linux-kernel - Re: [PATCH v2 3/3] media: au0828 remove video and vbi buffer timeout work-around

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Date:	Mon, 12 Jan 2015 19:08:12 -0700
From:	Shuah Khan <shuahkh@....samsung.com>
To:	Hans Verkuil <hverkuil@...all.nl>, m.chehab@...sung.com,
	hans.verkuil@...co.com, dheitmueller@...nellabs.com,
	prabhakar.csengg@...il.com, sakari.ailus@...ux.intel.com,
	laurent.pinchart@...asonboard.com, ttmesterr@...il.com
CC:	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] media: au0828 remove video and vbi buffer timeout
 work-around

On 01/12/2015 07:10 AM, Hans Verkuil wrote:
> On 12/18/2014 05:20 PM, Shuah Khan wrote:
>> au0828 does video and vbi buffer timeout handling to prevent
>> applications such as tvtime from hanging by ensuring that the
>> video frames continue to be delivered even when the ITU-656
>> input isn't receiving any data. This work-around is complex
>> as it introduces set and clear tier code paths in start/stop
>> streaming, and close interfaces. After the vb2 conversion, the
>> timeout handling is introducing instability as well as feeding
>> too many blank green screens, resulting in degraded video quality.
> 
> Why would this result in degraded video quality? And which instability
> exactly?

What I noticed was that I was seeing a few too many green screens
and I had to re-tune xawtv when the timeout code is in place. My
thinking was that this timeout handling could be introducing blank
green frames when there is no need. However, I can't reproduce the
problem on 3.19-rc4 base which is what I am using to test the changes
to the patch series. Hence, I am not positive if the timeout code
indeed was doing anything bad.

> 
>> Without this timeout handling, both xawtv, and tvtime are working
>> well with good quality video.

I am seeing tvtime hangs.

> 
> Erm, tvtime without the recent 'tvtime: don't block indefinitely waiting
> for frames' patch will not work well with au0828 without the timeout code
> if there is no valid video data.
> 
> This should at minimum be mentioned in the commit log.

I will resend the patch with the updated commit log knowing full well
that it might not be accepted.

I do have to re-cut the patch after the changes to address your
comments on the vb2 conversion patch. It applies, with fuzz, so
I decided to re-cut the patch.

thanks,
-- Shuah

-- 
Shuah Khan
Sr. Linux Kernel Developer
Open Source Innovation Group
Samsung Research America (Silicon Valley)
shuahkh@....samsung.com | (970) 217-8978
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