Date: Fri, 17 Mar 2017 00:17:27 +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,
        mchehab@kernel.org, hverkuil@xs4all.nl, nick@shmanahar.org,
        markus.heiser@darmarIT.de, p.zabel@pengutronix.de,
        laurent.pinchart+renesas@ideasonboard.com, bparrot@ti.com,
        geert@linux-m68k.org, arnd@arndb.de, sudipm.mukherjee@gmail.com,
        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: <20170316221727.GJ10701@valkosipuli.retiisi.org.uk>
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On Sat, Mar 11, 2017 at 12:31:24PM -0800, Steve Longerbeam wrote:
> 
> 
> 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.

Agreed.

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