linux-kernel - Re: [PATCH -next] arm64: Export __cpu_logical

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Message-ID: <20200810101954.GA9480@gaia>
Date:   Mon, 10 Aug 2020 11:19:55 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Sumit Gupta <sumitg@...dia.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Will Deacon <will@...nel.org>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Hulk Robot <hulkci@...wei.com>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Bibek Basu <bbasu@...dia.com>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jon Hunter <jonathanh@...dia.com>
Subject: Re: [PATCH -next] arm64: Export __cpu_logical_map

On Mon, Aug 10, 2020 at 08:49:56AM +0100, Sudeep Holla wrote:
> On Sat, Aug 01, 2020 at 05:46:43PM +0530, Sumit Gupta wrote:
> > > > > > > ERROR: modpost: "__cpu_logical_map" [drivers/cpufreq/tegra194-cpufreq.ko] undefined!
> > > > > > >
> > > > > > > ARM64 tegra194-cpufreq driver use cpu_logical_map, export
> > > > > > > __cpu_logical_map to fix build issue.
> > > > > > >
> > > > >
> > > > > I wonder why like other instances in the drivers, the mpidr is not get
> > > > > directly from the cpu. The cpufreq_driver->init call happens when the cpu
> > > > > is being brought online and is executed on the required cpu IIUC.
> > > >
> > > > Yes, this occurs during hotplug case.
> > > > But in the case of system boot, 'cpufreq_driver->init' is called later
> > > > during cpufreq platform driver's probe. The value of CPU in 'policy->cpu'
> > > > can be different from the current CPU. That's why read_cpuid_mpidr() can't
> > > > be used.
> > >
> > > Fair enough, why not do cross call like in set_target ? Since it is one-off
> > > in init, I don't see any issue when you are doing it runtime for set_target.
> > >
> > > > > read_cpuid_mpidr() is inline and avoids having to export the logical_cpu_map.
> > > > > Though we may not add physical hotplug anytime soon, less dependency
> > > > > on this cpu_logical_map is better given that we can resolve this without
> > > > > the need to access the map.
> > >
> > > To be honest, we have tried to remove all the dependency on cluster id
> > > in generic code as it is not well defined. This one is tegra specific
> > > driver so should be fine. But I am still bit nervous to export
> > > cpu_logical_map as we have no clue what that would mean for physical
> > > hotplug.
> >
> > As suggested, I have done below change to get the cluster number using
> > read_cpuid_mpidr(). Please review and suggest if this looks ok?
> > I will send formal patch if the change is fine.
> >
> > diff --git a/drivers/cpufreq/tegra194-cpufreq.c
> > b/drivers/cpufreq/tegra194-cpufreq.c
> > index bae527e..06f5ccf 100644
> > --- a/drivers/cpufreq/tegra194-cpufreq.c
> > +++ b/drivers/cpufreq/tegra194-cpufreq.c
> > @@ -56,9 +56,11 @@ struct read_counters_work {
> >
> >  static struct workqueue_struct *read_counters_wq;
> >
> > -static enum cluster get_cpu_cluster(u8 cpu)
> > +static void get_cpu_cluster(void *cluster)
> >  {
> > -       return MPIDR_AFFINITY_LEVEL(cpu_logical_map(cpu), 1);
> > +       u64 mpidr = read_cpuid_mpidr() & MPIDR_HWID_BITMASK;
> > +
> > +       *((uint32_t *) cluster) = MPIDR_AFFINITY_LEVEL(mpidr, 1);
> >  }
> >
> >  /*
> > @@ -186,8 +188,10 @@ static unsigned int tegra194_get_speed(u32 cpu)
> >  static int tegra194_cpufreq_init(struct cpufreq_policy *policy)
> >  {
> >         struct tegra194_cpufreq_data *data = cpufreq_get_driver_data();
> > -       int cl = get_cpu_cluster(policy->cpu);
> >         u32 cpu;
> > +       u32 cl;
> > +
> > +       smp_call_function_single(policy->cpu, get_cpu_cluster, &cl, true);
> 
> Thanks for this, looks good to me. You can add:
> 
> Reviewed-by: Sudeep Holla <sudeep.holla@....com>

I already merged Kefeng's __cpu_logical_map fix (commit eaecca9e7710)
but if the above goes in, I can drop the EXPORT_SYMBOL part (and keep
the rest as it's a good refactoring).

-- 
Catalin