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From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Sudeep Holla <sudeep.holla@arm.com>
Cc: linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-ia64@vger.kernel.org, x86@kernel.org,
        Al Stone <al.stone@linaro.org>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
        Mahesh Sivasubramanian <msivasub@codeaurora.org>,
        Ashwin Chaugule <ashwin.chaugule@linaro.org>,
        Prashanth Prakash <pprakash@codeaurora.org>
Subject: Re: [PATCH v3 4/5] ACPI / processor_idle : introduce ARCH_SUPPORTS_ACPI_PROCESSOR_CSTATE
Date: Tue, 16 Feb 2016 21:18:36 +0100
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On Wednesday, December 02, 2015 02:10:45 PM Sudeep Holla wrote:
> ACPI 6.0 adds a new method to specify the CPU idle states(C-states)
> called Low Power Idle(LPI) states. Since new architectures like ARM64
> use only LPIs, introduce ARCH_SUPPORTS_ACPI_PROCESSOR_CSTATE to
> encapsulate all the code supporting the old style C-states(_CST)

No.

The way it really should work is to check if the firmware supports LPI
(and what kind of it) and try to use _CST if LPI is not supported.

If LPI is supported by the firmware, use it if the LPI objects are
present as expected or fall back to using _CST otherwise.

This way it all should work without any new Kconfig options.

Thanks,
Rafael