linux-kernel - Re: [PATCH] media: cedrus: Forbid setting new formats on busy queues

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Date:   Thu, 14 Feb 2019 10:18:38 +0100
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Hans Verkuil <hverkuil@...all.nl>, linux-media@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...glegroups.com
Cc:     Maxime Ripard <maxime.ripard@...tlin.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH] media: cedrus: Forbid setting new formats on busy queues

Hi,

On Thu, 2019-02-14 at 09:59 +0100, Hans Verkuil wrote:
> On 2/14/19 9:37 AM, Paul Kocialkowski wrote:
> > Check that our queues are not busy before setting the format or return
> > EBUSY if that's the case. This ensures that our format can't change
> > once buffers are allocated for the queue.
> > 
> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> > ---
> >  drivers/staging/media/sunxi/cedrus/cedrus_video.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> > 
> > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_video.c b/drivers/staging/media/sunxi/cedrus/cedrus_video.c
> > index b5cc79389d67..3420a938a613 100644
> > --- a/drivers/staging/media/sunxi/cedrus/cedrus_video.c
> > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_video.c
> > @@ -282,8 +282,15 @@ static int cedrus_s_fmt_vid_cap(struct file *file, void *priv,
> >  {
> >  	struct cedrus_ctx *ctx = cedrus_file2ctx(file);
> >  	struct cedrus_dev *dev = ctx->dev;
> > +	struct vb2_queue *vq;
> >  	int ret;
> >  
> > +	vq = v4l2_m2m_get_vq(ctx->fh.m2m_ctx, f->type);
> > +	if (!vq)
> > +		return -EINVAL;
> 
> Can this ever happen?

I guess not, or something would be very wrong.
I have seen this check around when looking at how other drivers
implement this, but it does seem overkill.

Should I get rid of it in v2?

Cheers,

Paul

> Regards,
> 
> 	Hans
> 
> > +	else if (vb2_is_busy(vq))
> > +		return -EBUSY;
> > +
> >  	ret = cedrus_try_fmt_vid_cap(file, priv, f);
> >  	if (ret)
> >  		return ret;
> > @@ -299,8 +306,15 @@ static int cedrus_s_fmt_vid_out(struct file *file, void *priv,
> >  				struct v4l2_format *f)
> >  {
> >  	struct cedrus_ctx *ctx = cedrus_file2ctx(file);
> > +	struct vb2_queue *vq;
> >  	int ret;
> >  
> > +	vq = v4l2_m2m_get_vq(ctx->fh.m2m_ctx, f->type);
> > +	if (!vq)
> > +		return -EINVAL;
> > +	else if (vb2_is_busy(vq))
> > +		return -EBUSY;
> > +
> >  	ret = cedrus_try_fmt_vid_out(file, priv, f);
> >  	if (ret)
> >  		return ret;
> > 
-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com