Hi!

> > > In a Linux VM running on Hyper-V, when ACPI S4 is enabled, the balloon
> > > driver (drivers/hv/hv_balloon.c) needs to ask the host not to do memory
> > > hot-add/remove.
> > >
> > > So let's export acpi_sleep_state_supported() for the hv_balloon driver.
> > > This might also be useful to the other drivers in the future.
> > >
> > > Signed-off-by: Dexuan Cui <decui@microsoft.com>

> > 
> > It seems that sleep.c isn't built when on the ARM64 architecture.  Using
> > acpi_sleep_state_supported() directly in hv_balloon.c will be problematic
> > since hv_balloon.c needs to be architecture independent when the
> > Hyper-V ARM64 support is added.  If that doesn't change, a per-architecture
> > wrapper will be needed to give hv_balloon.c the correct information.  This
> > may affect whether acpi_sleep_state_supported() needs to be exported vs.
> > just removing the "static".   I'm not sure what the best approach is.
> > 
> > Michael
> 
> + some ARM experts who worked on arch/arm/kernel/hibernate.c.
> 
> drivers/acpi/sleep.c is only built if ACPI_SYSTEM_POWER_STATES_SUPPORT
> is defined, but it looks this option is not defined on ARM.
> 
> It looks ARM does not support the ACPI S4 state, then how do we know 
> if an ARM host supports hibernation or not?

You should be able to do hibernation without ACPI S4 support. All you
need is ability to powerdown...

It is well possible that noone tested hibernation on ARM.. people
usually do suspend-to-ram there.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
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