Date: Sat, 11 Mar 2017 15:41:19 +0200
From: Sakari Ailus <sakari.ailus@iki.fi>
To: Steve Longerbeam <slongerbeam@gmail.com>
Cc: robh+dt@kernel.org, mark.rutland@arm.com, shawnguo@kernel.org,
        kernel@pengutronix.de, fabio.estevam@nxp.com, linux@armlinux.org.uk,
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        markus.heiser@darmarIT.de, p.zabel@pengutronix.de,
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        minghsiu.tsai@mediatek.com, tiffany.lin@mediatek.com,
        jean-christophe.trotin@st.com, horms+renesas@verge.net.au,
        niklas.soderlund+renesas@ragnatech.se, robert.jarzmik@free.fr,
        songjun.wu@microchip.com, andrew-ct.chen@mediatek.com,
        gregkh@linuxfoundation.org, shuah@kernel.org,
        sakari.ailus@linux.intel.com, pavel@ucw.cz, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-media@vger.kernel.org, devel@driverdev.osuosl.org,
        Steve Longerbeam <steve_longerbeam@mentor.com>
Subject: Re: [PATCH v5 18/39] [media] v4l: subdev: Add function to validate
 frame interval
Message-ID: <20170311134119.GO3220@valkosipuli.retiisi.org.uk>
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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.

-- 
Kind regards,

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