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

Jose Abreu
2017-03-24T12:21:50Z

Hi Hans,

On 24-03-2017 12:12, Hans Verkuil wrote:
> On 03/24/17 12:52, Jose Abreu wrote:
>> 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 would really like to see a table with different sources sending
> these different framerates and the value that your HW detects.
>
> If there is an obvious and clear difference, then this feature makes
> sense. If it is all over the place, then I need to think about this
> some more.
>
> To be honest, I expect that you will see 'an obvious and clear'
> difference, but that is no more than a gut feeling at the moment and
> I would like to see some proper test results.

Ok, I will make a table. The test procedure will be like this:
- Measure pixel clock value using certified HDMI analyzer
- Measure pixel clock using our controller
- Compare the values obtained from analyzer, controller and
the values that the source is telling to send (the value
displayed in source menu for example [though, some of them may
not discriminate the exact frame rate, thats why analyzer should
be used also]).

Seems ok? I will need some time, something like a week because my
setup was "borrowed".

Best regards,
Jose Miguel Abreu

>
>>> 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.
> That would be nice to have in vivid.
>
> Regards,
>
> Hans
>