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

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Date:	Fri, 9 Oct 2015 17:15:30 +0800
From:	Shengjiu Wang <shengjiu.wang@...escale.com>
To:	Shawn Guo <shawnguo@...nel.org>
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 04:57:37AM -0700, Shawn Guo wrote:
> 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
Hi shawn

SPDIF_GCLK is also spdif's clock, it use a same enable bit with SPDIF_ROOT_CLK,
We didn't separate them in clock tree before.

I can't find a generic solution. But anyway if there is a solution or not, I
think we'd better to separate them.

best regards
wang shengjiu
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