Re: [PATCH] ACPI: PM: Export the function acpi_sleep_state_supported()

[Lorenzo Pieralisi]

On Fri, Jun 14, 2019 at 10:19:02PM +0000, Dexuan Cui wrote:
> > -----Original Message-----
> > From: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> > Sent: Friday, June 14, 2019 1:48 PM
> > To: Dexuan Cui <decui@xxxxxxxxxxxxx>; linux-acpi@xxxxxxxxxxxxxxx;
> > rjw@xxxxxxxxxxxxx; lenb@xxxxxxxxxx; robert.moore@xxxxxxxxx;
> > erik.schmauss@xxxxxxxxx
> > Cc: linux-hyperv@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; KY Srinivasan
> > <kys@xxxxxxxxxxxxx>; Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>;
> > Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>; Sasha Levin
> > <Alexander.Levin@xxxxxxxxxxxxx>; olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx;
> > jasowang@xxxxxxxxxx; vkuznets <vkuznets@xxxxxxxxxx>;
> > marcelo.cerri@xxxxxxxxxxxxx
> > Subject: RE: [PATCH] ACPI: PM: Export the function
> > acpi_sleep_state_supported()
> > 
> > From: Dexuan Cui <decui@xxxxxxxxxxxxx>  Sent: Friday, June 14, 2019 11:19
> > AM
> > >
> > > 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@xxxxxxxxxxxxx>
> > > ---
> > >  drivers/acpi/sleep.c    | 3 ++-
> > >  include/acpi/acpi_bus.h | 2 ++
> > >  2 files changed, 4 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/acpi/sleep.c b/drivers/acpi/sleep.c
> > > index a34deccd7317..69755411e008 100644
> > > --- a/drivers/acpi/sleep.c
> > > +++ b/drivers/acpi/sleep.c
> > > @@ -79,7 +79,7 @@ static int acpi_sleep_prepare(u32 acpi_state)
> > >  	return 0;
> > >  }
> > >
> > > -static bool acpi_sleep_state_supported(u8 sleep_state)
> > > +bool acpi_sleep_state_supported(u8 sleep_state)
> > >  {
> > >  	acpi_status status;
> > >  	u8 type_a, type_b;
> > > @@ -89,6 +89,7 @@ static bool acpi_sleep_state_supported(u8 sleep_state)
> > >  		|| (acpi_gbl_FADT.sleep_control.address
> > >  			&& acpi_gbl_FADT.sleep_status.address));
> > >  }
> > > +EXPORT_SYMBOL_GPL(acpi_sleep_state_supported);
> > >
> > >  #ifdef CONFIG_ACPI_SLEEP
> > >  static u32 acpi_target_sleep_state = ACPI_STATE_S0;
> > > diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
> > > index 31b6c87d6240..5b102e7bbf25 100644
> > > --- a/include/acpi/acpi_bus.h
> > > +++ b/include/acpi/acpi_bus.h
> > > @@ -651,6 +651,8 @@ static inline int acpi_pm_set_bridge_wakeup(struct
> > device *dev,
> > > bool enable)
> > >  }
> > >  #endif
> > >
> > > +bool acpi_sleep_state_supported(u8 sleep_state);
> > > +
> > >  #ifdef CONFIG_ACPI_SLEEP
> > >  u32 acpi_target_system_state(void);
> > >  #else
> > > --
> > > 2.19.1
> > 
> > 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?

Maybe we should start from understanding why you need to know whether
Hibernate is possible to answer your question ?

On ARM64 platforms system states are entered through PSCI firmware
interface that works for ACPI and device tree alike.

Lorenzo