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

From: Steve Longerbeam
Date: Sat Feb 18 2017 - 12:29:48 EST

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?

"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).