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 11:29:52 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        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 11:21 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 17-01-19, 11:08, Rafael J. Wysocki wrote:
> > On Thu, Jan 17, 2019 at 6:49 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > > 1. Have following for CONFIG_CPU_FREQ
> > >        depends on !CPU_THERMAL || THERMAL
> >
> > Sorry, but this makes my teeth hurt.
>
> I knew it :)
>
> > >    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'?
>
> That causes recursive-dependency issues:
>
> drivers/thermal/Kconfig:5:error: recursive dependency detected!
> drivers/thermal/Kconfig:5:      symbol THERMAL is selected by CPU_THERMAL
> drivers/thermal/Kconfig:16:     symbol CPU_THERMAL depends on THERMAL_OF
> drivers/thermal/Kconfig:70:     symbol THERMAL_OF depends on THERMAL
> For a resolution refer to Documentation/kbuild/kconfig-language.txt
> subsection "Kconfig recursive dependency limitations"
>
> something like this works though:
>
> diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
> index 30323426902e..ee9f9f2a795b 100644
> --- a/drivers/thermal/Kconfig
> +++ b/drivers/thermal/Kconfig
> @@ -13,6 +13,20 @@ menuconfig THERMAL
>           All platforms with ACPI thermal support can use this driver.
>           If you want this support, you should say Y or M here.
>
> +config CPU_THERMAL
> +       bool "generic cpu cooling support"
> +       depends on CPU_FREQ
> +       select THERMAL_OF
> +       select THERMAL
> +       help
> +         This implements the generic cpu cooling mechanism through frequency
> +         reduction. An ACPI version of this already exists
> +         (drivers/acpi/processor_thermal.c).
> +         This will be useful for platforms using the generic thermal interface
> +         and not the ACPI interface.
> +
> +         If you want this support, you should say Y here.
> +

My sort of educated guess is that it is under the "if THERMAL" so that
it doesn't show up at all when THERMAL is unset.

>  if THERMAL
>
>  config THERMAL_STATISTICS
> @@ -148,19 +162,6 @@ config THERMAL_GOV_POWER_ALLOCATOR
>           Enable this to manage platform thermals by dynamically
>           allocating and limiting power to devices.
>
> -config CPU_THERMAL
> -       bool "generic cpu cooling support"
> -       depends on CPU_FREQ

But what about adding

      depends on THERMAL=y

here as I said in the other message?

> -       depends on THERMAL_OF
> -       help
> -         This implements the generic cpu cooling mechanism through frequency
> -         reduction. An ACPI version of this already exists
> -         (drivers/acpi/processor_thermal.c).
> -         This will be useful for platforms using the generic thermal interface
> -         and not the ACPI interface.
> -
> -         If you want this support, you should say Y here.
> -
>  config CLOCK_THERMAL
>         bool "Generic clock cooling support"
>         depends on COMMON_CLK
>
>
> What about make CONFIG_THERMAL bool instead ? Who wants it to be a module ?
>
> $ git grep "CONFIG_THERMAL=m"
> arch/arm/configs/mini2440_defconfig:CONFIG_THERMAL=m
> arch/arm/configs/omap2plus_defconfig:CONFIG_THERMAL=m
> arch/arm/configs/pxa_defconfig:CONFIG_THERMAL=m
> arch/mips/configs/ip22_defconfig:CONFIG_THERMAL=m
> arch/mips/configs/ip27_defconfig:CONFIG_THERMAL=m
> arch/unicore32/configs/unicore32_defconfig:#CONFIG_THERMAL=m
>
> Not sure if they really want this code out :(

Me neither.