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

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Message-ID: <CANiDSCtrG59QX-R0YcS+G9HmG5oE8LwiXdm_NKuCbNmHp8aeTQ@mail.gmail.com>
Date: Mon, 2 Jun 2025 12:27:50 +0200
From: Ricardo Ribalda <ribalda@...omium.org>
To: Hans de Goede <hansg@...nel.org>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>, Hans de Goede <hdegoede@...hat.com>, 
	Mauro Carvalho Chehab <mchehab@...nel.org>, Hans Verkuil <hverkuil@...all.nl>, 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 Hans

On Mon, 2 Jun 2025 at 12:11, Hans de Goede <hansg@...nel.org> wrote:
>
> 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.

Hmm... Actually I am pretty sure that I tested it on real hardware.

Did you miss the EXPORT_SYMBOL() on the patch?

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

I tried now without CONFIG_COMPAT and it built fine.

>
> 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.
> >
>


-- 
Ricardo Ribalda