linux-kernel - Re: [PATCH v2] ASoC: fsl_esai: Add ESAI CPU DAI driver

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Message-ID: <20140110165229.GP29039@sirena.org.uk>
Date:	Fri, 10 Jan 2014 16:52:29 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Nicolin Chen <Guangyu.Chen@...escale.com>
Cc:	timur@...i.org, alsa-devel@...a-project.org, robh+dt@...nel.org,
	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	rob@...dley.net, lgirdwood@...il.com, perex@...ex.cz,
	tiwai@...e.de, grant.likely@...aro.org, shawn.guo@...aro.org,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2] ASoC: fsl_esai: Add ESAI CPU DAI driver

On Fri, Jan 10, 2014 at 11:48:25PM +0800, Nicolin Chen wrote:

> I think I start to understand the point here: If a user only needs to playback
> the default case - 44.1KHz for example, the driver can just configure all the
> dividers once at the beginning, not every time, so that we can save further
> register overriding operation or even complicated clock selection and divisor
> calculation, which obviously makes the procedure clean and reduces the system
> loading even if it might be just in a slight level.

> Is this the reason, or maybe one of the reasons, to the defaults providing?

The main thing is that if the DAI driver does it then it's less code in
the machine drivers using it - what tends to happen otherwise is that
quite a few machine drivers end up replicating the same logic.  Hardware
designers tend to do a lot of cut'n'paste with these things so even if
the CODEC is different the clocking is often very similar.

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