedef used to pass an ioctl handler.
>