linux-kernel - Re: [PATCH 0/3] Handling of reduced FPS in V4L2

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Message-ID: <ccea984f-c68a-b188-49fb-29f04b7a3382@synopsys.com>
Date:   Fri, 24 Mar 2017 11:52:08 +0000
From:   Jose Abreu <Jose.Abreu@...opsys.com>
To:     Hans Verkuil <hansverk@...co.com>,
        Jose Abreu <Jose.Abreu@...opsys.com>,
        <linux-media@...r.kernel.org>
CC:     Carlos Palminha <CARLOS.PALMINHA@...opsys.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] Handling of reduced FPS in V4L2

Hi Hans,

>> Can you please review this series, when possible? And if you
>> could test it on cobalt it would be great :)
> Hopefully next week. 

Thanks :)

> Did you have some real-world numbers w.r.t. measured
> pixelclock frequencies and 60 vs 59.94 Hz and 24 vs 23.976 Hz?

I did make some measurements but I'm afraid I didn't yet test
with many sources (I mostly tested with signal generators which
should have a higher precision clock than real sources). I have a
bunch of players here, I will test them as soon as I can.
Regarding precision: for our controller is theoretically and
effectively enough: The worst case is for 640x480, and even in
that case the difference between 60Hz and 59.94Hz is > 1 unit of
the measuring register. This still doesn't solve the problem of
having a bad source with a bad clock, but I don't know if we can
do much more about that.

>
> I do want to see that, since this patch series only makes sense if you can
> actually make use of it to reliably detect the difference.
>
> I will try to test that myself with cobalt, but almost certainly I won't
> be able to tell the difference; if memory serves it can't detect the freq
> with high enough precision.

Ok, thanks, this would be great because I didn't test the series
exactly "as is" because I'm using 4.10. I did look at vivid
driver but it already handles reduced frame rate, so it kind of
does what it is proposed in this series. If this helper is
integrated in the v4l2 core then I can send the patch to vivid.

Best regards,
Jose Miguel Abreu

>
> Regards,
>
> 	Hans