linux-kernel - Re: [PATCH v2 4/5] ACPI / processor_idle : introduce ARCH_SUPPORTS_ACPI_PROCESSOR

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Message-ID: <5603F509.1090307@arm.com>
Date:	Thu, 24 Sep 2015 14:05:13 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	Ashwin Chaugule <ashwin.chaugule@...aro.org>
Cc:	Sudeep Holla <sudeep.holla@....com>,
	linux acpi <linux-acpi@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	lkml <linux-kernel@...r.kernel.org>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>, Al Stone <al.stone@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Mahesh Sivasubramanian <msivasub@...eaurora.org>
Subject: Re: [PATCH v2 4/5] ACPI / processor_idle : introduce
 ARCH_SUPPORTS_ACPI_PROCESSOR_CSTATE



On 24/09/15 11:31, Ashwin Chaugule wrote:
> Hi Sudeep,
>
> On 16 September 2015 at 09:59, Sudeep Holla <sudeep.holla@....com> 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)
>>
>> This patch will help to extend the processor_idle module to support
>> LPI.
>>
>> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
>> Signed-off-by: Sudeep Holla <sudeep.holla@....com>

[...]

>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 7aef2d52daa0..173075c48df8 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -34,6 +34,7 @@ config X86
>>          select ARCH_MIGHT_HAVE_ACPI_PDC         if ACPI
>>          select ARCH_MIGHT_HAVE_PC_PARPORT
>>          select ARCH_MIGHT_HAVE_PC_SERIO
>> +       select ARCH_SUPPORTS_ACPI_PROCESSOR_CSTATE if ACPI
>>          select ARCH_SUPPORTS_ATOMIC_RMW
>>          select ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT
>>          select ARCH_SUPPORTS_INT128             if X86_64
>> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
>> index 5d1015c26ff4..1eb0b8a84a65 100644
>> --- a/drivers/acpi/Kconfig
>> +++ b/drivers/acpi/Kconfig
>> @@ -48,6 +48,9 @@ config ACPI_LEGACY_TABLES_LOOKUP
>>   config ARCH_MIGHT_HAVE_ACPI_PDC
>>          bool
>>
>> +config ARCH_SUPPORTS_ACPI_PROCESSOR_CSTATE
>> +       bool
>> +
>>   config ACPI_GENERIC_GSI
>>          bool
>>
>
> Can't this be auto selected under ACPI_PROCESSOR_IDLE if X86 || IA64
> instead?

It can be done. The idea was to have ACPI_PROCESSOR_IDLE selected on
both x86 and ARM64.

processor_idle driver will support both _CST and _LPI
1. to avoid some code duplication
2. for easy enabling of _LPI on x86 if needed in future

Regards,
Sudeep
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