linux-kernel - Re: [PATCH 11/13] arm64: dts: qcom: qcs404: Add CPR and populate OPP table

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Date:   Fri, 19 Jul 2019 17:45:58 +0200
From:   Niklas Cassel <niklas.cassel@...aro.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Andy Gross <agross@...nel.org>, linux-arm-msm@...r.kernel.org,
        jorge.ramirez-ortiz@...aro.org, sboyd@...nel.org,
        vireshk@...nel.org, bjorn.andersson@...aro.org,
        ulf.hansson@...aro.org, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 11/13] arm64: dts: qcom: qcs404: Add CPR and populate OPP
 table

On Wed, Jul 17, 2019 at 10:19:23AM +0530, Viresh Kumar wrote:
> On 16-07-19, 12:53, Niklas Cassel wrote:
> > Here I cheated and simply used get_cpu_device(0).
> > 
> > Since I cheated, I used get_cpu_device(0) always,
> > so even when CPU1,CPU2,CPU3 is attached, dev_pm_opp_get_opp_count(cpu0) is
> > still 0.
> > 
> > I added a print in
> > [    3.836533] cpr_set_performance: number of OPPs for dev: cpu0: 3
> > 
> > And there I can see that OPP count is 3, so it appears that with the
> > current code, we need to wait until cpufreq-dt.c:cpufreq_init()
> > has been called, maybe dev_pm_opp_of_cpumask_add_table() needs
> > to be called before dev_pm_opp_get_opp_count(cpu0) actually returns 3.
> > 
> > cpufreq_init() is called by platform_device_register_simple("cpufreq-dt", -1,
> >                                                           NULL, 0);
> > which is called after dev_pm_opp_attach_genpd().
> > 
> > What I don't understand is that dev_pm_opp_attach_genpd() actually returns
> > a OPP table. So why do we need to wait for dev_pm_opp_of_cpumask_add_table(),
> > before either dev_pm_opp_get_opp_count(cpu0) or
> > dev_pm_opp_get_opp_count(genpd_virtdev_for_cpu0) returns 3?
> 
> Ah, I see the problems now. No, cpufreq table can't be available at
> this point of time and we aren't going to change that. It is the right
> thing to do.
> 
> Now, even if the kernel isn't written in a way which works for you, it
> isn't right to put more things in DT than required. DT is (should be)
> very much independent of the Linux kernel.
> 
> So we have to parse DT to find highest frequency for each
> required-opp. Best is to put that code in the OPP core and use it from
> your driver.

Hello Viresh,

Could you please have a look at the last two patches here:
https://git.linaro.org/people/niklas.cassel/kernel.git/log/?h=cpr-opp-hz

If you like my proposal then I could send out the first patch (the one to
OPP core) as a real patch (with an improved commit message), and
incorporate the second patch into my CPR patch series when I send out a V2.


Kind regards,
Niklas