linux-kernel - Re: [RFC 1/2] ASoC: dmaengine-pcm: Add support for querying DMA capabilities

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Message-ID: <20130716100357.GE22506@sirena.org.uk>
Date:	Tue, 16 Jul 2013 11:03:57 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Lars-Peter Clausen <lars@...afoo.de>
Cc:	Vinod Koul <vinod.koul@...el.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/2] ASoC: dmaengine-pcm: Add support for querying DMA
 capabilities

On Tue, Jul 16, 2013 at 11:07:07AM +0200, Lars-Peter Clausen wrote:

> I would assume that most of them don't express hardware limitations but
> rather are sensible lower limits which allow operation without
> over-/underruns. But that's something that doesn't necessarily depend on the

Yes, indeed.  Or just cut'n'pasted from some other driver without much
thought.

> DMA controller, but rather on the system as a whole, e.g. on a slower
> machine you'd typically set the limit higher so the CPU has a better chance
> to keep up. So this isn't something you'd want to set in the DMA controller
> driver. But I'm not sure if there is a good way to calculate a sensible
> minimum buffer size based on the whole system's constraints.

Not really.  It's going to depend on userspace as well, and things like
SMIs on systems with those.

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