[alsa-devel] [PATCH v2 1/2] ASoC: dmaengine-pcm: Add support for querying DMA capabilities

Mark Brown broonie at kernel.org
Tue Oct 8 18:46:48 CEST 2013

On Tue, Oct 08, 2013 at 09:00:24PM +0530, Vinod Koul wrote:
> On Tue, Oct 08, 2013 at 06:13:56PM +0200, Lars-Peter Clausen wrote:

> > >And second question for Takakshi or Mark. I see that this value ends up in
> > >usermode, what is the intented usage of this?

> > I think it is supposed to help to calculate the audio delay, but I
> > don't think it is actually that widely used at the moment. And yes,
> > in order to make this more accurate we should probably add support
> > for incorporating also the fifo size of the DMA channel.

> But then why dont add to delay field, why report to usermode

It's only really useful if the buffer is large enough to start causing
an issue with A/V sync and similar - it's there to help account for
delays introduced after things have gone from DMA.  Most hardware has
relatively small buffers so it's not a big deal.  I don't know why the
two are expressed differently, though the fact that one is in units of
time and the other is in units of data suggests it's just about making
it easier to express.
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