linux-kernel - Re: [RFC PATCH] [media] coda: Use S_PARM to set nominal framerate for h.264 encoder

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Date:	Mon, 12 Jan 2015 16:35:59 +0100
From:	Philipp Zabel <p.zabel@...gutronix.de>
To:	Hans Verkuil <hverkuil@...all.nl>
Cc:	Kamil Debski <k.debski@...sung.com>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	Frédéric Sureau 
	<frederic.sureau@...alys.com>,
	Jean-Michel Hautbois <jean-michel.hautbois@...alys.com>,
	Nicolas Dufresne <nicolas.dufresne@...labora.com>
Subject: Re: [RFC PATCH] [media] coda: Use S_PARM to set nominal framerate
 for h.264 encoder

Hi Hans,

thank you for the comments!

Am Montag, den 12.01.2015, 16:03 +0100 schrieb Hans Verkuil:
> On 12/22/2014 05:00 PM, Philipp Zabel wrote:
> > The encoder needs to know the nominal framerate for the constant bitrate
> > control mechanism to work. Currently the only way to set the framerate is
> > by using VIDIOC_S_PARM on the output queue.
> > 
> > Signed-off-by: Philipp Zabel <p.zabel@...gutronix.de>
> > ---
> >  drivers/media/platform/coda/coda-common.c | 29 +++++++++++++++++++++++++++++
> >  1 file changed, 29 insertions(+)
> > 
> > diff --git a/drivers/media/platform/coda/coda-common.c b/drivers/media/platform/coda/coda-common.c
> > index 39330a7..63eb510 100644
> > --- a/drivers/media/platform/coda/coda-common.c
> > +++ b/drivers/media/platform/coda/coda-common.c
> > @@ -803,6 +803,32 @@ static int coda_decoder_cmd(struct file *file, void *fh,
> >  	return 0;
> >  }
> >  
> > +static int coda_g_parm(struct file *file, void *fh, struct v4l2_streamparm *a)
> > +{
> > +	struct coda_ctx *ctx = fh_to_ctx(fh);
> > +
> 
> If a->type != V4L2_BUF_TYPE_VIDEO_OUTPUT, then return -EINVAL.

If the decoder can retrieve the framerate from the stream, wouldn't it
make sense to allow G_PARM for a->type == V4L2_BUF_TYPE_VIDEO_CAPTURE ?

>  Ditto for s_parm.

Will do.

> > +	a->parm.output.timeperframe.denominator = 1;
> > +	a->parm.output.timeperframe.numerator = ctx->params.framerate;
> > +
> > +	return 0;
> > +}
> > +
> > +static int coda_s_parm(struct file *file, void *fh, struct v4l2_streamparm *a)
> > +{
> > +	struct coda_ctx *ctx = fh_to_ctx(fh);
> > +
> > +	if (a->type == V4L2_BUF_TYPE_VIDEO_OUTPUT &&
> > +	    a->parm.output.timeperframe.numerator != 0) {
> > +		ctx->params.framerate = a->parm.output.timeperframe.denominator
> > +				      / a->parm.output.timeperframe.numerator;
> 
> Hmm, what happens if the denominator is 1 and the numerator is 2?
> You probably want to clamp ctx->params.framerate to the range of allowed framerates.
> And at least ensure a framerate > 0.
> 
> Also check with v4l2_compliance! You'd have caught at least the missing a->type check.

Oh dear, I need to improve my v4l-utils update habits. I'll fix this
patch and resend it.

regards
Philipp

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