Re: [PATCH v6 4/4] clk: dt: Introduce binding for always-on clock support

From: Maxime Ripard
Date: Wed Apr 08 2015 - 03:44:46 EST

Hi Lee,

On Tue, Apr 07, 2015 at 07:43:59PM +0100, Lee Jones wrote:
> Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
> ---
> .../devicetree/bindings/clock/clock-bindings.txt | 38 ++++++++++++++++++++++
> 1 file changed, 38 insertions(+)
> diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> index 06fc6d5..daf3323 100644
> --- a/Documentation/devicetree/bindings/clock/clock-bindings.txt
> +++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> @@ -44,6 +44,44 @@ 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.

Isn't "clocksource" here way too similar to, I don't know, the
clocksource framework? Wouln't clock provider be better?

> +
> + 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.

Disregarding what's stated here, I'm pretty sure that this will
actually happen. Where do you place the cursor?

Should we create a new driver for our RAM controller, or do we want to
use clock-always-on?

Do we really want to enforce this if we ever gain a driver that would
actually be able to manage its clock (like do we want the CPU clock to
never *ever* be gated just because we don't have a cpuidle/hotplug
driver yet?)

Have you seen the numerous NAK on such approach Mike did?


Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering

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