Message-ID: <69885612-75ea-422c-ba13-07eaf4325005@kernel.org>
Date: Mon, 2 Jun 2025 13:24:34 +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

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.

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.
>>>>>
>>>>
>>>
>>>
>>
> 
> 

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