linux-kernel - Re: [PATCH v3 05/21] ACPI: CPPC: add cppc enable register function

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Date:   Mon, 1 Nov 2021 17:20:00 +0800
From:   Huang Rui <ray.huang@....com>
To:     "Limonciello, Mario" <Mario.Limonciello@....com>
Cc:     "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "Sharma, Deepak" <Deepak.Sharma@....com>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        Steven Noonan <steven@...vesoftware.com>,
        "Fontenot, Nathan" <Nathan.Fontenot@....com>,
        "Su, Jinzhou (Joe)" <Jinzhou.Su@....com>,
        "Du, Xiaojian" <Xiaojian.Du@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v3 05/21] ACPI: CPPC: add cppc enable register function

On Fri, Oct 29, 2021 at 10:15:35PM +0800, Limonciello, Mario wrote:
> On 10/29/2021 08:02, Huang Rui wrote:
> > From: Jinzhou Su <Jinzhou.Su@....com>
> > 
> > Add a new function to enable CPPC feature. This function
> > will write Continuous Performance Control package
> > EnableRegister field on the processor.
> > 
> > CPPC EnableRegister register described in section 8.4.7.1 of ACPI 6.4:
> > This element is optional. If supported, contains a resource descriptor
> > with a single Register() descriptor that describes a register to which
> > OSPM writes a One to enable CPPC on this processor. Before this register
> > is set, the processor will be controlled by legacy mechanisms (ACPI
> > Pstates, firmware, etc.).
> > 
> > This register will be used for AMD processors to enable amd-pstate
> > function instead of legacy ACPI P-States.
> > 
> > Signed-off-by: Jinzhou Su <Jinzhou.Su@....com>
> > Signed-off-by: Huang Rui <ray.huang@....com>
> > ---
> >   drivers/acpi/cppc_acpi.c | 45 ++++++++++++++++++++++++++++++++++++++++
> >   include/acpi/cppc_acpi.h |  5 +++++
> >   2 files changed, 50 insertions(+)
> > 
> > diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> > index c9169c221209..2d2297ef5bf9 100644
> > --- a/drivers/acpi/cppc_acpi.c
> > +++ b/drivers/acpi/cppc_acpi.c
> > @@ -1275,6 +1275,51 @@ int cppc_get_perf_ctrs(int cpunum, struct cppc_perf_fb_ctrs *perf_fb_ctrs)
> >   }
> >   EXPORT_SYMBOL_GPL(cppc_get_perf_ctrs);
> >   
> > +/**
> > + * cppc_set_enable - Set to enable CPPC on the processor by writing the
> > + * Continuous Performance Control package EnableRegister feild.
> 
> s/feild/field/
> 
> > + * @cpu: CPU for which to enable CPPC register.
> > + * @enable: 0 - disable, 1 - enable CPPC feature on the processor.
> > + *
> > + * Return: 0 for success, -ERRNO or -EIO otherwise.
> > + */
> > +int cppc_set_enable(int cpu, bool enable)
> > +{
> > +	int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
> > +	struct cpc_register_resource *enable_reg;
> > +	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
> > +	struct cppc_pcc_data *pcc_ss_data = NULL;
> > +	int ret = -EINVAL;
> > +
> > +	if (!cpc_desc) {
> > +		pr_debug("No CPC descriptor for CPU:%d\n", cpu);
> > +		return -EINVAL;
> > +	}
> 
> Can this actually happen or is just an extra safety check?
> Don't you block running based on acpi_cpc_valid?
> 

It's a helper function in cppc lib, is this possible called on other driver
might not be protected by acpi_cpc_valid in future?

Thanks,
Ray