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

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Date:   Thu, 26 Mar 2020 11:30:19 +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>
Subject: RE: [PATCH] media: v4l2-fh: define v4l2_fh struct regardless of
 condition

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.

Regards,
	Seungchul Kim