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

Maxime Ripard
2015-07-27T07:10:58Z

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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.

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

Maxime

--
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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