Re: [PATCH v2] cpufreq: CPPC: Set CPPC Enable register in cpu_init

[Rafael J. Wysocki (Intel)]

On Tue, Nov 10, 2026 at 11:58 AM Christian Loehle
<christian.loehle@xxxxxxx> wrote:
>
> On 11/10/26 10:12, Sumit Gupta wrote:
> > As per ACPI 6.x s8.4.6.1.4 (CPPC Enable Register):
> >   "If supported by the platform, OSPM writes a one to this register
> >    to enable CPPC on this processor. If not implemented, OSPM assumes
> >    the platform always has CPPC enabled."
> >
> > The driver never writes this register. CPPC therefore stays disabled
> > on platforms such as NVIDIA GB10 that wait for OSPM to enable it.
> >
> > Call cppc_set_enable() in cppc_cpufreq_cpu_init(). Fail init if
> > enabling CPPC fails. If init fails after CPPC is enabled, disable it
> > again. The register is optional, so -EOPNOTSUPP is not an error.
> >
> > This relies on commit ab482f1bac6b ("ACPI: CPPC: Refactor register
> > value get and set ABIs") from v6.16. Before it, cppc_set_enable()
> > returned -EFAULT instead of -EOPNOTSUPP when the Enable register is
> > not implemented. On an older kernel this change would make init fail
> > on every platform without the register, so the stable range starts
> > at v6.16.
> >
> > Fixes: 5477fb3bd1e8 ("ACPI / CPPC: Add a CPUFreq driver for use with CPPC")
> > Cc: stable@xxxxxxxxxxxxxxx # v6.16+
> > Signed-off-by: Sumit Gupta <sumitg@xxxxxxxxxx>
>
> Reviewed-by: Christian Loehle <christian.loehle@xxxxxxx>

Applied as 7.4-rc material, thanks!

> > ---
> > v1 -> v2:
> > - Fail init if enabling CPPC fails and disable CPPC again if init
> >   fails after enabling it (Christian).
> > - Move enable after the policy->shared_type check, so cppc_set_perf()
> >   is the only failure after it.
> > - Mention NVIDIA GB10 in the commit message (Christian).
> >
> > v1: https://lore.kernel.org/lkml/20261105123244.3132560-1-sumitg@xxxxxxxxxx/
> >
> >  drivers/cpufreq/cppc_cpufreq.c | 14 +++++++++++++-
> >  1 file changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> > index 957fa7775260..b2af24ae5008 100644
> > --- a/drivers/cpufreq/cppc_cpufreq.c
> > +++ b/drivers/cpufreq/cppc_cpufreq.c
> > @@ -714,7 +714,17 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
> >               pr_debug("Unsupported CPU co-ord type: %d\n",
> >                        policy->shared_type);
> >               ret = -EFAULT;
> > -             goto out;
> > +             goto out_put;
> > +     }
> > +
> > +     /*
> > +      * Enable CPPC. The Enable register is optional - some platforms
> > +      * may not support it.
> > +      */
> > +     ret = cppc_set_enable(cpu, true);
> > +     if (ret && ret != -EOPNOTSUPP) {
> > +             pr_err("Failed to enable CPPC for CPU%u (%d)\n", cpu, ret);
> > +             goto out_put;
> >       }
> >
> >       policy->fast_switch_possible = cppc_allow_fast_switch(policy->cpus);
> > @@ -742,6 +752,8 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
> >       return 0;
> >
> >  out:
> > +     cppc_set_enable(cpu, false);
> > +out_put:
> >       cppc_cpufreq_put_cpu_data(policy);
> >       return ret;
> >  }
>