Re: [PATCH 2/2] em28xx: fix VBI handling logic

[Mauro Carvalho Chehab <mchehab@osg.samsung.com>]

Em Thu, 25 Sep 2014 15:59:12 +0200
Frank Schäfer <fschaefer.oss@googlemail.com> escreveu:

> 
> Am 24.09.2014 um 01:18 schrieb Mauro Carvalho Chehab:
> > Em Tue, 23 Sep 2014 21:32:02 +0200
> > Frank Schäfer <fschaefer.oss@googlemail.com> escreveu:
> >
> >> Am 19.09.2014 um 18:02 schrieb Mauro Carvalho Chehab:
> >>> When both VBI and video are streaming, and video stream is stopped,
> >>> a subsequent trial to restart it will fail, because S_FMT will
> >>> return -EBUSY.
> >>>
> >>> That prevents applications like zvbi to work properly.
> >>>
> >>> Please notice that, while this fix it fully for zvbi, the
> >>> best is to get rid of streaming_users and res_get logic as a hole.
> >>>
> >>> However, this single-line patch is better to be merged at -stable.
> >>>
> >>> Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
> >>>
> >>> diff --git a/drivers/media/usb/em28xx/em28xx-video.c b/drivers/media/usb/em28xx/em28xx-video.c
> >>> index 08569cbccd95..d75e7f82dfb9 100644
> >>> --- a/drivers/media/usb/em28xx/em28xx-video.c
> >>> +++ b/drivers/media/usb/em28xx/em28xx-video.c
> >>> @@ -1351,7 +1351,7 @@ static int vidioc_s_fmt_vid_cap(struct file *file, void *priv,
> >>>  	struct em28xx *dev = video_drvdata(file);
> >>>  	struct em28xx_v4l2 *v4l2 = dev->v4l2;
> >>>  
> >>> -	if (v4l2->streaming_users > 0)
> >>> +	if (vb2_is_busy(&v4l2->vb_vidq))
> >> Looks dangerous.
> > Why Dangerous? 
> You are an experienced kernel developer. If you still fail to see that
> after so many years, sorry, I can't help you.
> 
> > Did you identify any problem?
> Yes I've identified a potential problem.
> Read it again, it's in the line you skipped in this reply.

Did you read the video_ioctl_ops struct?

See:

	.vidioc_g_fmt_vid_cap       = vidioc_g_fmt_vid_cap,
	.vidioc_try_fmt_vid_cap     = vidioc_try_fmt_vid_cap,
	.vidioc_s_fmt_vid_cap       = vidioc_s_fmt_vid_cap,
	.vidioc_g_fmt_vbi_cap       = vidioc_g_fmt_vbi_cap,
	.vidioc_try_fmt_vbi_cap     = vidioc_g_fmt_vbi_cap,
	.vidioc_s_fmt_vbi_cap       = vidioc_g_fmt_vbi_cap,
	.vidioc_enum_framesizes     = vidioc_enum_framesizes,
	.vidioc_g_audio             = vidioc_g_audio,
	.vidioc_s_audio             = vidioc_s_audio,

Only the video node calls s_fmt_vid_cap. There's nothing to be
set for VBI. In other words, a call to VIDIOC_S_FMT will
actually call vidioc_g_fmt_vbi_cap() if called from VBI.

So, I was unable to see any potencial issues.

> > With what application?
> I would be willing to spend more time on this and test this critical
> patch (like I already did in the past).
> But I don't have access to analog TV here at the moment, sorry. It would
> have to wait ~2 weeks.

On my tests with the 3 existing VBI apps, they all worked fine
after the patch, no matter if the VBI or the video application
is started first.

That's why I asked.

Regards,
Mauro