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

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Message-ID: <20210201100502.xluaj5rpqosqsq7b@vireshk-i7>
Date:   Mon, 1 Feb 2021 15:35:02 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Dominik Brodowski <linux@...inikbrodowski.net>
Cc:     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@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-omap@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH] cpufreq: Remove CPUFREQ_STICKY flag

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 ?

-- 
viresh