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

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Date:   Sat, 11 Mar 2017 12:31:24 -0800
From:   Steve Longerbeam <slongerbeam@...il.com>
To:     Sakari Ailus <sakari.ailus@....fi>
Cc:     robh+dt@...nel.org, mark.rutland@....com, shawnguo@...nel.org,
        kernel@...gutronix.de, fabio.estevam@....com,
        linux@...linux.org.uk, mchehab@...nel.org, hverkuil@...all.nl,
        nick@...anahar.org, markus.heiser@...marIT.de,
        p.zabel@...gutronix.de, laurent.pinchart+renesas@...asonboard.com,
        bparrot@...com, geert@...ux-m68k.org, arnd@...db.de,
        sudipm.mukherjee@...il.com, minghsiu.tsai@...iatek.com,
        tiffany.lin@...iatek.com, jean-christophe.trotin@...com,
        horms+renesas@...ge.net.au, niklas.soderlund+renesas@...natech.se,
        robert.jarzmik@...e.fr, songjun.wu@...rochip.com,
        andrew-ct.chen@...iatek.com, gregkh@...uxfoundation.org,
        shuah@...nel.org, sakari.ailus@...ux.intel.com, pavel@....cz,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org,
        devel@...verdev.osuosl.org,
        Steve Longerbeam <steve_longerbeam@...tor.com>
Subject: Re: [PATCH v5 18/39] [media] v4l: subdev: Add function to validate
 frame interval



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@...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.


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