linux-kernel - Re: [PATCH v1 00/10] cpufreq: Add flag to auto-register as cooling device

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Date:   Thu, 17 Jan 2019 11:08:38 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Amit Kucheria <amit.kucheria@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Eduardo Valentin <edubezval@...il.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Sudeep Holla <sudeep.holla@....com>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        "open list:CPU FREQUENCY DRIVERS" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v1 00/10] cpufreq: Add flag to auto-register as cooling device

On Thu, Jan 17, 2019 at 6:49 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 14-01-19, 22:04, Amit Kucheria wrote:
> > Add a flag to be used by cpufreq drivers to tell cpufreq core to
> > auto-register themselves as a thermal cooling device.
> >
> > There series converts over all the drivers except arm_big_little.c.
> > Tested on SDM845 with the qcom-cpufreq-hw driver. Only compile-tested the
> > others.
> >
> > Things needing fixing:
> >  - Look at how to detect that we're not in IKS mode in arm_big_little's
> >    .ready callback.
>
> is_bL_switching_enabled() lets you know if IKS is enabled or not.
> Set/clear flag conditionally before the cpufreq-driver is registered,
> based on the output of is_bL_switching_enabled().
>
> >  - The other pending issue is to fix allmodconfig that leaves us with
> >    CPU_FREQ=y and THERMAL=m (CPU_THERMAL=y). That leads to undefined
> >    references for functions defined in cpu_cooling.c
>
> Okay, that's a terrible thing and the solution looks to be rather
> difficult.
>
> For others who may not be aware of the issue here, currently the
> cpufreq drivers use helpers of cpu_cooling.c (CONFIG_CPU_THERMAL),
> which uses helpers of the thermal core (CONFIG_THERMAL).
> CONFIG_THERMAL is defined as tristate and CONFIG_CPU_THERMAL as bool
> in Kconfigs.

And CONFIG_CPU_THERMAL is defined under "if THERMAL".

> The cpufreq drivers using the cpu_cooling.c file have this in their
> Kconfig entry:
>
> # if CPU_THERMAL is on and THERMAL=m, ARM_BIT_LITTLE_CPUFREQ cannot be =y
> #       depends on !CPU_THERMAL || THERMAL
>
>
> This series now places the cpufreq core in place of the cpufreq driver
> and it messes up everything. It is not just about allmodconfig, but
> any configuration which makes the compilation fail.
>
> What are the solutions we have now ?
>
> 1. Have following for CONFIG_CPU_FREQ
>        depends on !CPU_THERMAL || THERMAL

Sorry, but this makes my teeth hurt.

>    The platforms which don't need CPU_THERMAL (like x86) should not
>    enable CPU_THERMAL anymore if they want CONFIG_THERMAL=m.
>
>    @amit: If this gets accepted, please update the Kconfig entries for
>    all those drivers to not have above lines anymore.
>
> - Change CONFIG_THERMAL to bool instead of tristate ?
>
> - Anything else ?

The design in the thermal subsystem seems to be upside-down.
Non-modular code should never be made depend on anything only defined
in a module.

Would an explicit "select THERMAL" under CPU_THERMAL cause THERMAL to be 'y'?