Re: [PATCH v6 6/9] ACPI: CPPC: add APIs and sysfs interface for min/max_perf

[Sumit Gupta]

On 22/01/26 18:05, zhenglifeng (A) wrote:
> External email: Use caution opening links or attachments
>
>
> On 2026/1/20 22:56, Sumit Gupta wrote:
> > Add cppc_get/set_min_perf() and cppc_get/set_max_perf() APIs to read and
> > write the MIN_PERF and MAX_PERF registers.
> >
> > Also add sysfs interfaces (min_perf, max_perf) in cppc_cpufreq driver
> > to expose these controls to userspace. The sysfs values are in frequency
> > (kHz) for consistency with other cpufreq sysfs files.
> >
> > A mutex is used to serialize sysfs store operations to ensure hardware
> > register writes and perf_ctrls updates are atomic.
> >
> > Signed-off-by: Sumit Gupta <sumitg@xxxxxxxxxx>
> > ---
> >   drivers/acpi/cppc_acpi.c       |  44 +++++++++
> >   drivers/cpufreq/cppc_cpufreq.c | 157 +++++++++++++++++++++++++++++++++
> >   include/acpi/cppc_acpi.h       |  20 +++++
> >   3 files changed, 221 insertions(+)
> >
> > diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> > index 45c6bd6ec24b..46bf45f8b0f3 100644
> > --- a/drivers/acpi/cppc_acpi.c
> > +++ b/drivers/acpi/cppc_acpi.c
> > @@ -1743,6 +1743,50 @@ int cppc_set_auto_sel(int cpu, bool enable)
> >   }
> >   EXPORT_SYMBOL_GPL(cppc_set_auto_sel);
> >
> > +/**
> > + * cppc_get_min_perf - Read minimum performance register.
> > + * @cpu: CPU from which to read register.
> > + * @min_perf: Return address.
> > + */
> > +int cppc_get_min_perf(int cpu, u64 *min_perf)
> > +{
> > +     return cppc_get_reg_val(cpu, MIN_PERF, min_perf);
> > +}
> > +EXPORT_SYMBOL_GPL(cppc_get_min_perf);
> > +
> > +/**
> > + * cppc_set_min_perf - Write minimum performance register.
> > + * @cpu: CPU to which to write register.
> > + * @min_perf: the desired minimum performance value to be updated.
> > + */
> > +int cppc_set_min_perf(int cpu, u32 min_perf)
> > +{
> > +     return cppc_set_reg_val(cpu, MIN_PERF, min_perf);
> ACPI spec says it 'must be set to a value that is less than or equal to
> that specified by the Maximum Performance Register'. So it may be better
> to check it before setting value.

Yes, I added that check in v1[1]. But missed adding it in later versions.
Will add below check in v7. Thank you for pointing.
--------
  static ssize_t store_min_perf(struct cpufreq_policy *policy, const 
char *buf,
                              size_t count)
  {
        .....
        /* Convert frequency (kHz) to performance value */
        perf = cppc_khz_to_perf(&cpu_data->perf_caps, freq_khz);

+       if (perf > cpu_data->perf_ctrls.max_perf)
+               return -EINVAL;
--------
[1] https://lore.kernel.org/lkml/20250211103737.447704-4-sumitg@xxxxxxxxxx/

> > +}
> > +EXPORT_SYMBOL_GPL(cppc_set_min_perf);
> > +
> > +/**
> > + * cppc_get_max_perf - Read maximum performance register.
> > + * @cpu: CPU from which to read register.
> > + * @max_perf: Return address.
> > + */
> > +int cppc_get_max_perf(int cpu, u64 *max_perf)
> > +{
> > +     return cppc_get_reg_val(cpu, MAX_PERF, max_perf);
> > +}
> > +EXPORT_SYMBOL_GPL(cppc_get_max_perf);
> > +
> > +/**
> > + * cppc_set_max_perf - Write maximum performance register.
> > + * @cpu: CPU to which to write register.
> > + * @max_perf: the desired maximum performance value to be updated.
> > + */
> > +int cppc_set_max_perf(int cpu, u32 max_perf)
> > +{
> > +     return cppc_set_reg_val(cpu, MAX_PERF, max_perf);
> > +}
> > +EXPORT_SYMBOL_GPL(cppc_set_max_perf);
> > +
> >   /**
> >    * cppc_set_enable - Set to enable CPPC on the processor by writing the
> >    * Continuous Performance Control package EnableRegister field.
> > diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> > index 229880c4eedb..66e183b45fb0 100644
> > --- a/drivers/cpufreq/cppc_cpufreq.c
> > +++ b/drivers/cpufreq/cppc_cpufreq.c
> > @@ -28,6 +28,8 @@
> >
> >   static struct cpufreq_driver cppc_cpufreq_driver;
> >
> > +static DEFINE_MUTEX(cppc_cpufreq_autonomous_lock);
> > +
> >   #ifdef CONFIG_ACPI_CPPC_CPUFREQ_FIE
> >   static enum {
> >        FIE_UNSET = -1,
> > @@ -570,6 +572,35 @@ static void populate_efficiency_class(void)
> >   }
> >   #endif
> >
> > +/* Set min/max performance HW register and cache the value */
> > +static int cppc_cpufreq_set_mperf_reg(struct cpufreq_policy *policy,
> > +                                   u64 val, bool is_min)
> > +{
> > +     struct cppc_cpudata *cpu_data = policy->driver_data;
> > +     struct cppc_perf_caps *caps = &cpu_data->perf_caps;
> > +     unsigned int cpu = policy->cpu;
> > +     u32 perf;
> > +     int ret;
> > +
> > +     perf = clamp(val, caps->lowest_perf, caps->highest_perf);
> > +
> > +     ret = is_min ? cppc_set_min_perf(cpu, perf) :
> > +                    cppc_set_max_perf(cpu, perf);
> > +     if (ret) {
> > +             if (ret != -EOPNOTSUPP)
> > +                     pr_warn("CPU%d: set %s_perf=%u failed (%d)\n",
> > +                             cpu, is_min ? "min" : "max", perf, ret);
> > +             return ret;
> > +     }
> > +
> > +     if (is_min)
> > +             cpu_data->perf_ctrls.min_perf = perf;
> > +     else
> > +             cpu_data->perf_ctrls.max_perf = perf;
> > +
> > +     return 0;
> I think cppc_set_XXX and updating cpudata->perf_ctrls.XXX can be extract
> out for not only min_perf and max_perf but also auto_sel and energy_perf
> and anything else in perf_ctrls.

Updating cached value of auto_sel and energy_perf in patch 9.
I think the current code is simple. Adding an abstraction seems to be
overdoing it for this case.

Thank you,
Sumit Gupta

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