[RFC PATCH 16/17] ARM: PM: enhance idle pm notifiers

[Colin Cross]

adding Rafael, since he was interested in cpu_pm notifiers.

On Thu, Jul 7, 2011 at 8:50 AM, Lorenzo Pieralisi
<lorenzo.pieralisi at arm.com> wrote:
> This patch adds notifiers to manage low-power entry/exit in a platform
> independent manner through a series of callbacks.
> The goal is to enhance CPU specific notifiers with a different notifier
> chain that executes callbacks defined to put the system into low-power
> states (C-state). The callback must be executed with IRQ disabled
> and caches still up and running, which in particular means that spinlocks
> implemented as ldrex/strex are still usable on ARM.
>
> The callbacks are a means to achieve common idle code, where the
> platform_pm_enter()/exit() functions trigger the actions required to
> enter/exit low-power states (PCU, clock tree and power domain
> programming) for a specific platform.
>
> Within the common idle code for ARM, the callbacks executed upon
> platform_pm_enter/exit run with a virtual mapping cloned from init_mm
> which means that the virtual address space is still accessible.
>
> The notifier is passed a (void *) argument, that in the context of
> common idle code is meant to define cpu and cluster states in order to allow
> the platform specific callback to handle power down/up actions accordingly.

Can you explain how this is different from the cpu_pm notifiers,
besides the name?  Would they get called at a different point in the
idle path?  Could they be the same notifier list as the cpu_pm
notifiers, but with different enum values?

If this is purely for platform idle ops, maybe something more like the
struct platform_suspend_ops would be more appropriate?

Rafael wanted cpu_pm moved to somewhere outside of ARM, but these
platform notifiers sound specific to an ARM common idle
implementation, in which case you might need to find another place to
put them besides cpu_pm.c.

> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
> ---
>  arch/arm/include/asm/cpu_pm.h |   15 +++++++
>  arch/arm/kernel/cpu_pm.c      |   92 +++++++++++++++++++++++++++++++++++++++--
>  2 files changed, 103 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm/include/asm/cpu_pm.h b/arch/arm/include/asm/cpu_pm.h
> index b4bb715..19b8106 100644
> --- a/arch/arm/include/asm/cpu_pm.h
> +++ b/arch/arm/include/asm/cpu_pm.h
> @@ -42,8 +42,21 @@ enum cpu_pm_event {

<snip>

>  int cpu_pm_register_notifier(struct notifier_block *nb);
>  int cpu_pm_unregister_notifier(struct notifier_block *nb);
> +int platform_pm_register_notifier(struct notifier_block *nb);
> +int platform__pm_unregister_notifier(struct notifier_block *nb);

Extra underscore

<snip>