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Message-ID: <b68a4273-ad39-4d3e-a556-1b409b50944d@arm.com>
Date: Thu, 22 Jan 2026 12:36:55 +0100
From: Pierre Gondois <pierre.gondois@....com>
To: Sumit Gupta <sumitg@...dia.com>, rafael@...nel.org,
viresh.kumar@...aro.org, zhenglifeng1@...wei.com, ionela.voinescu@....com,
lenb@...nel.org, robert.moore@...el.com, corbet@....net,
rdunlap@...radead.org, ray.huang@....com, gautham.shenoy@....com,
mario.limonciello@....com, perry.yuan@....com, zhanjie9@...ilicon.com,
linux-pm@...r.kernel.org, linux-acpi@...r.kernel.org,
linux-doc@...r.kernel.org, acpica-devel@...ts.linux.dev,
linux-kernel@...r.kernel.org
Cc: linux-tegra@...r.kernel.org, treding@...dia.com, jonathanh@...dia.com,
vsethi@...dia.com, ksitaraman@...dia.com, sanjayc@...dia.com,
nhartman@...dia.com, bbasu@...dia.com
Subject: Re: [PATCH v6 6/9] ACPI: CPPC: add APIs and sysfs interface for
min/max_perf
On 1/20/26 15:56, 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@...dia.com>
> ---
> 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);
> +}
> +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);
> +
Shouldn't concurrent access be handled by the policy->rwsem ?
I think this can be checked using either:
- lockdep_assert_held_write(&policy->rwsem)
- lockdep_assert_held_read(&policy->rwsem)
in store/show_max_perf() for instance.
> #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;
> +}
> +
> static struct cppc_cpudata *cppc_cpufreq_get_cpu_data(unsigned int cpu)
> {
> struct cppc_cpudata *cpu_data;
> @@ -918,16 +949,142 @@ CPPC_CPUFREQ_ATTR_RW_U64(auto_act_window, cppc_get_auto_act_window,
> CPPC_CPUFREQ_ATTR_RW_U64(energy_performance_preference_val,
> cppc_get_epp_perf, cppc_set_epp)
>
> +/**
> + * show_min_perf - Show minimum performance as frequency (kHz)
> + * @policy: cpufreq policy
> + * @buf: buffer to write the frequency value to
> + *
> + * Reads the MIN_PERF register and converts the performance value to
> + * frequency (kHz).
> + */
> +static ssize_t show_min_perf(struct cpufreq_policy *policy, char *buf)
> +{
> + struct cppc_cpudata *cpu_data = policy->driver_data;
> + struct cppc_perf_caps *caps = &cpu_data->perf_caps;
> + u64 perf;
> + int ret;
> +
> + ret = cppc_get_min_perf(policy->cpu, &perf);
> + if (ret == -EOPNOTSUPP)
> + return sysfs_emit(buf, "<unsupported>\n");
> + if (ret)
> + return ret;
> +
> + /* Use lowest_perf if register is uninitialized (0) */
> + if (perf == 0)
> + perf = caps->lowest_perf;
> +
> + /* Convert performance to frequency (kHz) for user */
> + return sysfs_emit(buf, "%u\n", cppc_perf_to_khz(caps, perf));
> +}
> +
> +/**
> + * store_min_perf - Set minimum performance from frequency (kHz)
> + * @policy: cpufreq policy
> + * @buf: buffer containing the frequency value
> + * @count: size of @buf
> + *
> + * Converts the user-provided frequency (kHz) to a performance value
> + * and writes it to the MIN_PERF register.
> + */
> +static ssize_t store_min_perf(struct cpufreq_policy *policy, const char *buf,
> + size_t count)
> +{
> + struct cppc_cpudata *cpu_data = policy->driver_data;
> + unsigned int freq_khz;
> + u64 perf;
> + int ret;
> +
> + ret = kstrtouint(buf, 0, &freq_khz);
> + if (ret)
> + return ret;
> +
> + /* Convert frequency (kHz) to performance value */
> + perf = cppc_khz_to_perf(&cpu_data->perf_caps, freq_khz);
> +
> + guard(mutex)(&cppc_cpufreq_autonomous_lock);
> + ret = cppc_cpufreq_set_mperf_reg(policy, perf, true);
> + if (ret)
> + return ret;
> +
> + return count;
> +}
> +
> +/**
> + * show_max_perf - Show maximum performance as frequency (kHz)
> + * @policy: cpufreq policy
> + * @buf: buffer to write the frequency value to
> + *
> + * Reads the MAX_PERF register and converts the performance value to
> + * frequency (kHz).
> + */
> +static ssize_t show_max_perf(struct cpufreq_policy *policy, char *buf)
> +{
> + struct cppc_cpudata *cpu_data = policy->driver_data;
> + struct cppc_perf_caps *caps = &cpu_data->perf_caps;
> + u64 perf;
> + int ret;
> +
> + ret = cppc_get_max_perf(policy->cpu, &perf);
> + if (ret == -EOPNOTSUPP)
> + return sysfs_emit(buf, "<unsupported>\n");
> + if (ret)
> + return ret;
> +
> + /* Use highest_perf if register is uninitialized or out of range */
> + if (perf == 0 || perf > caps->highest_perf)
> + perf = caps->highest_perf;
> +
> + /* Convert performance to frequency (kHz) for user */
> + return sysfs_emit(buf, "%u\n", cppc_perf_to_khz(caps, perf));
> +}
> +
> +/**
> + * store_max_perf - Set maximum performance from frequency (kHz)
> + * @policy: cpufreq policy
> + * @buf: buffer containing the frequency value
> + * @count: size of @buf
> + *
> + * Converts the user-provided frequency (kHz) to a performance value
> + * and writes it to the MAX_PERF register.
> + */
> +static ssize_t store_max_perf(struct cpufreq_policy *policy, const char *buf,
> + size_t count)
> +{
> + struct cppc_cpudata *cpu_data = policy->driver_data;
> + unsigned int freq_khz;
> + u64 perf;
> + int ret;
> +
> + ret = kstrtouint(buf, 0, &freq_khz);
> + if (ret)
> + return ret;
> +
> + /* Convert frequency (kHz) to performance value */
> + perf = cppc_khz_to_perf(&cpu_data->perf_caps, freq_khz);
> +
> + guard(mutex)(&cppc_cpufreq_autonomous_lock);
> + ret = cppc_cpufreq_set_mperf_reg(policy, perf, false);
> + if (ret)
> + return ret;
> +
> + return count;
> +}
> +
> cpufreq_freq_attr_ro(freqdomain_cpus);
> cpufreq_freq_attr_rw(auto_select);
> cpufreq_freq_attr_rw(auto_act_window);
> cpufreq_freq_attr_rw(energy_performance_preference_val);
> +cpufreq_freq_attr_rw(min_perf);
> +cpufreq_freq_attr_rw(max_perf);
>
> static struct freq_attr *cppc_cpufreq_attr[] = {
> &freqdomain_cpus,
> &auto_select,
> &auto_act_window,
> &energy_performance_preference_val,
> + &min_perf,
> + &max_perf,
> NULL,
> };
>
> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
> index 3fc796c0d902..b358440cd0e2 100644
> --- a/include/acpi/cppc_acpi.h
> +++ b/include/acpi/cppc_acpi.h
> @@ -174,6 +174,10 @@ extern int cppc_get_auto_act_window(int cpu, u64 *auto_act_window);
> extern int cppc_set_auto_act_window(int cpu, u64 auto_act_window);
> extern int cppc_get_auto_sel(int cpu, bool *enable);
> extern int cppc_set_auto_sel(int cpu, bool enable);
> +extern int cppc_get_min_perf(int cpu, u64 *min_perf);
> +extern int cppc_set_min_perf(int cpu, u32 min_perf);
> +extern int cppc_get_max_perf(int cpu, u64 *max_perf);
> +extern int cppc_set_max_perf(int cpu, u32 max_perf);
> extern int amd_get_highest_perf(unsigned int cpu, u32 *highest_perf);
> extern int amd_get_boost_ratio_numerator(unsigned int cpu, u64 *numerator);
> extern int amd_detect_prefcore(bool *detected);
> @@ -270,6 +274,22 @@ static inline int cppc_set_auto_sel(int cpu, bool enable)
> {
> return -EOPNOTSUPP;
> }
> +static inline int cppc_get_min_perf(int cpu, u64 *min_perf)
> +{
> + return -EOPNOTSUPP;
> +}
> +static inline int cppc_set_min_perf(int cpu, u32 min_perf)
> +{
> + return -EOPNOTSUPP;
> +}
> +static inline int cppc_get_max_perf(int cpu, u64 *max_perf)
> +{
> + return -EOPNOTSUPP;
> +}
> +static inline int cppc_set_max_perf(int cpu, u32 max_perf)
> +{
> + return -EOPNOTSUPP;
> +}
> static inline int amd_get_highest_perf(unsigned int cpu, u32 *highest_perf)
> {
> return -ENODEV;
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