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Date:   Fri, 14 Jun 2019 23:33:10 +0100
From:   Russell King - ARM Linux admin <linux@armlinux.org.uk>
To:     Dexuan Cui <decui@microsoft.com>
Cc:     Michael Kelley <mikelley@microsoft.com>,
        "linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
        "rjw@rjwysocki.net" <rjw@rjwysocki.net>,
        "lenb@kernel.org" <lenb@kernel.org>,
        "robert.moore@intel.com" <robert.moore@intel.com>,
        "erik.schmauss@intel.com" <erik.schmauss@intel.com>,
        Russ Dill <Russ.Dill@ti.com>,
        Sebastian Capella <sebastian.capella@linaro.org>,
        Pavel Machek <pavel@ucw.cz>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        KY Srinivasan <kys@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Sasha Levin <Alexander.Levin@microsoft.com>,
        "olaf@aepfle.de" <olaf@aepfle.de>,
        "apw@canonical.com" <apw@canonical.com>,
        "jasowang@redhat.com" <jasowang@redhat.com>,
        vkuznets <vkuznets@redhat.com>,
        "marcelo.cerri@canonical.com" <marcelo.cerri@canonical.com>
Subject: Re: [PATCH] ACPI: PM: Export the function
 acpi_sleep_state_supported()
Message-ID: <20190614223310.pwwoefu5qdvcuaiy@shell.armlinux.org.uk>
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Hi,

On Fri, Jun 14, 2019 at 10:19:02PM +0000, Dexuan Cui wrote:
> > -----Original Message-----
> > From: Michael Kelley <mikelley@microsoft.com>
> > Sent: Friday, June 14, 2019 1:48 PM
> > To: Dexuan Cui <decui@microsoft.com>; linux-acpi@vger.kernel.org;
> > rjw@rjwysocki.net; lenb@kernel.org; robert.moore@intel.com;
> > erik.schmauss@intel.com
> > Cc: linux-hyperv@vger.kernel.org; linux-kernel@vger.kernel.org; KY Srinivasan
> > <kys@microsoft.com>; Stephen Hemminger <sthemmin@microsoft.com>;
> > Haiyang Zhang <haiyangz@microsoft.com>; Sasha Levin
> > <Alexander.Levin@microsoft.com>; olaf@aepfle.de; apw@canonical.com;
> > jasowang@redhat.com; vkuznets <vkuznets@redhat.com>;
> > marcelo.cerri@canonical.com
> > Subject: RE: [PATCH] ACPI: PM: Export the function
> > acpi_sleep_state_supported()
> > 
> > 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?

Don't forget that Linux does not support ACPI on 32-bit ARM, which is
quite different from the situation on 64-bit ARM.

arch/arm/kernel/hibernate.c is only for 32-bit ARM, and is written with
the assumption that there is no interaction required with any firmware
to save state, and later restore state upon resuming.

Or am I missing something?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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