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Date: Thu, 31 Oct 2024 12:16:16 +0000
From: Catalin Marinas <catalin.marinas@arm.com>
To: David Woodhouse <dwmw2@infradead.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>, Jonathan Corbet <corbet@lwn.net>,
	Marc Zyngier <maz@kernel.org>,
	Oliver Upton <oliver.upton@linux.dev>,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>, Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Pavel Machek <pavel@ucw.cz>, Len Brown <len.brown@intel.com>,
	Shuah Khan <shuah@kernel.org>, David Woodhouse <dwmw@amazon.co.uk>,
	kvm@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.linux.dev, linux-pm@vger.kernel.org,
	linux-kselftest@vger.kernel.org,
	Francesco Lavra <francescolavra.fl@gmail.com>,
	Miguel Luis <miguel.luis@oracle.com>
Subject: Re: [PATCH v6 6/6] arm64: Use SYSTEM_OFF2 PSCI call to power off for
 hibernate
Message-ID: <ZyN1EMPCjdX7zZSB@arm.com>
References: <20241019172459.2241939-1-dwmw2@infradead.org>
 <20241019172459.2241939-7-dwmw2@infradead.org>
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In-Reply-To: <20241019172459.2241939-7-dwmw2@infradead.org>

On Sat, Oct 19, 2024 at 06:15:47PM +0100, David Woodhouse wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
> 
> The PSCI v1.3 specification adds support for a SYSTEM_OFF2 function
> which is analogous to ACPI S4 state. This will allow hosting
> environments to determine that a guest is hibernated rather than just
> powered off, and handle that state appropriately on subsequent launches.
> 
> Since commit 60c0d45a7f7a ("efi/arm64: use UEFI for system reset and
> poweroff") the EFI shutdown method is deliberately preferred over PSCI
> or other methods. So register a SYS_OFF_MODE_POWER_OFF handler which
> *only* handles the hibernation, leaving the original PSCI SYSTEM_OFF as
> a last resort via the legacy pm_power_off function pointer.
> 
> The hibernation code already exports a system_entering_hibernation()
> function which is be used by the higher-priority handler to check for
> hibernation. That existing function just returns the value of a static
> boolean variable from hibernate.c, which was previously only set in the
> hibernation_platform_enter() code path. Set the same flag in the simpler
> code path around the call to kernel_power_off() too.
> 
> An alternative way to hook SYSTEM_OFF2 into the hibernation code would
> be to register a platform_hibernation_ops structure with an ->enter()
> method which makes the new SYSTEM_OFF2 call. But that would have the
> unwanted side-effect of making hibernation take a completely different
> code path in hibernation_platform_enter(), invoking a lot of special dpm
> callbacks.
> 
> Another option might be to add a new SYS_OFF_MODE_HIBERNATE mode, with
> fallback to SYS_OFF_MODE_POWER_OFF. Or to use the sys_off_data to
> indicate whether the power off is for hibernation.
> 
> But this version works and is relatively simple.
> 
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> Acked-by: Rafael J. Wysocki <rafael@kernel.org>

Acked-by: Catalin Marinas <catalin.marinas@arm.com>