linux-kernel - Re: [PATCH] cpufreq: Remove CPUFREQ

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Date:   Mon, 1 Feb 2021 15:02:06 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Dominik Brodowski <linux@...inikbrodowski.net>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Keguang Zhang <keguang.zhang@...il.com>,
        Kevin Hilman <khilman@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mips@...r.kernel.org,
        Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Samsung SoC <linux-samsung-soc@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC..." 
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH] cpufreq: Remove CPUFREQ_STICKY flag

On Mon, Feb 1, 2021 at 11:06 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 01-02-21, 10:44, Dominik Brodowski wrote:
> > IIRC, it was required on various ARM systems,[*] as CPUs were registered as
> > subsys_initcall(), while cpufreq used to be initialized only later, as an
>
> s/later/earlier ? arch happens before subsys not at least and that is
> the only way we can break cpufreq here, i.e. when the driver comes up
> before the CPUs are registered.
>
> > arch_initcall(). If the ordering is opposite now on all architectures (it
> > wasn't on ARM back then), we should be fine.
> >
> > [*] https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/arch/arm/mach-sa1100/cpu-sa1100.c?id=f59d3bbe35f6268d729f51be82af8325d62f20f5
>
> Thanks for your reply, it made me look at that aspect in some more
> detail to confirm I don't end up breaking anything. Unless I am making
> a mistake in reading the code, this is the code flow that we have
> right now:
>
> start_kernel()
> -> kernel_init()
>    -> kernel_init_freeable()
>       -> do_basic_setup()
>          -> driver_init()
>             -> cpu_dev_init()
>                -> subsys_system_register(for-CPUs)
>
>          -> do_initcalls()
>             -> register-cpufreq-driver from any level
>
> And so CPUs should always be there for a cpufreq driver.
>
> Makes sense ?

It does to me, but can you update the changelog, please?