linux-kernel - Re: [PATCH] ASoC: cs42888: Add codec driver support

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Date:	Tue, 25 Feb 2014 00:06:49 +0800
From:	Nicolin Chen <Guangyu.Chen@...escale.com>
To:	"Austin, Brian" <Brian.Austin@...rus.com>
CC:	Mark Brown <broonie@...nel.org>,
	"Handrigan, Paul" <Paul.Handrigan@...rus.com>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	"rob@...dley.net" <rob@...dley.net>,
	Liam Girdwood <lgirdwood@...il.com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>
Subject: Re: [PATCH] ASoC: cs42888: Add codec driver support

On Mon, Feb 24, 2014 at 03:52:24PM +0000, Austin, Brian wrote:
> >> +	if (!IS_ERR(cs42888->clk))
> >> +		clk_disable_unprepare(cs42888->clk);
> > 
> > Does the device work without MCLK?
> Yes, MCLK is required. If you can’t get the clock you should error out.

Wait...Regarding this clock part, I just forgot the reason I put the code:

385         cs42888->clk = devm_clk_get(&i2c->dev, "mclk");
386         if (IS_ERR(cs42888->clk))
387                 dev_warn(&i2c->dev, "failed to get the clock: %ld\n",
388                                 PTR_ERR(cs42888->clk));

was because the MCLK might be provided from SoC (DAI master) so it could
be totally controlled by CPU DAI driver, ESAI for example has its own
dividers to derive the HCKT clock (MCLK for Tx) from ahb clock in SoC
clock tree, in which case we might not easily pass a valid clock phandle
via DT. (RFC to this thought.)

Thank you,
Nicolin Chen


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