Re: [PATCH v5 4/4] clk: dt: Introduce binding for always-on clock support

Lee Jones
2015-04-07T09:42:31Z

On Thu, 02 Apr 2015, Geert Uytterhoeven wrote:

> On Wed, Apr 1, 2015 at 2:28 PM, Lee Jones <lee.jones@linaro.org> wrote:
> > Signed-off-by: Lee Jones <lee.jones@linaro.org>
> > ---
> > .../devicetree/bindings/clock/clock-bindings.txt | 31 ++++++++++++++++++++++
> > 1 file changed, 31 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> > index 06fc6d5..94cdda2 100644
> > --- a/Documentation/devicetree/bindings/clock/clock-bindings.txt
> > +++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> > @@ -44,6 +44,37 @@ For example:
> > clocks by index. The names should reflect the clock output signal
> > names for the device.
> >
> > +clock-always-on: Some hardware contains bunches of clocks which must never 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
> > + disable them and a platform can fail irrecoverably as a
> > + result. Usually the only way to recover from these failures
> > + is to reboot.
> > +
> > + To avoid either of these two scenarios from catastrophically
> > + disabling an otherwise perfectly healthy running system,
> > + clocks can be identified as always-on using this property
> > + from inside a clocksource's node.
> > +
> > + This property is not to be abused. It is only to be used to
> > + protect platforms from being crippled by gated clocks, not
> > + as a convenience function to avoid using the framework
> > + correctly inside device drivers.
>
> Please document what are the expected value(s) for this property.
> I assume these are clock indices into the array of hardware clocks?
>
> Do they take into account sparse hardware clocks, cfr. the "clock-indices"
> property below (I didn't check)?

They must match a valid indices. If the clock-indices property is
present, the value identified as always-on must match one of the
clocks listed.

I'll mention that.

> > +For example:
> > +
> > + oscillator {
> > + #clock-cells = <1>;
> > + clock-output-names = "ckil", "ckih";
> > + clock-always-on = <0>, <1>;
> > + };
> > +
> > +- this node defines a device with two clock outputs, just as in the
> > + example above. The only difference being that 'ckil' and 'ckih'
> > + are now identified as an always-on clocks, so the framework will
> > + know to never attempt to gate them.
> > +
> > clock-indices: If the identifying number for the clocks in the node
> > is not linear from zero, then this allows the mapping of
> > identifiers into the clock-output-names array.
>
> Gr{oetje,eeting}s,
>
> Geert
>

--
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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