On Mon, Jun 13, 2011 at 11:37 AM, Rafael J. Wysocki [off-list ref] wrote:

On Monday, June 13, 2011, Colin Cross wrote:

quoted

This patch set tries to address Russell's concerns with platform
pm code calling into the driver for every block in the Cortex A9s
during idle, hotplug, and suspend. ?The first patch adds cpu pm
notifiers that can be called by platform code, the second uses
the notifier to save and restore the GIC state, and the third
saves the VFP state.

The notifiers are used for two types of events, CPU PM events and
CPU complex PM events. ?CPU PM events are used to save and restore
per-cpu context when a single CPU is preparing to enter or has
just exited a low power state. ?For example, the VFP saves the
last thread context, and the GIC saves banked CPU registers.

CPU complex events are used after all the CPUs in a power domain
have been prepared for the low power state. ?The GIC uses these
events to save global register state.

Platforms that call the cpu_pm APIs must select
CONFIG_ARCH_USES_CPU_PM

L2 cache is not covered by this patch set, as the determination
of when the L2 is reset and when it is retained is
platform-specific, and most of the APIs necessary are already
present.

?arch/arm/Kconfig ? ? ? ? ? ? ?| ? ?7 ++
?arch/arm/common/gic.c ? ? ? ? | ?212 +++++++++++++++++++++++++++++++++++++++++
?arch/arm/include/asm/cpu_pm.h | ? 54 +++++++++++
?arch/arm/kernel/Makefile ? ? ?| ? ?1 +
?arch/arm/kernel/cpu_pm.c ? ? ?| ?181 +++++++++++++++++++++++++++++++++++

Is there any reason why this has to be ARM-specific? ?There are other
architectures where this kind of feature might make sense (SH and
powerpc at least).

Nothing other than there are currently no adaptations for any drivers
besides ARM, but I can move it somewhere outside ARM.  Any suggestions
where?

Besides, is there any overlap between this feature and the CPU hotplug
notifiers?

I don't think so - the hotplug notifiers are used when a CPU is being
removed from the system, so no saving and restoring is necessary - the
CPU will be rebooted from scratch.  They are used by systems outside
the CPU that need to know that a CPU no longer exists.

CPU PM notifiers are used when a CPU is going through reset in a way
that should be transparent to most of the system.  Only drivers within
the CPU itself need a notification.  Note that both ARM drivers I
modified did not have a register_cpu_notifier call.

Rafael