From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sudeep Holla Subject: Re: [PATCH v7 5/8] CPPC: Add a CPUFreq driver for use with CPPC Date: Tue, 21 Jul 2015 16:32:33 +0100 Message-ID: <55AE6611.9020808@arm.com> References: <55AD0411.4000603@arm.com> <3774934.MfIr66XDWO@vostro.rjw.lan> <55AE083E.80303@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from foss.arm.com ([217.140.101.70]:60527 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753084AbbGUPch (ORCPT ); Tue, 21 Jul 2015 11:32:37 -0400 In-Reply-To: Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: "Rafael J. Wysocki" Cc: Sudeep Holla , "Rafael J. Wysocki" , Ashwin Chaugule , "jaswinder.singh@linaro.org" , "linux-pm@vger.kernel.org" , "linux-acpi@vger.kernel.org" , "linaro-acpi@lists.linaro.org" , "patches@linaro.org" , "viresh.kumar@linaro.org" Hi Rafael, On 21/07/15 15:27, Rafael J. Wysocki wrote: > Hi Sudeep, > > On Tue, Jul 21, 2015 at 10:52 AM, Sudeep Holla wrote: >> >> >> On 20/07/15 23:07, Rafael J. Wysocki wrote: >>> >>> On Monday, July 20, 2015 03:22:09 PM Sudeep Holla wrote: >>>> >>>> >>>> On 09/07/15 19:04, Ashwin Chaugule wrote: >>>>> >>>>> This driver utilizes the methods introduced in the previous >>>>> patch - "ACPI: Introduce CPU performance controls using CPPC" >>>>> and enables usage with existing CPUFreq governors. >>>>> >>>>> Signed-off-by: Ashwin Chaugule >>>>> Reviewed-by: Al Stone >>>>> >>>>> --- >>>>> drivers/cpufreq/Kconfig.arm | 16 ++++ >>>>> drivers/cpufreq/Makefile | 2 + >>>>> drivers/cpufreq/cppc_cpufreq.c | 197 >>>>> +++++++++++++++++++++++++++++++++++++++++ >>>>> 3 files changed, 215 insertions(+) >>>>> create mode 100644 drivers/cpufreq/cppc_cpufreq.c >>>>> >>>>> diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm >>>>> index 4f3dbc8..578384d 100644 >>>>> --- a/drivers/cpufreq/Kconfig.arm >>>>> +++ b/drivers/cpufreq/Kconfig.arm >>>>> @@ -272,3 +272,19 @@ config ARM_PXA2xx_CPUFREQ >>>>> This add the CPUFreq driver support for Intel PXA2xx SOCs. >>>>> >>>>> If in doubt, say N. >>>>> + >>>>> +config ACPI_CPPC_CPUFREQ >>>>> + tristate "CPUFreq driver based on the ACPI CPPC spec" >>>>> + depends on ACPI_CPPC_LIB >>>>> + default n >>>>> + help >>>>> + This adds a CPUFreq driver which uses CPPC methods >>>>> + as described in the ACPIv5.1 spec. CPPC stands for >>>>> + Collaborative Processor Performance Controls. It >>>>> + is based on an abstract continuous scale of CPU >>>>> + performance values which allows the remote power >>>>> + processor to flexibly optimize for power and >>>>> + performance. CPPC relies on power management firmware >>>>> + for its operation. >>>> >>>> >>>> Why is this ARM specific ? It might be used only on ARM but doesn't mean >>>> it should be visible only on ARM ACPI systems. >>> >>> >>> Why bother people with considering Kconfig options that are useless to >>> them? >>> >> >> I agree to some extent, but main worry is that we are then making these >> features architecture specific while ACPI is supposed to be architecture >> agnostic. I was just trying to avoid doing so. > > Problem is, there are no plans to support CPPC on x86 in Linux I'm > aware of and so we should not use it even if it is exposed by the > firmware (Windows may be using it, though). > Ah that makes sense. > I'm also not aware of plans to support _PSS on ARM. Agreed, but you never know what ARM vendors can do :) > > So, even though on the spec level they are arch-independent, the way > we use those interfaces in the kernel isn't. > Understood. Regards, Sudeep