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Date: Fri, 12 Sep 2014 15:43:36 -0400
From: Jon Masters <jcm@redhat.com>
Organization: Red Hat, Inc.
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To: Hanjun Guo <hanjun.guo@linaro.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Mark Rutland <mark.rutland@arm.com>, Olof Johansson <olof@lixom.net>,
        Grant Likely <grant.likely@linaro.org>,
        Will Deacon <will.deacon@arm.com>
CC: Graeme Gregory <graeme.gregory@linaro.org>, Arnd Bergmann <arnd@arndb.de>,
        Sudeep Holla <Sudeep.Holla@arm.com>,
        Jason Cooper <jason@lakedaemon.net>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Mark Brown <broonie@kernel.org>, Rob Herring <robh@kernel.org>,
        Robert Richter <rric@kernel.org>, Lv Zheng <lv.zheng@intel.com>,
        Robert Moore <robert.moore@intel.com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
        Liviu Dudau <Liviu.Dudau@arm.com>,
        Randy Dunlap <rdunlap@infradead.org>, Charles.Garcia-Tobin@arm.com,
        linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, linaro-acpi@lists.linaro.org,
        Tomasz Nowicki <tomasz.nowicki@linaro.org>
Subject: Re: [PATCH v4 05/18] ARM64 / ACPI: Introduce sleep-arm.c
References: <1410530416-30200-1-git-send-email-hanjun.guo@linaro.org> <1410530416-30200-6-git-send-email-hanjun.guo@linaro.org>
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On 09/12/2014 10:00 AM, Hanjun Guo wrote:
> From: Graeme Gregory <graeme.gregory@linaro.org>
> 
> ACPI 5.1 does not currently support S states for ARM64 hardware but
> ACPI code will call acpi_target_system_state() for device power
> managment, so introduce sleep-arm.c to allow other drivers to function
> until S states are defined.

Aside: ACPI5.1 does define the Platform Communication Channel and CPC
(Collaborative Processor Performance Control). Some details need to be
fleshed out there for practical 64-bit ARMv8 server systems, but the
underpinnings and mechanisms are in place in the 5.1 specification that
can be built upon over time to achieve practical S-State equivalence.

Jon.