Re: [PATCH v7 5/5] clk: dt: Introduce binding for critical clock support

Lee Jones
2015-07-27T07:31:55Z

On Mon, 27 Jul 2015, Maxime Ripard wrote:

> Hi Lee,
>
> On Wed, Jul 22, 2015 at 02:04:15PM +0100, Lee Jones wrote:
> > Signed-off-by: Lee Jones <lee.jones@linaro.org>
> > ---
> > .../devicetree/bindings/clock/clock-bindings.txt | 39 ++++++++++++++++++++++
> > 1 file changed, 39 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> > index 06fc6d5..4137034 100644
> > --- a/Documentation/devicetree/bindings/clock/clock-bindings.txt
> > +++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> > @@ -44,6 +44,45 @@ For example:
> > clocks by index. The names should reflect the clock output signal
> > names for the device.
> >
> > +critical-clock: Some hardware contains bunches of clocks which, in normal
> > + circumstances, 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, it is possible that some
> > + Operating Systems might attempt to disable them to save power.
> > + If this happens 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 'critical' 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.
> > +
> > + Expected values are hardware clock indices. If the
> > + clock-indices property (see below) is used, then supplied
> > + values must correspond to one of the listed identifiers.
> > + Using the clock-indices example below, hardware clock <2>
> > + is missing, therefore it is considered invalid to then
> > + list clock <2> as a critical clock.
>
> I think we should also consider having it simply as a boolean. Using
> indices for clocks that don't have any (for example because it only
> provides a single clock) seem to not really make much sense.

Then how would you distinguish between the clocks if the provider
provides more than a single clock?

> Also, since you can have a bunch of them, using critical-clocks seem
> more appropriate.

I can change the name to critical-clocks, no problem.

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