linux-kernel - Re: [PATCH V2] ASoC: SAMSUNG: Add sound card driver for Snow board

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Date:	Thu, 1 May 2014 08:54:14 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Mark Brown <broonie@...nel.org>
Cc:	Tushar Behera <tushar.behera@...aro.org>,
	alsa-devel@...a-project.org,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-doc@...r.kernel.org,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Rob Herring <robh+dt@...nel.org>, sbkim73@...sung.com,
	Randy Dunlap <rdunlap@...radead.org>,
	Mike Turquette <mturquette@...aro.org>
Subject: Re: [PATCH V2] ASoC: SAMSUNG: Add sound card driver for Snow board

Hi,

On Thu, May 1, 2014 at 7:15 AM, Mark Brown <broonie@...nel.org> wrote:
> On Thu, May 01, 2014 at 04:59:08PM +0530, Tushar Behera wrote:
>
>> Okay, I will extend the existing clock driver to support XCLKOUT.
>
> It may make more sense to add another clock driver for this clock
> depending on how things are done, I don't know.
>
>> Of the many parents of XCLKOUT, we need to set XXTI clock as the parent.
>> Is it okay if we pass two clocks "mclk" (XCLKOUT) and "mclk_parent"
>> (XXTI) to sound-card driver via DT and do the necessary reparenting
>> during the sound-card driver probe call?
>
> No, that's not OK at all, it won't allow for configuration of the
> system.  This is what I was talking about when I was talking the clock
> framework extensions to allow the clock tree to be configured using DT,
> that would allow the settings to be put in DT.
>
>> Else, we can push that change to bootloader (to set the XCLKOUT mux
>> register) and only enable/disable the clock in sound-card driver.
>
> That's not going to work given that the existing bootloaders don't do
> this.

This is exactly the thing (expected clock parenting) we agreed could
be put in the device tree I think.  ...but I don't know that anyone
proposed exactly how that would work.

NOTE: in existing ChromeOS this type of thing is done a tiny amount in
<https://chromium.googlesource.com/chromiumos/third_party/kernel-next/+/chromeos-3.8/arch/arm/mach-exynos/mach-exynos5-dt.c>.
 See apply_clock_muxing().

-Doug
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