Re: [PATCH v4 29/36] media: imx: mipi-csi2: enable setting and getting of frame rates

[Steve Longerbeam]

On 02/18/2017 01:23 AM, Russell King - ARM Linux wrote:
> On Fri, Feb 17, 2017 at 05:12:44PM -0800, Steve Longerbeam wrote:
> > Hi Russell,
> >
> > I signed-off on this but after more review I'm not sure this is right.
> >
> > The CSI-2 receiver really has no control over frame rate. It's output
> > frame rate is the same as the rate that is delivered to it.
> >
> > So this subdev should either not implement these ops, or it should
> > refer them to the attached source subdev.
>
> Where in the V4L2 documentation does it say that is permissible?

https://www.linuxtv.org/downloads/v4l-dvb-apis-old/vidioc-subdev-g-frame-interval.html

"The frame interval only makes sense for sub-devices that can control 
the frame period on their own. This includes, for instance, image 
sensors and TV tuners. Sub-devices that don't support frame intervals 
must not implement these ioctls."


> If you don't implement these, media-ctl fails to propagate _anything_
> to the next sink pad if you specify a frame rate, because media-ctl
> throws an error and exits immediately.

But I agree with you here. I think our only option is to ignore that
quoted requirement above and propagate [gs]_frame_interval all the way
to the CSI (which can control the frame rate via frame skipping).

Steve