linux-kernel - RE: [RFC PATCH] cpufreq: add support for HiSilicon SoC HIP09

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Date:   Wed, 6 May 2020 14:57:07 +0000
From:   Souvik Chakravarty <Souvik.Chakravarty@....com>
To:     Thanu Rangarajan <Thanu.Rangarajan@....com>,
        Sudeep Holla <Sudeep.Holla@....com>,
        "guohanjun@...wei.com" <guohanjun@...wei.com>
CC:     Xiongfeng Wang <wangxiongfeng2@...wei.com>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "john.garry@...wei.com" <john.garry@...wei.com>,
        Jonathan Cameron <jonathan.cameron@...wei.com>
Subject: RE: [RFC PATCH] cpufreq: add support for HiSilicon SoC HIP09

Hi,

> From: Thanu Rangarajan <Thanu.Rangarajan@....com>
> Sent: Wednesday, May 6, 2020 1:58 PM
>
> Hi,
> ACPI CPPC already supports the notion of boost. Not sure we need any
> enhancements there.
>
> Regards,
> Thanu
>
> On 06/05/2020, 18:19, "Sudeep Holla" <sudeep.holla@....com> wrote:
>
>     + Thanu, Souvik who work with ASWG
>
>     On Wed, May 06, 2020 at 05:36:51PM +0800, Hanjun Guo wrote:
>     > Hi Sudeep,
>     >
>     > On 2020/4/30 17:55, Sudeep Holla wrote:
>     > > On Thu, Apr 30, 2020 at 02:19:59PM +0800, Xiongfeng Wang wrote:
>     > > > HiSilicon SoC has a separate System Control Processor(SCP)
> dedicated for
>     > > > clock frequency adjustment and has been using the cpufreq driver
>     > > > 'cppc-cpufreq'. New HiSilicon SoC HIP09 add support for CPU Boost,
> but
>     > > > ACPI CPPC doesn't support this. In HiSilicon SoC HIP09, each core has
>     > > > its own clock domain. It is better for the core itself to adjust its
>     > > > frequency when we require fast response. In this patch, we add a
>     > > > separate cpufreq driver for HiSilicon SoC HIP09.
>     > > >
>     > >
>     > > I disagree with this approach unless you have tried to extend the CPPC
>     > > in ACPI to accommodate this boost feature you need. Until you show
> those
>     > > efforts and disagreement to do that from ASWG, I am NACKing this
> approach.
>     >
>     > Unfortunately we are not in ASWG at now, could you please give some
>     > help about extending CPPC in ACPI to support boost feature?
>     >
>
>     You may have to provide more details than the commit log for sure as I
>     haven't understood the boost feature and what is missing in ACPI CPPC.

I would agree with Thanu here regarding the ACPI spec part - everything is already there.

It seems to me that the .set_boost is today not handled in cppc_cpufreq.c. In fact if a platform provides a value for Highest Performance which is different than Nominal Performance, then the entire range of performance is always requested, which works well for platforms which do boost enable/disable selection at hardware/firmware level.

.boost hook could potentially be useful in cppc_cpufreq.c for platforms which would manage the boost selection in software. But it would be good to keep a common implementation which can choose between "software-triggered or auto-boost" selection for different platforms.

Regards,
Souvik

>
>     --
>     Regards,
>     Sudeep
>
>

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