linux-kernel - Re: [PATCH V2 1/2] clk: imx6: Add SPDIF

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Message-ID: <20150924115737.GM3529@tiger>
Date:	Thu, 24 Sep 2015 04:57:37 -0700
From:	Shawn Guo <shawnguo@...nel.org>
To:	Shengjiu Wang <shengjiu.wang@...escale.com>
Cc:	mturquette@...libre.com, kernel@...gutronix.de,
	sboyd@...eaurora.org, robh+dt@...nel.org, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, linux@....linux.org.uk,
	linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH V2 1/2] clk: imx6: Add SPDIF_GCLK clock in clock tree

On Thu, Sep 24, 2015 at 01:43:24PM +0800, Shengjiu Wang wrote:
> On Wed, Sep 23, 2015 at 08:33:41AM -0700, Shawn Guo wrote:
> > On Tue, Sep 15, 2015 at 06:01:01PM +0800, Shengjiu Wang wrote:
> > > As spdif driver will register SPDIF clock to regmap, regmap will do
> > > clk_prepare in init function, so SPDIF clock is prepared in probe, then its
> > > root clock (pll clock) is prepared also, which cause the arm can't enter
> > > low power mode.
> > 
> > Can you help me understand why ARM cannot enter low power mode when pll
> > clock is prepared?
> > 
> > Shawn
> Hi Shawn
> 
>    In i.mx clock framework, when pll clk is prepared, it will be powerup. when
> enterring low power idle mode, the powerdown bit is checked, when pll is not
> powerdown state, chip will not enter low power idle mode.

So this is not a SPDIF specific problem, and any device driver preparing
its clock that is a child of pll clock will run into this problem,
right?  If so, we should purchase a more generic solution than such
device specific one.

Shawn
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