Subject: Re: [PATCH v5 18/39] [media] v4l: subdev: Add function to validate
 frame interval
To: Sakari Ailus <sakari.ailus@iki.fi>
References: <1489121599-23206-1-git-send-email-steve_longerbeam@mentor.com>
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 <20170311134119.GO3220@valkosipuli.retiisi.org.uk>
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        Steve Longerbeam <steve_longerbeam@mentor.com>
From: Steve Longerbeam <slongerbeam@gmail.com>
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Date: Sat, 11 Mar 2017 12:31:24 -0800
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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@mentor.com>
>
> 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