linux-kernel - Re: [RFC] [PATCH 3/3] ASoC: OMAP: Enhance OMAP1510 DMA progress software counter

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Date:	Mon, 10 Aug 2009 23:11:25 +0200
From:	Janusz Krzysztofik <jkrzyszt@....icnet.pl>
To:	Jarkko Nikula <jhnikula@...il.com>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Peter Ujfalusi <peter.ujfalusi@...ia.com>,
	Tony Lindgren <tony@...mide.com>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.arm.linux.org.uk" 
	<linux-arm-kernel@...ts.arm.linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] [PATCH 3/3] ASoC: OMAP: Enhance OMAP1510 DMA progress software counter

Monday 10 August 2009 11:43:25 Janusz Krzysztofik wrote:
> Monday 10 August 2009 10:50:06 Janusz Krzysztofik wrote:
> > Enhance period index accuracy, particularly just before buffer rewind, by
> > making use of DMA interrupt status flags in addition to simply counting
> > interrupts
>
> Sorry, this one is still buggy

To be clear: I meant only patch 3/3 was buggy, others seemed OK.

> an can break other OMAP models.

Overstatement.

> The bug hits when multiple interrupt flags are set in parallel.

Under heavy debugging, for the first time I have noticed several consecutive 
DMA interrupt requests with all three flags set alltogether: FRAME, LAST and 
BLOCK. It looks hopeless, doesn't it? Keeping the period index at 0 will not 
report any progress, other choices (increment, set max) will lead to buffer 
loss, right?

Anyway, that observation seems to prove the requirement for a more accurate 
period counter. Improving it should help under heavy load. I think it is 
worth of trying, even if there may be other corner cases still not addressed.

v2 of the patch will follow next.

Janusz
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