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

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Message-ID: <20170311134119.GO3220@valkosipuli.retiisi.org.uk>
Date:   Sat, 11 Mar 2017 15:41:19 +0200
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Steve Longerbeam <slongerbeam@...il.com>
Cc:     robh+dt@...nel.org, mark.rutland@....com, shawnguo@...nel.org,
        kernel@...gutronix.de, fabio.estevam@....com,
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        Steve Longerbeam <steve_longerbeam@...tor.com>
Subject: Re: [PATCH v5 18/39] [media] v4l: subdev: Add function to validate
 frame interval

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@...tor.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.

-- 
Kind regards,

Sakari Ailus
e-mail: sakari.ailus@....fi	XMPP: sailus@...iisi.org.uk