linux-kernel - Re: [PATCH v3 4/5] ACPI / processor_idle : introduce ARCH_SUPPORTS_ACPI_PROCESSOR

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Date:	Tue, 16 Feb 2016 21:18:36 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Sudeep Holla <sudeep.holla@....com>
Cc:	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-ia64@...r.kernel.org, x86@...nel.org,
	Al Stone <al.stone@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Mahesh Sivasubramanian <msivasub@...eaurora.org>,
	Ashwin Chaugule <ashwin.chaugule@...aro.org>,
	Prashanth Prakash <pprakash@...eaurora.org>
Subject: Re: [PATCH v3 4/5] ACPI / processor_idle : introduce ARCH_SUPPORTS_ACPI_PROCESSOR_CSTATE

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