linux-kernel - RE: [PATCH] media: v4l2-fh: define v4l2

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Date:   Thu, 26 Mar 2020 18:13:53 +0900
From:   "Seungchul Kim" <sc377.kim@...sung.com>
To:     "'Hans Verkuil'" <hverkuil@...all.nl>, <mchehab@...nel.org>
Cc:     <linux-media@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <sc377.kim@...sung.com>
Subject: RE: [PATCH] media: v4l2-fh: define v4l2_fh struct regardless of
 condition

On 3/26/20 5:17 PM, Hans Verkuil wrote:
> On 3/26/20 3:30 AM, Seungchul Kim wrote:
> > On 3/25/20 5:54 PM, Hans Verkuil wrote:
> >> On 3/23/20 3:30 AM, Seungchul Kim wrote:
> >>> v4l2_fh struct define differently by CONFIG_V4L2_MEM2MEM_DEV.
> >>> If some vendors use CONFIG_V4L2_MEM2MEM_DEV by module, it can make
> >>> the mismatch of v4l2_fh sturct.
> >>>
> >>> By the mismatch, the following error occurs.
> >>> ===============================
> >>> [    7.533506] v4l2_mem2mem: disagrees about version of symbol
> >> video_devdata
> >>> [    7.533594] v4l2_mem2mem: Unknown symbol video_devdata (err -22)
> >>> [    7.535319] v4l2_mem2mem: disagrees about version of symbol
> >>> v4l2_event_pending
> >>> [    7.542532] v4l2_mem2mem: Unknown symbol v4l2_event_pending (err -22)
> >>> ===============================
> >>>
> >>> So v4l2_fh struct is modified to does not have dependency for
> >>> CONFIG_V4L2_MEM2MEM_DEV.
> >>>
> >>> Signed-off-by: Seungchul Kim <sc377.kim@...sung.com>
> >>> ---
> >>>  include/media/v4l2-fh.h | 2 --
> >>>  1 file changed, 2 deletions(-)
> >>>
> >>> diff --git a/include/media/v4l2-fh.h b/include/media/v4l2-fh.h index
> >>> 53b4dbb..b5b3e00 100644
> >>> --- a/include/media/v4l2-fh.h
> >>> +++ b/include/media/v4l2-fh.h
> >>> @@ -53,9 +53,7 @@ struct v4l2_fh {
> >>>  	unsigned int		navailable;
> >>>  	u32			sequence;
> >>>
> >>> -#if IS_ENABLED(CONFIG_V4L2_MEM2MEM_DEV)
> >>>  	struct v4l2_m2m_ctx	*m2m_ctx;
> >>> -#endif
> >>
> >> This is a good change, but please also remove the same #if from
> >> v4l2_ioctl_get_lock() in drivers/media/v4l2-core/v4l2-ioctl.c. That
> >> is now no longer needed there either and without removing that those
> >> vendor drivers would be using the wrong lock.
> >>
> >> Regards,
> >>
> >> 	Hans
> >
> > Thank you for your comment. I worried about the same thing with you.
> > But vfh->m2m_ctx on v4l2_ioctl_get_lock() is always null without
> > CONFIG_V4L2_MEM2MEM_DEV, because m2m_ctx of v4l2-fh is initialized
> > only in v4l2_mem2mem.c.
> > Therefore it doesn't have a problem using an wrong lock regardless of
> > modification, so I did not fix it.
> 
> It is: if your out-of-tree driver sets CONFIG_V4L2_MEM2MEM_DEV, then I
> assume it will set vfh->m2m_ctx, and so the v4l2 core should also return
> the right lock for that out-of-tree driver.
> 
> But in any case, if m2m_ctx is always part of v4l2-fh.h, then that #if in
> v4l2-ioctl.c has become pointless and should be removed in any case.
> 
> Regards,
> 
> 	Hans

I agree with you, so I will update a patch, soon