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Date: Tue, 2 Apr 2024 15:12:04 +0100
From: Sudeep Holla <sudeep.holla@arm.com>
To: "Mediouni, Mohamed" <mediou@amazon.de>
Cc: David Woodhouse <dwmw2@infradead.org>,
	"linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Sudeep Holla <sudeep.holla@arm.com>, Will Deacon <will@kernel.org>,
	Robert Moore <robert.moore@intel.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	Len Brown <lenb@kernel.org>, "Saidi, Ali" <alisaidi@amazon.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	"acpica-devel@lists.linux.dev" <acpica-devel@lists.linux.dev>,
	Saket Dumbre <saket.dumbre@intel.com>
Subject: Re: [PATCH 2/2] arm64: acpi: Honour firmware_signature field of
 FACS, if it exists
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On Tue, Apr 02, 2024 at 12:17:22PM +0000, Mediouni, Mohamed wrote:
> 
> > On 2. Apr 2024, at 12:29, Sudeep Holla <sudeep.holla@arm.com> wrote:
> > 
> > I think it is OK as a temporary solution for now. But there was some
> > investigation last year as part of some work in Linaro to enable
> > "drivers/acpi/sleep.c" into the build cleaning up some x86-ness in there.
> > acpi_sleep_hibernate_setup() already does this but enabling sleep.c need
> > some careful investigation so that it doesn't break any existing arm64/x86
> > platforms and made need some wordings clarification in the ACPI spec.
> > Today system suspend work via psci std path bypassing the ACPI paths which
> > may not be ideal as none of the ACPI methods are honoured. Some arm64
> > platforms may implement them and expect to be executed in the future,
> > maybe ?
> Current Windows on Arm platforms (seen on SC8280XP) don’t have _GTS
> or _PTS methods, and don’t have sleeping objects either.
>

IMO, SC8280XP is not a very good model platform for ACPI firmware reference.
It uses PEP which Linux doesn't support for good reason and that make it
hard to follow everything on that platform.

> As such, I don’t expect any users for that potential functionality.

I am not 100% sure

> Am I missing something or hibernation signalling to firmware (on ARM64)
> can be made PSCI only indefinitely?

Also bypassing certain operation taken care in sleep.c might result in
missing certain features. Few things IIRC(might be missing things myself
or misunderstood as it has been a while since I looked at the code in
detail): handing of GPE for wakeup, power resource handling during the
resume, power button event to mention few.

--
Regards,
Sudeep