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

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Message-ID: <CANiDSCtSKCn+mx8pGwuYCre9Wb7gONJYjLqc6tYLWQL3YXBmrw@mail.gmail.com>
Date: Mon, 2 Jun 2025 13:40:06 +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 13:24, Hans de Goede <hansg@...nel.org> wrote:
>
> On 2-Jun-25 13:11, Ricardo Ribalda wrote:
> > On Mon, 2 Jun 2025 at 13:07, Hans de Goede <hansg@...nel.org> wrote:
> >>
> >> Hi Ricardo,
> >>
> >> On 2-Jun-25 12:27, Ricardo Ribalda wrote:
> >>> 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?
> >>
> >> Ah yes I did miss that, sorry.
> >
> > My bad, I doubt it till the last second if I should split it or not :)
> >
> >>
> >> For the next time please split core changes out into their own
> >> separate patches.
> >>
> >> In this case I think the core changes are not necessary instead
> >> you can just do:
> >>
> >>         unsigned int converted_cmd = cmd;
> >>
> >> #ifdef CONFIG_COMPAT
> >>         converted_cmd = v4l2_compat_translate_cmd(cmd);
> >> #endif
> >
> > I believe this should work as well:
> >
> > unsigned int converted_cmd = cmd;
> > if (in_compat_syscall())
> >   converted_cmd = v4l2_compat_translate_cmd(cmd);
> >
> > the compiler knows that CONFIG_COMPAT=n means in_compat_syscall() will
> > be always fails.
> >
> > If it is ok with you (and it actually works :) ) I will use this version.
>
> I agree that that is cleaner/better and I also think it should work,
> so lets go with that.

Actually, v4l2_compat_translate_cmd() does not seem to be EXPORT_SYMBOL()ed

So I still need to do some changes in the core.
(It also does not handle COMPAT_32BIT_TIME... but in this case it
seems to be the same).


Any preference between what to use: v4l2_compat_translate_cmd() vs
video_translate_cmd()?

Thanks!
>
> Regards,
>
> Hans
>
>
>
> >>>> 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