Re: [PATCH v1 2/3] cpufreq: CPPC: Add per_cpu efficiency_class

From: Marc Zyngier <maz@kernel.org>
To: Pierre Gondois <pierre.gondois@arm.com>
Cc: linux-kernel@vger.kernel.org, Ionela.Voinescu@arm.com,
	Lukasz.Luba@arm.com, Morten.Rasmussen@arm.com,
	Dietmar.Eggemann@arm.com, mka@chromium.org,
	daniel.lezcano@linaro.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Ard Biesheuvel <ardb@kernel.org>, Fuad Tabba <tabba@google.com>,
	Rob Herring <robh@kernel.org>,
	linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH v1 2/3] cpufreq: CPPC: Add per_cpu efficiency_class
Date: Thu, 17 Mar 2022 16:31:30 +0000	[thread overview]
Message-ID: <87o824y1zx.wl-maz@kernel.org> (raw)
In-Reply-To: <d8502879-104e-c1c9-d735-d9de5769da41@arm.com>

On Thu, 17 Mar 2022 16:07:01 +0000,
Pierre Gondois <pierre.gondois@arm.com> wrote:
> 
> >> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> >> index 27df5c1e6baa..56637cbea5d6 100644
> >> --- a/arch/arm64/kernel/smp.c
> >> +++ b/arch/arm64/kernel/smp.c
> >> @@ -512,6 +512,7 @@ struct acpi_madt_generic_interrupt
> >> *acpi_cpu_get_madt_gicc(int cpu)
> >>   {
> >>   	return &cpu_madt_gicc[cpu];
> >>   }
> >> +EXPORT_SYMBOL(acpi_cpu_get_madt_gicc);
> > 
> > Why not EXPORT_SYMBOL_GPL()?
> 
> From what I understand, this could be made EXPORT_SYMBOL_GPL().
> The only reason was that the other symbol exportation in the
> file wasn't restricted to GPL.

I'm personally keen on keeping this for GPL code only, just like the
current code is. If there is a further need to relax this, we can
discuss it separately.

> 
> > 
> >> 
> >>   /*
> >>    * acpi_map_gic_cpu_interface - parse processor MADT entry
> >> diff --git a/drivers/cpufreq/cppc_cpufreq.c
> >> b/drivers/cpufreq/cppc_cpufreq.c
> >> index 8f950fe72765..a6cd95c3b474 100644
> >> --- a/drivers/cpufreq/cppc_cpufreq.c
> >> +++ b/drivers/cpufreq/cppc_cpufreq.c
> >> @@ -422,12 +422,66 @@ static unsigned int
> >> cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
> >>   	return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
> >>   }
> >> 
> >> +static bool efficiency_class_populated;
> >> +static DEFINE_PER_CPU(unsigned int, efficiency_class);
> >> +
> >> +static int populate_efficiency_class(void)
> >> +{
> >> +	unsigned int min = UINT_MAX, max = 0, class;
> >> +	struct acpi_madt_generic_interrupt *gicc;
> >> +	int cpu;
> >> +
> >> +	for_each_possible_cpu(cpu) {
> >> +		gicc = acpi_cpu_get_madt_gicc(cpu);
> >> +		if (!gicc)
> >> +			return -ENODEV;
> > 
> > How can that happen if you made it here using ACPI?
> 
> This is effectively an extra check. This could be removed.

Please do.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.