From: "Mark A. Greer" <mgreer@animalcreek.com>
To: "Péter Ujfalusi" <peter.ujfalusi@ti.com>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>,
linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
Jarkko Nikula <jarkko.nikula@bitmer.com>
Subject: Re: [RFC] dmaengine: omap-dma: Allow DMA controller to prefetch data
Date: Mon, 5 Nov 2012 15:06:08 -0700 [thread overview]
Message-ID: <20121105220608.GE3062@animalcreek.com> (raw)
In-Reply-To: <50814B83.7090203@ti.com>
On Fri, Oct 19, 2012 at 02:45:55PM +0200, Péter Ujfalusi wrote:
> Hi,
>
> On 10/19/2012 01:33 AM, Russell King - ARM Linux wrote:
> > I would suggest getting some feedback from the ASoC people first, before
> > trying to invent new APIs to work around this stuff. If they can live
> > with having prefetch enabled on OMAP then there isn't an issue here. If
> > not, we need a solution to this.
> >
> > I do not believe that precisely stopping and starting playback across a
> > suspend/resume event is really necessary (it's desirable but the world
> > doesn't collapse if you miss a few samples.) It could be more of an
> > issue for pause/resume though, but as I say, that's for ASoC people to
> > comment on.
>
> There is another issue with the prefetch in audio:
> we tend to like to know the position of the DMA and also to know how much data
> we have stored in buffers, FIFOs. This information is used by userspace to do
> echo cancellation and also used by PA for example to do runtime mixing
> directly in the audio buffer. We have means to extract this information from
> McBSP for example (and from tlv320dac33 codec) but AFAIK this information can
> not be retrieved from sDMA.
> We could assume that the sDMA FIFO is kept full and report that as a 'delay'
> or do not account this information.
>
> For now I think the cyclic mode should not set the prefetch. If I recall right
> the cyclic mode is only used by audio at the moment.
>
> > I'm merely pointing out here that we need their feedback here before
> > deciding if there's anything further that needs to happen.
>
> Thanks Russell, I'll take a look at the implication of the prefetch for audio.
Ping?
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next prev parent reply other threads:[~2012-11-05 22:06 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-18 22:20 [RFC] dmaengine: omap-dma: Allow DMA controller to prefetch data Mark A. Greer
2012-10-18 22:46 ` Mark A. Greer
2012-10-18 22:55 ` Russell King - ARM Linux
2012-10-18 23:24 ` Mark A. Greer
2012-10-18 23:33 ` Russell King - ARM Linux
2012-10-18 23:50 ` Mark A. Greer
2012-10-19 12:45 ` Péter Ujfalusi
2012-11-05 22:06 ` Mark A. Greer [this message]
2012-11-16 22:39 ` Mark A. Greer
2012-11-17 11:31 ` Russell King - ARM Linux
2012-11-19 10:00 ` Peter Ujfalusi
2012-11-19 12:16 ` Russell King - ARM Linux
2012-11-19 10:01 ` Peter Ujfalusi
2012-11-19 16:19 ` Mark A. Greer
2012-11-19 16:49 ` Mark A. Greer
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