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

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Message-ID: <b88a8847-6e19-4d5e-a847-5deee69ab7b4@kernel.org>
Date: Mon, 2 Jun 2025 13:07:10 +0200
From: Hans de Goede <hansg@...nel.org>
To: Ricardo Ribalda <ribalda@...omium.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 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.

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

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.
>>>
>>
> 
>