linux-kernel - RE: [PATCH 1/2] ASoC: da7218: Add bindings documentation for DA7218 audio codec

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Date:	Thu, 5 Nov 2015 17:59:29 +0000
From:	"Opensource [Adam Thomson]" <Adam.Thomson.Opensource@...semi.com>
To:	Mark Brown <broonie@...nel.org>,
	"Opensource [Adam Thomson]" <Adam.Thomson.Opensource@...semi.com>
CC:	Liam Girdwood <lgirdwood@...il.com>,
	Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Support Opensource" <Support.Opensource@...semi.com>
Subject: RE: [PATCH 1/2] ASoC: da7218: Add bindings documentation for DA7218
 audio codec

On November 05, 2015 14:59, Mark Brown wrote:

> > +- dlg,ldo-lvl : Required internal LDO voltage (mV) level
> > +	[<1050>, <1100>, <1200>, <1400>]
> 
> Why would this ever be anything other than the minimum voltage, and
> might we not want to vary it at runtime?

Normally you are correct and you'll want minimum voltage for the digital engine
but there may be the possibility for certain platform scenarios that to meet
timings a higher voltage is required. Would prefer to leave this in in case it
is required in the future. As a side, the default setting is the lowest voltage,
if this binding is not provided.

> 
> > +- dlg,biquad-cfg : List of data & address pairs to configure BiQuad filters
> > +	[ < {data1} {addr1} {data2} {addr2} ... >; ]
> > +- dlg,st-biquad-cfg : List of data & address pairs to configure Sidetone
> > +		      BiQuad filters
> > +	[ < {data1} {addr1} {data2} {addr2} ... >; ]
> 
> These look like DSP coefficients which I would therefore expect to be
> configurable at runtime via a binary control rather than specified in
> the DT - why are they in the DT?

The expectation was these would be set once and left for a platform, which is
why I added them to the DT. However there's no reason they couldn't be moved
to binary control. Having looked at other codecs, I assume SND_SOC_BYTES* would
be the preferred method for setting this kind of data?