linux-kernel - Re: [PATCH 4/4] clk: dt: st: Introduce clock domain documentation

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Message-ID: <20150128075835.GF4567@x1>
Date:	Wed, 28 Jan 2015 07:58:35 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Mike Turquette <mturquette@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel@...inux.com, sboyd@...eaurora.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH 4/4] clk: dt: st: Introduce clock domain documentation

On Tue, 27 Jan 2015, Mike Turquette wrote:

> Quoting Lee Jones (2015-01-26 03:14:00)
> > Signed-off-by: Lee Jones <lee.jones@...aro.org>
> > ---
> >  .../devicetree/bindings/clock/st/st,clk-domain.txt | 34 ++++++++++++++++++++++
> >  1 file changed, 34 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/clock/st/st,clk-domain.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/clock/st/st,clk-domain.txt b/Documentation/devicetree/bindings/clock/st/st,clk-domain.txt
> > new file mode 100644
> > index 0000000..7309937
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/clock/st/st,clk-domain.txt
> > @@ -0,0 +1,34 @@
> > +STMicroelectronics Clock Domain
> > +
> > +ST hardware have a bunch of clocks which must not be turned off.
> > +If drivers a) fail to obtain a reference to any of these or b) give
> > +up a previously obtained reference during suspend, the common clk
> > +framework will attempt to turn them off and the hardware will
> > +subsequently die.  The only way to recover from this failure is to
> > +restart.
> > +
> > +To avoid either of these two scenarios from catastrophically
> > +disabling the running system we have implemented a clock domain
> > +where clocks are consumed and references are taken, thus preventing
> > +them from being shut down by the framework.
> > +
> > +We use the generic clock bindings found in:
> > +  Documentation/devicetree/bindings/clock/clock-bindings.txt
> > +
> > +Required properties:
> > +- compatible : Must be "st,clk-domain"
> 
> Seems like a useful feature for any clock provider, not just ST's. Have
> you thought about making this solution generic for DT-based clock
> providers?
> 
> We could amend the common clock binding to include a special "always on"
> clock group that is automagically prepared and enabled when the clock
> provider/driver is registered, using a common function.

OMG, I'm actually going to strangle you!

This is what I've been proposing to you (privately) for weeks.

Does this ring any bells?

  "Just FYI, I am not going to add any method to the kernel that
  permanently enables a clock via some new api. At the worst case your
  clock driver can simply call clk_prepare_enable in its probe
  function (there are some examples of this)."

I will be more than happy to make this a generic driver, if thats what
you want (now). ;)

> > +Example:
> > +
> > +clk-domain {
> > +       compatible = "st,clk-domain";
> > +       clocks = <&clk_s_c0_flexgen CLK_EXT2F_A9>,
> > +                <&clk_s_c0_flexgen CLK_COMPO_DVP>,
> > +                <&clk_s_c0_flexgen CLK_MMC_1>,
> > +                <&clk_s_c0_flexgen CLK_ICN_SBC>,
> > +                <&clk_s_c0_flexgen CLK_ICN_LMI>,
> > +                <&clk_s_c0_flexgen CLK_ICN_CPU>,
> > +                <&clk_s_c0_flexgen CLK_TX_ICN_DMU>,
> > +                <&clk_s_a0_flexgen CLK_IC_LMI0>,
> > +                <&clk_m_a9>;
> > +};

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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