linux-kernel - Re: [RFC V2 1/2] ASoC: img: Add binding document for Pistachio audio card

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Date:	Wed, 27 Jan 2016 16:00:57 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Damien Horsley <Damien.Horsley@...tec.com>
Cc:	alsa-devel@...a-project.org, 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>,
	Liam Girdwood <lgirdwood@...il.com>,
	Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	James Hartley <james.hartley@...tec.com>
Subject: Re: [RFC V2 1/2] ASoC: img: Add binding document for Pistachio audio
 card

On Wed, Jan 27, 2016 at 03:18:20PM +0000, Damien Horsley wrote:
> On 27/01/16 14:57, Mark Brown wrote:
> > On Tue, Jan 26, 2016 at 02:34:26PM +0000, Damien Horsley wrote:

> >> +  - clock-names : Includes the following entries:
> >> +        "audio_pll"  The audio PLL
> >> +        "i2s_mclk"   The i2s reference clock
> >> +                     Also connected to i2s_out_0_mclk output
> >> +        "dac_mclk"   Dac reference clock. Connected to i2s_dac_clk output

> > Why are these (especially the dac_mclk and i2s_mclk) properties of the
> > card and not of the drivers for the respective devices?

> Due to the shared nature of these clocks. Individual components cannot
> be responsible for controlling these as this could break configurations
> for other components that are sharing the clocks. Only the card driver
> has visibility of all of the components and their requirements.

You're talking about the code that decides what rates to set the clock
at, not where the properties are placed in the DT.

> i2s_mclk and dac_mclk can be used by both the i2s in and i2s out paths
> on some boards

Multiple devices can reference the same clock.

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