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    SubjectRe: [PATCH 0/3] CPU PM notifiers
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    On Mon, Jun 13, 2011 at 11:37 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
    > On Monday, June 13, 2011, Colin Cross wrote:
    >> 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
    >
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