Re: [PATCH v5 18/39] [media] v4l: subdev: Add function to validate frame interval

[Steve Longerbeam]

On 03/11/2017 05:41 AM, Sakari Ailus wrote:
> Hi Steve,
>
> On Thu, Mar 09, 2017 at 08:52:58PM -0800, Steve Longerbeam wrote:
> > If the pads on both sides of a link specify a frame interval, then
> > those frame intervals should match. Create the exported function
> > v4l2_subdev_link_validate_frame_interval() to verify this. This
> > function can be called in a subdevice's media_entity_operations
> > or v4l2_subdev_pad_ops link_validate callbacks.
> >
> > Signed-off-by: Steve Longerbeam <steve_longerbeam@xxxxxxxxxx>
>
> If your only goal is to configure frame dropping on a sub-device, I suggest
> to implement s_frame_interval() on the pads of that sub-device only. The
> frames are then dropped according to the configured frame rates between the
> sink and source pads. Say, configuring sink for 1/30 s and source 1/15 would
> drop half of the incoming frames.
>
> Considering that supporting specific frame interval on most sub-devices adds
> no value or is not the interface through which it the frame rate configured,
> I think it is overkill to change the link validation to expect otherwise.


Well, while I think this function might still have validity in the 
future, I do agree with you that a subdev that has no control over
frame rate has no business implementing the get|set ops.

In the imx-media subdevs, the only one that can affect frame rate (via
frame skipping) is the CSI. So I'll go ahead and remove the
[gs]_frame_interval ops from the others. I can remove this patch as
a result.


Steve