linux-kernel - Re: [PATCH 5/5] cpufreq: qcom-hw: Move driver initialisation earlier

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Message-ID: <20190917130522.GA31601@qperret.net>
Date:   Tue, 17 Sep 2019 15:05:22 +0200
From:   Quentin Perret <qperret@...rret.net>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Amit Kucheria <amit.kucheria@...aro.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        bjorn.andersson@...aro.org, edubezval@...il.com, agross@...nel.org,
        tdas@...eaurora.org, swboyd@...omium.org, ilina@...eaurora.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>, linux-pm@...r.kernel.org
Subject: Re: [PATCH 5/5] cpufreq: qcom-hw: Move driver initialisation earlier

Hi Daniel

On Tuesday 17 Sep 2019 at 14:47:22 (+0200), Daniel Lezcano wrote:
> 
> Hi Sudeep,
> 
> On 17/09/2019 11:34, Sudeep Holla wrote:
> > On Thu, Sep 12, 2019 at 04:02:34AM +0530, Amit Kucheria wrote:
> >> Allow qcom-hw driver to initialise right after the cpufreq and thermal
> >> subsystems are initialised in core_initcall so we get earlier access to
> >> thermal mitigation.
> >>
> >> Signed-off-by: Amit Kucheria <amit.kucheria@...aro.org>
> >> ---
> >>  drivers/cpufreq/qcom-cpufreq-hw.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/cpufreq/qcom-cpufreq-hw.c b/drivers/cpufreq/qcom-cpufreq-hw.c
> >> index 4b0b50403901..04676cc82ba6 100644
> >> --- a/drivers/cpufreq/qcom-cpufreq-hw.c
> >> +++ b/drivers/cpufreq/qcom-cpufreq-hw.c
> >> @@ -327,7 +327,7 @@ static int __init qcom_cpufreq_hw_init(void)
> >>  {
> >>  	return platform_driver_register(&qcom_cpufreq_hw_driver);
> >>  }
> >> -device_initcall(qcom_cpufreq_hw_init);
> >> +postcore_initcall(qcom_cpufreq_hw_init);
> > 
> > I am fine with core framework initcall pushed to earlier initcall levels
> > if required, but for individual/platform specific drivers I am not so
> > happy to see that.
> > 
> > This goes against the grand plan of single common kernel strategy by
> > Android moving all drivers as modules. We might decide to make this
> > a module. 
> 
> module = mounted file system = very late initialization
> 
> Is that the plan? Force every driver to load too late?
> 
> There are core drivers which must be loaded as soon as possible. If the
> qcom driver is one of them, then what is the problem?
> 
> "The grand plan" will have to solve this first before doing the module
> move.
> 
> > Also there are few cpufreq drivers that are modules. Will
> > they have issues ? If not, why do we need this change at all.
> 
> Because some boards don't have thermal issues with the cpufreq drivers
> as module, other boards have.
> 
> > Needing
> > thermal mitigation during boot this earlier is still too much of
> > expectation, I would rather boot slowly than relying on this feature.
> 
> And what if we want to boot faster? The boot time is one of a key point
> of benchmark.

Could you share test results for this ? It'd be nice to see what if
the gains in boot time outweight the additional pain for android folks
...

Thanks,
Quentin