[PATCH v6 0/2] ACPI / cpufreq: CPPC: Add ospm_nominal_perf support

[PATCH v6 0/2] ACPI / cpufreq: CPPC: Add ospm_nominal_perf support

[Sumit Gupta]

This series adds support for the OSPM Nominal Performance register
(ACPI 6.6, Section 8.4.6.1.2.6) to the CPPC ACPI and cpufreq drivers.

Unlike the read-only Nominal Performance register, OSPM Nominal
Performance is writable and lets OSPM request a nominal level below
the platform-reported nominal. The platform treats performance above
this level as boost and below as throttle for its power and thermal
decisions.

Patch 1: adds the cppc_{get,set}_ospm_nominal_perf() helpers, a
per-policy cpufreq sysfs attribute (ospm_nominal_freq, in kHz), and
hooks the register into the OSPM-set save/restore table.

Patch 2: reflects the OSPM nominal in the cpufreq policy so that boost
and the frequency limits stay consistent with the register.

This series applies on top of the series
"cpufreq: CPPC: Preserve OSPM-set registers across hotplug and unload",
which provides the save/restore table that patch 1 hooks into:
https://lore.kernel.org/lkml/20260716153820.2007095-1-sumitg@nvidia.com/

v5[5] -> v6:
- New patch 2: reflect the OSPM nominal in the policy's boost state
  and frequency limits.
- Patch 1:
  - write only policy->cpu instead of looping over policy->cpus with
    rollback. the register is treated as shared across a policy's CPUs.
  - add the register to the OSPM-set save/restore table.

Sumit Gupta (2):
  ACPI: CPPC: Add ospm_nominal_perf support
  cpufreq: CPPC: Reflect ospm_nominal_perf in boost and limits

 .../ABI/testing/sysfs-devices-system-cpu      |  26 +++
 drivers/acpi/cppc_acpi.c                      |  32 ++++
 drivers/cpufreq/cppc_cpufreq.c                | 166 +++++++++++++++++-
 include/acpi/cppc_acpi.h                      |  10 ++
 4 files changed, 226 insertions(+), 8 deletions(-)

v5: https://lore.kernel.org/lkml/20260615185934.2383514-1-sumitg@nvidia.com/
v4: https://lore.kernel.org/lkml/20260527194626.185286-1-sumitg@nvidia.com/
v3: https://lore.kernel.org/lkml/20260514194822.1841748-1-sumitg@nvidia.com/
v2: https://lore.kernel.org/lkml/20260430142430.755437-1-sumitg@nvidia.com/
v1: https://lore.kernel.org/lkml/20260427051823.280419-1-sumitg@nvidia.com/

-- 
2.34.1

[PATCH v6 1/2] ACPI: CPPC: Add ospm_nominal_perf support

[Sumit Gupta]

Expose the OSPM Nominal Performance register (ACPI 6.6, Section
8.4.6.1.2.6), which conveys the desired nominal performance level
at which the platform may run. Unlike the existing read-only
Nominal Performance register, it is writable and lets OSPM
request a lower nominal level than the platform-reported nominal.
The platform classifies performance above this level as boosted
and below as throttled for its power/thermal decisions.

It is exposed as a per-policy cpufreq sysfs attribute in kHz, to
match the cpufreq sysfs unit convention:

  /sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq

The attribute is documented in
Documentation/ABI/testing/sysfs-devices-system-cpu.

Writes are converted to perf via cppc_khz_to_perf(), validated
against [Lowest Performance, Nominal Performance], and applied to
the policy->cpu. The register is assumed shared across the
policy->cpus.

On read, the current register value is returned, or
"<unsupported>" if the platform does not implement the register.

Also add the register to the OSPM-set register save/restore
table, so its value survives CPU hotplug and reverts to the
firmware value on driver unload, like the other registers in
the table.

Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
---
 .../ABI/testing/sysfs-devices-system-cpu      | 26 ++++++++++
 drivers/acpi/cppc_acpi.c                      | 32 +++++++++++++
 drivers/cpufreq/cppc_cpufreq.c                | 47 +++++++++++++++++++
 include/acpi/cppc_acpi.h                      | 10 ++++
 4 files changed, 115 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 82d10d556cc8..a8d592c08823 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -346,6 +346,32 @@ Description:	Performance Limited
 
 		This file is only present if the cppc-cpufreq driver is in use.
 
+What:		/sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq
+Date:		May 2026
+Contact:	linux-pm@vger.kernel.org
+Description:	OSPM Nominal Performance (kHz)
+
+		OSPM uses this attribute to request a nominal performance
+		level lower than the platform-reported nominal. The
+		platform treats performance above this level as boost
+		and below as throttle for power and thermal decisions.
+
+		Read returns the current value in kHz, or "<unsupported>"
+		if the platform does not implement the register. Write a
+		kHz value in the range [lowest_freq, nominal_freq].
+
+		Note that tasks may be migrated from one CPU to another
+		by the scheduler's load-balancing algorithm, and if
+		different OSPM Nominal Performance values are set for
+		those CPUs (through different cpufreq policies), that may
+		lead to undesirable outcomes. To avoid such issues it is
+		better to set the same value across all policies, or to
+		pin every task potentially sensitive to it to a specific
+		CPU.
+
+		This file is only present if the cppc-cpufreq driver is
+		in use.
+
 What:		/sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
 Date:		August 2008
 KernelVersion:	2.6.27
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index a7fec6c93178..681d4fd40c11 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1685,6 +1685,38 @@ int cppc_set_epp(int cpu, u64 epp_val)
 }
 EXPORT_SYMBOL_GPL(cppc_set_epp);
 
+/**
+ * cppc_set_ospm_nominal_perf() - Write OSPM Nominal Performance register.
+ * @cpu: CPU on which to write register.
+ * @ospm_nominal_perf: Value to write to the OSPM Nominal Performance register.
+ *
+ * OSPM Nominal Performance conveys the desired nominal performance level
+ * at which the platform may run. Per ACPI 6.6, s8.4.6.1.2.6, the value
+ * must lie within [Lowest Performance, Nominal Performance] and may be
+ * set independently of Minimum, Maximum and Desired performance. The
+ * caller is responsible for validating the range.
+ *
+ * Return: 0 on success or negative error code.
+ */
+int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
+{
+	return cppc_set_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
+}
+EXPORT_SYMBOL_GPL(cppc_set_ospm_nominal_perf);
+
+/**
+ * cppc_get_ospm_nominal_perf() - Read OSPM Nominal Performance register.
+ * @cpu: CPU from which to read register.
+ * @ospm_nominal_perf: Pointer to store the OSPM Nominal Performance value.
+ *
+ * Return: 0 on success or negative error code.
+ */
+int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf)
+{
+	return cppc_get_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
+}
+EXPORT_SYMBOL_GPL(cppc_get_ospm_nominal_perf);
+
 /**
  * cppc_get_auto_act_window() - Read autonomous activity window register.
  * @cpu: CPU from which to read register.
diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 9c88512d635c..eb6746810fa6 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -37,6 +37,7 @@ enum cppc_saved_reg_id {
 	CPPC_SAVED_AUTO_SEL,
 	CPPC_SAVED_EPP,
 	CPPC_SAVED_AUTO_ACT_WINDOW,
+	CPPC_SAVED_OSPM_NOMINAL_PERF,
 	CPPC_NR_SAVED_REGS,
 };
 
@@ -55,6 +56,9 @@ static const struct cppc_saved_reg cppc_saved_regs[CPPC_NR_SAVED_REGS] = {
 	[CPPC_SAVED_AUTO_ACT_WINDOW] = {
 		cppc_get_auto_act_window, cppc_set_auto_act_window,
 	},
+	[CPPC_SAVED_OSPM_NOMINAL_PERF] = {
+		cppc_get_ospm_nominal_perf, cppc_set_ospm_nominal_perf,
+	},
 };
 
 /*
@@ -1166,11 +1170,53 @@ static int cppc_get_perf_limited_filtered(int cpu, u64 *perf_limited)
 CPPC_CPUFREQ_ATTR_RW_U64(perf_limited, cppc_get_perf_limited_filtered,
 			 cppc_set_perf_limited)
 
+static ssize_t show_ospm_nominal_freq(struct cpufreq_policy *policy, char *buf)
+{
+	struct cppc_cpudata *cpu_data = policy->driver_data;
+	u64 perf;
+	int ret;
+
+	ret = cppc_get_ospm_nominal_perf(policy->cpu, &perf);
+	if (ret == -EOPNOTSUPP)
+		return sysfs_emit(buf, "<unsupported>\n");
+	if (ret)
+		return ret;
+
+	return sysfs_emit(buf, "%u\n",
+			  cppc_perf_to_khz(&cpu_data->perf_caps, perf));
+}
+
+static ssize_t store_ospm_nominal_freq(struct cpufreq_policy *policy,
+				       const char *buf, size_t count)
+{
+	struct cppc_cpudata *cpu_data = policy->driver_data;
+	unsigned int freq_khz;
+	u32 perf;
+	int ret;
+
+	ret = kstrtouint(buf, 0, &freq_khz);
+	if (ret)
+		return ret;
+
+	perf = cppc_khz_to_perf(&cpu_data->perf_caps, freq_khz);
+	if (perf < cpu_data->perf_caps.lowest_perf ||
+	    perf > cpu_data->perf_caps.nominal_perf)
+		return -EINVAL;
+
+	/* The register is assumed shared across the policy's CPUs. */
+	ret = cppc_set_ospm_nominal_perf(policy->cpu, perf);
+	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(perf_limited);
+cpufreq_freq_attr_rw(ospm_nominal_freq);
 
 static struct freq_attr *cppc_cpufreq_attr[] = {
 	&freqdomain_cpus,
@@ -1178,6 +1224,7 @@ static struct freq_attr *cppc_cpufreq_attr[] = {
 	&auto_act_window,
 	&energy_performance_preference_val,
 	&perf_limited,
+	&ospm_nominal_freq,
 	NULL,
 };
 
diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index cd07e1e92bf4..4c9e59643cc0 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -180,6 +180,8 @@ extern int cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val);
 extern int cppc_get_epp_perf(int cpunum, u64 *epp_perf);
 extern int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable);
 extern int cppc_set_epp(int cpu, u64 epp_val);
+extern int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf);
+extern int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf);
 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);
@@ -268,6 +270,14 @@ static inline int cppc_set_epp(int cpu, u64 epp_val)
 {
 	return -EOPNOTSUPP;
 }
+static inline int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
+{
+	return -EOPNOTSUPP;
+}
+static inline int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf)
+{
+	return -EOPNOTSUPP;
+}
 static inline int cppc_get_auto_act_window(int cpu, u64 *auto_act_window)
 {
 	return -EOPNOTSUPP;
-- 
2.34.1

[PATCH v6 2/2] cpufreq: CPPC: Reflect ospm_nominal_perf in boost and limits

[Sumit Gupta]

OSPM Nominal Performance lets OSPM request a nominal level below the
platform-reported nominal. Since boost is the range above nominal,
lowering the nominal enlarges the boost range and drops the non-boost
ceiling.

cppc_cpufreq currently uses the platform nominal as the non-boost
ceiling. Changing the OSPM nominal then leaves the policy limits
unchanged, so the boost and non-boost ranges no longer match the
register.

Reflect the OSPM nominal in the cpufreq policy so that boost and the
frequency limits stay consistent with the register:

  - Add cppc_cpufreq_get_effective_nominal(), which yields the OSPM
    Nominal Performance when set and the platform nominal otherwise.
  - Use it to derive cpuinfo.max_freq for the non-boost ceiling in init()
    and in set_boost() while boost is disabled.

The cpufreq core includes a per-policy boost QoS request among the
constraints that cap scaling_max_freq. It updates that request to match
cpuinfo.max_freq, but only when boost is toggled. Writing
ospm_nominal_freq changes cpuinfo.max_freq without toggling boost, so the
request (boost_freq_req) is left stale and keeps scaling_max_freq at the
old nominal. cppc_cpufreq_reflect_nominal() therefore updates the request
directly when the nominal changes while boost is disabled.

At boot, when highest_perf == nominal_perf there is no boost range, but
lowering the OSPM nominal later from sysfs can create one if
highest_perf > lowest_perf. Since the core registers its boost
FREQ_QOS_MAX request at policy setup only when boost_supported is already
set, set boost_supported in init() when the OSPM register is supported
and such a range is possible. Boost can then be enabled once the nominal
is lowered.

Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
---
 drivers/cpufreq/cppc_cpufreq.c | 119 ++++++++++++++++++++++++++++++---
 1 file changed, 111 insertions(+), 8 deletions(-)

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index eb6746810fa6..048bb567ec45 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -761,11 +761,63 @@ static void cppc_cpufreq_put_cpu_data(struct cpufreq_policy *policy)
 	policy->driver_data = NULL;
 }
 
+/**
+ * cppc_cpufreq_get_effective_nominal() - Get the effective nominal performance
+ * @policy: cpufreq policy associated with the CPU
+ * @nominal: Updated with the effective nominal performance
+ * @supported: Updated with whether OSPM Nominal Performance is supported.
+ *	       Pass NULL if not needed
+ *
+ * Use the OSPM Nominal Performance value when the register is supported and
+ * contains a nonzero value. Otherwise, use the platform-reported Nominal
+ * Performance. The resulting value is the non-boost performance ceiling.
+ *
+ * Return: 0 on success, or a negative error code if the register cannot be
+ * read or contains a value outside the supported performance range.
+ */
+static int cppc_cpufreq_get_effective_nominal(struct cpufreq_policy *policy,
+					      u32 *nominal, bool *supported)
+{
+	struct cppc_cpudata *cpu_data = policy->driver_data;
+	struct cppc_perf_caps *caps = &cpu_data->perf_caps;
+	u32 effective_nominal = caps->nominal_perf;
+	bool ospm_supported = false;
+	u64 ospm_nominal;
+	int ret;
+
+	ret = cppc_get_ospm_nominal_perf(policy->cpu, &ospm_nominal);
+	if (ret == -EOPNOTSUPP)
+		goto out;
+	if (ret)
+		return ret;
+
+	ospm_supported = true;
+
+	/* A zero value means OSPM has not selected a nominal level. */
+	if (!ospm_nominal)
+		goto out;
+
+	if (ospm_nominal < caps->lowest_perf ||
+	    ospm_nominal > caps->nominal_perf)
+		return -EINVAL;
+
+	effective_nominal = (u32)ospm_nominal;
+
+out:
+	*nominal = effective_nominal;
+	if (supported)
+		*supported = ospm_supported;
+
+	return 0;
+}
+
 static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
 {
 	unsigned int cpu = policy->cpu;
 	struct cppc_cpudata *cpu_data;
 	struct cppc_perf_caps *caps;
+	bool ospm_supported;
+	u32 nominal, perf;
 	int ret;
 
 	cpu_data = cppc_cpufreq_get_cpu_data(cpu);
@@ -788,8 +840,17 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
 	 * nonlinear perf
 	 */
 	policy->cpuinfo.min_freq = cppc_perf_to_khz(caps, caps->lowest_perf);
-	policy->cpuinfo.max_freq = cppc_perf_to_khz(caps, policy->boost_enabled ?
-						    caps->highest_perf : caps->nominal_perf);
+
+	ret = cppc_cpufreq_get_effective_nominal(policy, &nominal,
+						 &ospm_supported);
+	if (ret) {
+		pr_debug("CPU%u: failed to get effective nominal: %d\n",
+			 cpu, ret);
+		goto out;
+	}
+
+	perf = policy->boost_enabled ? caps->highest_perf : nominal;
+	policy->cpuinfo.max_freq = cppc_perf_to_khz(caps, perf);
 
 	policy->transition_delay_us = cppc_cpufreq_get_transition_delay_us(cpu);
 	policy->shared_type = cpu_data->shared_type;
@@ -819,9 +880,13 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
 
 	/*
 	 * If 'highest_perf' is greater than 'nominal_perf', we assume CPU Boost
-	 * is supported.
+	 * is supported. A writable OSPM Nominal Performance register can also
+	 * open a boost range at runtime by lowering the nominal, so assume
+	 * boost is supported in that case too, letting the core register its
+	 * QoS request up front.
 	 */
-	if (caps->highest_perf > caps->nominal_perf)
+	if (caps->highest_perf > caps->nominal_perf ||
+	    (ospm_supported && caps->highest_perf > caps->lowest_perf))
 		policy->boost_supported = true;
 
 	/* Set policy->cur to max now. The governors will adjust later. */
@@ -992,11 +1057,16 @@ static int cppc_cpufreq_set_boost(struct cpufreq_policy *policy, int state)
 {
 	struct cppc_cpudata *cpu_data = policy->driver_data;
 	struct cppc_perf_caps *caps = &cpu_data->perf_caps;
+	u32 perf = caps->highest_perf;
+	int ret;
 
-	if (state)
-		policy->cpuinfo.max_freq = cppc_perf_to_khz(caps, caps->highest_perf);
-	else
-		policy->cpuinfo.max_freq = cppc_perf_to_khz(caps, caps->nominal_perf);
+	if (!state) {
+		ret = cppc_cpufreq_get_effective_nominal(policy, &perf, NULL);
+		if (ret)
+			return ret;
+	}
+
+	policy->cpuinfo.max_freq = cppc_perf_to_khz(caps, perf);
 
 	return 0;
 }
@@ -1025,6 +1095,35 @@ static ssize_t show_auto_select(struct cpufreq_policy *policy, char *buf)
 	return sysfs_emit(buf, "%d\n", val);
 }
 
+static int cppc_cpufreq_reflect_nominal(struct cpufreq_policy *policy,
+					u32 nominal)
+{
+	struct cppc_cpudata *cpu_data = policy->driver_data;
+	int ret;
+
+	/*
+	 * While boost is disabled, the nominal is the ceiling. Set
+	 * cpuinfo.max_freq to it and update the core's boost_freq_req to
+	 * match. The core only syncs boost_freq_req when boost is enabled or
+	 * disabled, so a plain nominal change must update it here.
+	 */
+	if (!policy->boost_enabled) {
+		policy->cpuinfo.max_freq =
+			cppc_perf_to_khz(&cpu_data->perf_caps, nominal);
+
+		if (freq_qos_request_active(&policy->boost_freq_req)) {
+			ret = freq_qos_update_request(&policy->boost_freq_req,
+						      policy->cpuinfo.max_freq);
+			if (ret < 0)
+				return ret;
+		}
+	}
+
+	refresh_frequency_limits(policy);
+
+	return 0;
+}
+
 static ssize_t store_auto_select(struct cpufreq_policy *policy,
 				 const char *buf, size_t count)
 {
@@ -1208,6 +1307,10 @@ static ssize_t store_ospm_nominal_freq(struct cpufreq_policy *policy,
 	if (ret)
 		return ret;
 
+	ret = cppc_cpufreq_reflect_nominal(policy, perf);
+	if (ret)
+		return ret;
+
 	return count;
 }
 
-- 
2.34.1

Re: [PATCH v6 0/2] ACPI / cpufreq: CPPC: Add ospm_nominal_perf support

[Rafael J. Wysocki (Intel)]

On Fri, Jul 17, 2026 at 11:54 PM Sumit Gupta <sumitg@nvidia.com> wrote:
>
> This series adds support for the OSPM Nominal Performance register
> (ACPI 6.6, Section 8.4.6.1.2.6) to the CPPC ACPI and cpufreq drivers.
>
> Unlike the read-only Nominal Performance register, OSPM Nominal
> Performance is writable and lets OSPM request a nominal level below
> the platform-reported nominal. The platform treats performance above
> this level as boost and below as throttle for its power and thermal
> decisions.
>
> Patch 1: adds the cppc_{get,set}_ospm_nominal_perf() helpers, a
> per-policy cpufreq sysfs attribute (ospm_nominal_freq, in kHz), and
> hooks the register into the OSPM-set save/restore table.
>
> Patch 2: reflects the OSPM nominal in the cpufreq policy so that boost
> and the frequency limits stay consistent with the register.
>
> This series applies on top of the series
> "cpufreq: CPPC: Preserve OSPM-set registers across hotplug and unload",
> which provides the save/restore table that patch 1 hooks into:
> https://lore.kernel.org/lkml/20260716153820.2007095-1-sumitg@nvidia.com/
>
> v5[5] -> v6:
> - New patch 2: reflect the OSPM nominal in the policy's boost state
>   and frequency limits.
> - Patch 1:
>   - write only policy->cpu instead of looping over policy->cpus with
>     rollback. the register is treated as shared across a policy's CPUs.
>   - add the register to the OSPM-set save/restore table.

Christian, Pierre, any chance to have a look at this, please?

> Sumit Gupta (2):
>   ACPI: CPPC: Add ospm_nominal_perf support
>   cpufreq: CPPC: Reflect ospm_nominal_perf in boost and limits
>
>  .../ABI/testing/sysfs-devices-system-cpu      |  26 +++
>  drivers/acpi/cppc_acpi.c                      |  32 ++++
>  drivers/cpufreq/cppc_cpufreq.c                | 166 +++++++++++++++++-
>  include/acpi/cppc_acpi.h                      |  10 ++
>  4 files changed, 226 insertions(+), 8 deletions(-)
>
> v5: https://lore.kernel.org/lkml/20260615185934.2383514-1-sumitg@nvidia.com/
> v4: https://lore.kernel.org/lkml/20260527194626.185286-1-sumitg@nvidia.com/
> v3: https://lore.kernel.org/lkml/20260514194822.1841748-1-sumitg@nvidia.com/
> v2: https://lore.kernel.org/lkml/20260430142430.755437-1-sumitg@nvidia.com/
> v1: https://lore.kernel.org/lkml/20260427051823.280419-1-sumitg@nvidia.com/

Re: [PATCH v6 1/2] ACPI: CPPC: Add ospm_nominal_perf support

[Christian Loehle]

On 7/17/26 22:53, Sumit Gupta wrote:
> Expose the OSPM Nominal Performance register (ACPI 6.6, Section
> 8.4.6.1.2.6), which conveys the desired nominal performance level
> at which the platform may run. Unlike the existing read-only
> Nominal Performance register, it is writable and lets OSPM
> request a lower nominal level than the platform-reported nominal.
> The platform classifies performance above this level as boosted
> and below as throttled for its power/thermal decisions.
> 
> It is exposed as a per-policy cpufreq sysfs attribute in kHz, to
> match the cpufreq sysfs unit convention:
> 
>   /sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq
> 
> The attribute is documented in
> Documentation/ABI/testing/sysfs-devices-system-cpu.
> 
> Writes are converted to perf via cppc_khz_to_perf(), validated
> against [Lowest Performance, Nominal Performance], and applied to
> the policy->cpu. The register is assumed shared across the
> policy->cpus.
> 
> On read, the current register value is returned, or
> "<unsupported>" if the platform does not implement the register.
> 
> Also add the register to the OSPM-set register save/restore
> table, so its value survives CPU hotplug and reverts to the
> firmware value on driver unload, like the other registers in
> the table.
> 
> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
> ---
>  .../ABI/testing/sysfs-devices-system-cpu      | 26 ++++++++++
>  drivers/acpi/cppc_acpi.c                      | 32 +++++++++++++
>  drivers/cpufreq/cppc_cpufreq.c                | 47 +++++++++++++++++++
>  include/acpi/cppc_acpi.h                      | 10 ++++
>  4 files changed, 115 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> index 82d10d556cc8..a8d592c08823 100644
> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> @@ -346,6 +346,32 @@ Description:	Performance Limited
>  
>  		This file is only present if the cppc-cpufreq driver is in use.
>  
> +What:		/sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq
> +Date:		May 2026
> +Contact:	linux-pm@vger.kernel.org
> +Description:	OSPM Nominal Performance (kHz)
> +
> +		OSPM uses this attribute to request a nominal performance
> +		level lower than the platform-reported nominal. The
> +		platform treats performance above this level as boost
> +		and below as throttle for power and thermal decisions.
> +
> +		Read returns the current value in kHz, or "<unsupported>"
> +		if the platform does not implement the register. Write a
> +		kHz value in the range [lowest_freq, nominal_freq].
> +
> +		Note that tasks may be migrated from one CPU to another
> +		by the scheduler's load-balancing algorithm, and if
> +		different OSPM Nominal Performance values are set for
> +		those CPUs (through different cpufreq policies), that may
> +		lead to undesirable outcomes. To avoid such issues it is
> +		better to set the same value across all policies, or to
> +		pin every task potentially sensitive to it to a specific
> +		CPU.
> +
> +		This file is only present if the cppc-cpufreq driver is
> +		in use.
> +
>  What:		/sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
>  Date:		August 2008
>  KernelVersion:	2.6.27
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index a7fec6c93178..681d4fd40c11 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -1685,6 +1685,38 @@ int cppc_set_epp(int cpu, u64 epp_val)
>  }
>  EXPORT_SYMBOL_GPL(cppc_set_epp);
>  
> +/**
> + * cppc_set_ospm_nominal_perf() - Write OSPM Nominal Performance register.
> + * @cpu: CPU on which to write register.
> + * @ospm_nominal_perf: Value to write to the OSPM Nominal Performance register.
> + *
> + * OSPM Nominal Performance conveys the desired nominal performance level
> + * at which the platform may run. Per ACPI 6.6, s8.4.6.1.2.6, the value
> + * must lie within [Lowest Performance, Nominal Performance] and may be
> + * set independently of Minimum, Maximum and Desired performance. The
> + * caller is responsible for validating the range.
> + *
> + * Return: 0 on success or negative error code.
> + */
> +int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
> +{
> +	return cppc_set_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
> +}
> +EXPORT_SYMBOL_GPL(cppc_set_ospm_nominal_perf);
> +
> +/**
> + * cppc_get_ospm_nominal_perf() - Read OSPM Nominal Performance register.
> + * @cpu: CPU from which to read register.
> + * @ospm_nominal_perf: Pointer to store the OSPM Nominal Performance value.
> + *
> + * Return: 0 on success or negative error code.
> + */
> +int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf)
> +{
> +	return cppc_get_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
> +}
> +EXPORT_SYMBOL_GPL(cppc_get_ospm_nominal_perf);

It's a write-only register, we need to track everything in the driver.

> +
>  /**
>   * cppc_get_auto_act_window() - Read autonomous activity window register.
>   * @cpu: CPU from which to read register.
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index 9c88512d635c..eb6746810fa6 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -37,6 +37,7 @@ enum cppc_saved_reg_id {
>  	CPPC_SAVED_AUTO_SEL,
>  	CPPC_SAVED_EPP,
>  	CPPC_SAVED_AUTO_ACT_WINDOW,
> +	CPPC_SAVED_OSPM_NOMINAL_PERF,
>  	CPPC_NR_SAVED_REGS,
>  };
>  
> @@ -55,6 +56,9 @@ static const struct cppc_saved_reg cppc_saved_regs[CPPC_NR_SAVED_REGS] = {
>  	[CPPC_SAVED_AUTO_ACT_WINDOW] = {
>  		cppc_get_auto_act_window, cppc_set_auto_act_window,
>  	},
> +	[CPPC_SAVED_OSPM_NOMINAL_PERF] = {
> +		cppc_get_ospm_nominal_perf, cppc_set_ospm_nominal_perf,
> +	},
>  };
>  
>  /*
> @@ -1166,11 +1170,53 @@ static int cppc_get_perf_limited_filtered(int cpu, u64 *perf_limited)
>  CPPC_CPUFREQ_ATTR_RW_U64(perf_limited, cppc_get_perf_limited_filtered,
>  			 cppc_set_perf_limited)
>  
> +static ssize_t show_ospm_nominal_freq(struct cpufreq_policy *policy, char *buf)
> +{
> +	struct cppc_cpudata *cpu_data = policy->driver_data;
> +	u64 perf;
> +	int ret;
> +
> +	ret = cppc_get_ospm_nominal_perf(policy->cpu, &perf);
> +	if (ret == -EOPNOTSUPP)
> +		return sysfs_emit(buf, "<unsupported>\n");
> +	if (ret)
> +		return ret;
> +
> +	return sysfs_emit(buf, "%u\n",
> +			  cppc_perf_to_khz(&cpu_data->perf_caps, perf));
> +}
> +
> +static ssize_t store_ospm_nominal_freq(struct cpufreq_policy *policy,
> +				       const char *buf, size_t count)
> +{
> +	struct cppc_cpudata *cpu_data = policy->driver_data;
> +	unsigned int freq_khz;
> +	u32 perf;
> +	int ret;
> +
> +	ret = kstrtouint(buf, 0, &freq_khz);
> +	if (ret)
> +		return ret;
> +
> +	perf = cppc_khz_to_perf(&cpu_data->perf_caps, freq_khz);
> +	if (perf < cpu_data->perf_caps.lowest_perf ||
> +	    perf > cpu_data->perf_caps.nominal_perf)
> +		return -EINVAL;
> +
> +	/* The register is assumed shared across the policy's CPUs. */
> +	ret = cppc_set_ospm_nominal_perf(policy->cpu, perf);
> +	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(perf_limited);
> +cpufreq_freq_attr_rw(ospm_nominal_freq);
>  
>  static struct freq_attr *cppc_cpufreq_attr[] = {
>  	&freqdomain_cpus,
> @@ -1178,6 +1224,7 @@ static struct freq_attr *cppc_cpufreq_attr[] = {
>  	&auto_act_window,
>  	&energy_performance_preference_val,
>  	&perf_limited,
> +	&ospm_nominal_freq,
>  	NULL,
>  };
>  
> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
> index cd07e1e92bf4..4c9e59643cc0 100644
> --- a/include/acpi/cppc_acpi.h
> +++ b/include/acpi/cppc_acpi.h
> @@ -180,6 +180,8 @@ extern int cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val);
>  extern int cppc_get_epp_perf(int cpunum, u64 *epp_perf);
>  extern int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable);
>  extern int cppc_set_epp(int cpu, u64 epp_val);
> +extern int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf);
> +extern int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf);
>  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);
> @@ -268,6 +270,14 @@ static inline int cppc_set_epp(int cpu, u64 epp_val)
>  {
>  	return -EOPNOTSUPP;
>  }
> +static inline int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
> +{
> +	return -EOPNOTSUPP;
> +}
> +static inline int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf)
> +{
> +	return -EOPNOTSUPP;
> +}
>  static inline int cppc_get_auto_act_window(int cpu, u64 *auto_act_window)
>  {
>  	return -EOPNOTSUPP;

Re: [PATCH v6 1/2] ACPI: CPPC: Add ospm_nominal_perf support

[Christian Loehle]

On 7/27/26 15:01, Christian Loehle wrote:
> On 7/17/26 22:53, Sumit Gupta wrote:
>> Expose the OSPM Nominal Performance register (ACPI 6.6, Section
>> 8.4.6.1.2.6), which conveys the desired nominal performance level
>> at which the platform may run. Unlike the existing read-only
>> Nominal Performance register, it is writable and lets OSPM
>> request a lower nominal level than the platform-reported nominal.
>> The platform classifies performance above this level as boosted
>> and below as throttled for its power/thermal decisions.
>>
>> It is exposed as a per-policy cpufreq sysfs attribute in kHz, to
>> match the cpufreq sysfs unit convention:
>>
>>   /sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq
>>
>> The attribute is documented in
>> Documentation/ABI/testing/sysfs-devices-system-cpu.
>>
>> Writes are converted to perf via cppc_khz_to_perf(), validated
>> against [Lowest Performance, Nominal Performance], and applied to
>> the policy->cpu. The register is assumed shared across the
>> policy->cpus.
>>
>> On read, the current register value is returned, or
>> "<unsupported>" if the platform does not implement the register.
>>
>> Also add the register to the OSPM-set register save/restore
>> table, so its value survives CPU hotplug and reverts to the
>> firmware value on driver unload, like the other registers in
>> the table.
>>
>> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
>> ---
>>  .../ABI/testing/sysfs-devices-system-cpu      | 26 ++++++++++
>>  drivers/acpi/cppc_acpi.c                      | 32 +++++++++++++
>>  drivers/cpufreq/cppc_cpufreq.c                | 47 +++++++++++++++++++
>>  include/acpi/cppc_acpi.h                      | 10 ++++
>>  4 files changed, 115 insertions(+)
>>
>> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
>> index 82d10d556cc8..a8d592c08823 100644
>> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
>> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
>> @@ -346,6 +346,32 @@ Description:	Performance Limited
>>  
>>  		This file is only present if the cppc-cpufreq driver is in use.
>>  
>> +What:		/sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq
>> +Date:		May 2026
>> +Contact:	linux-pm@vger.kernel.org
>> +Description:	OSPM Nominal Performance (kHz)
>> +
>> +		OSPM uses this attribute to request a nominal performance
>> +		level lower than the platform-reported nominal. The
>> +		platform treats performance above this level as boost
>> +		and below as throttle for power and thermal decisions.
>> +
>> +		Read returns the current value in kHz, or "<unsupported>"
>> +		if the platform does not implement the register. Write a
>> +		kHz value in the range [lowest_freq, nominal_freq].
>> +
>> +		Note that tasks may be migrated from one CPU to another
>> +		by the scheduler's load-balancing algorithm, and if
>> +		different OSPM Nominal Performance values are set for
>> +		those CPUs (through different cpufreq policies), that may
>> +		lead to undesirable outcomes. To avoid such issues it is
>> +		better to set the same value across all policies, or to
>> +		pin every task potentially sensitive to it to a specific
>> +		CPU.
>> +
>> +		This file is only present if the cppc-cpufreq driver is
>> +		in use.
>> +
>>  What:		/sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
>>  Date:		August 2008
>>  KernelVersion:	2.6.27
>> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
>> index a7fec6c93178..681d4fd40c11 100644
>> --- a/drivers/acpi/cppc_acpi.c
>> +++ b/drivers/acpi/cppc_acpi.c
>> @@ -1685,6 +1685,38 @@ int cppc_set_epp(int cpu, u64 epp_val)
>>  }
>>  EXPORT_SYMBOL_GPL(cppc_set_epp);
>>  
>> +/**
>> + * cppc_set_ospm_nominal_perf() - Write OSPM Nominal Performance register.
>> + * @cpu: CPU on which to write register.
>> + * @ospm_nominal_perf: Value to write to the OSPM Nominal Performance register.
>> + *
>> + * OSPM Nominal Performance conveys the desired nominal performance level
>> + * at which the platform may run. Per ACPI 6.6, s8.4.6.1.2.6, the value
>> + * must lie within [Lowest Performance, Nominal Performance] and may be
>> + * set independently of Minimum, Maximum and Desired performance. The
>> + * caller is responsible for validating the range.
>> + *
>> + * Return: 0 on success or negative error code.
>> + */
>> +int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
>> +{
>> +	return cppc_set_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
>> +}
>> +EXPORT_SYMBOL_GPL(cppc_set_ospm_nominal_perf);
>> +
>> +/**
>> + * cppc_get_ospm_nominal_perf() - Read OSPM Nominal Performance register.
>> + * @cpu: CPU from which to read register.
>> + * @ospm_nominal_perf: Pointer to store the OSPM Nominal Performance value.
>> + *
>> + * Return: 0 on success or negative error code.
>> + */
>> +int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf)
>> +{
>> +	return cppc_get_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
>> +}
>> +EXPORT_SYMBOL_GPL(cppc_get_ospm_nominal_perf);
> 
> It's a write-only register, we need to track everything in the driver.
> 

So just reread Pierre's comments, TBH I don't see the point of ever
reading it, even for sysfs reads, but I don't think
reading it for cppc_cpufreq_get_effective_nominal() would be valid
in any case?

Re: [PATCH v6 1/2] ACPI: CPPC: Add ospm_nominal_perf support

[Christian Loehle]

On 7/27/26 18:49, Christian Loehle wrote:
> On 7/27/26 15:01, Christian Loehle wrote:
>> On 7/17/26 22:53, Sumit Gupta wrote:
>>> Expose the OSPM Nominal Performance register (ACPI 6.6, Section
>>> 8.4.6.1.2.6), which conveys the desired nominal performance level
>>> at which the platform may run. Unlike the existing read-only
>>> Nominal Performance register, it is writable and lets OSPM
>>> request a lower nominal level than the platform-reported nominal.
>>> The platform classifies performance above this level as boosted
>>> and below as throttled for its power/thermal decisions.
>>>
>>> It is exposed as a per-policy cpufreq sysfs attribute in kHz, to
>>> match the cpufreq sysfs unit convention:
>>>
>>>   /sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq
>>>
>>> The attribute is documented in
>>> Documentation/ABI/testing/sysfs-devices-system-cpu.
>>>
>>> Writes are converted to perf via cppc_khz_to_perf(), validated
>>> against [Lowest Performance, Nominal Performance], and applied to
>>> the policy->cpu. The register is assumed shared across the
>>> policy->cpus.
>>>
>>> On read, the current register value is returned, or
>>> "<unsupported>" if the platform does not implement the register.
>>>
>>> Also add the register to the OSPM-set register save/restore
>>> table, so its value survives CPU hotplug and reverts to the
>>> firmware value on driver unload, like the other registers in
>>> the table.
>>>
>>> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
>>> ---
>>>  .../ABI/testing/sysfs-devices-system-cpu      | 26 ++++++++++
>>>  drivers/acpi/cppc_acpi.c                      | 32 +++++++++++++
>>>  drivers/cpufreq/cppc_cpufreq.c                | 47 +++++++++++++++++++
>>>  include/acpi/cppc_acpi.h                      | 10 ++++
>>>  4 files changed, 115 insertions(+)
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
>>> index 82d10d556cc8..a8d592c08823 100644
>>> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
>>> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
>>> @@ -346,6 +346,32 @@ Description:	Performance Limited
>>>  
>>>  		This file is only present if the cppc-cpufreq driver is in use.
>>>  
>>> +What:		/sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq
>>> +Date:		May 2026
>>> +Contact:	linux-pm@vger.kernel.org
>>> +Description:	OSPM Nominal Performance (kHz)
>>> +
>>> +		OSPM uses this attribute to request a nominal performance
>>> +		level lower than the platform-reported nominal. The
>>> +		platform treats performance above this level as boost
>>> +		and below as throttle for power and thermal decisions.
>>> +
>>> +		Read returns the current value in kHz, or "<unsupported>"
>>> +		if the platform does not implement the register. Write a
>>> +		kHz value in the range [lowest_freq, nominal_freq].
>>> +
>>> +		Note that tasks may be migrated from one CPU to another
>>> +		by the scheduler's load-balancing algorithm, and if
>>> +		different OSPM Nominal Performance values are set for
>>> +		those CPUs (through different cpufreq policies), that may
>>> +		lead to undesirable outcomes. To avoid such issues it is
>>> +		better to set the same value across all policies, or to
>>> +		pin every task potentially sensitive to it to a specific
>>> +		CPU.
>>> +
>>> +		This file is only present if the cppc-cpufreq driver is
>>> +		in use.
>>> +
>>>  What:		/sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
>>>  Date:		August 2008
>>>  KernelVersion:	2.6.27
>>> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
>>> index a7fec6c93178..681d4fd40c11 100644
>>> --- a/drivers/acpi/cppc_acpi.c
>>> +++ b/drivers/acpi/cppc_acpi.c
>>> @@ -1685,6 +1685,38 @@ int cppc_set_epp(int cpu, u64 epp_val)
>>>  }
>>>  EXPORT_SYMBOL_GPL(cppc_set_epp);
>>>  
>>> +/**
>>> + * cppc_set_ospm_nominal_perf() - Write OSPM Nominal Performance register.
>>> + * @cpu: CPU on which to write register.
>>> + * @ospm_nominal_perf: Value to write to the OSPM Nominal Performance register.
>>> + *
>>> + * OSPM Nominal Performance conveys the desired nominal performance level
>>> + * at which the platform may run. Per ACPI 6.6, s8.4.6.1.2.6, the value
>>> + * must lie within [Lowest Performance, Nominal Performance] and may be
>>> + * set independently of Minimum, Maximum and Desired performance. The
>>> + * caller is responsible for validating the range.
>>> + *
>>> + * Return: 0 on success or negative error code.
>>> + */
>>> +int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
>>> +{
>>> +	return cppc_set_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
>>> +}
>>> +EXPORT_SYMBOL_GPL(cppc_set_ospm_nominal_perf);
>>> +
>>> +/**
>>> + * cppc_get_ospm_nominal_perf() - Read OSPM Nominal Performance register.
>>> + * @cpu: CPU from which to read register.
>>> + * @ospm_nominal_perf: Pointer to store the OSPM Nominal Performance value.
>>> + *
>>> + * Return: 0 on success or negative error code.
>>> + */
>>> +int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf)
>>> +{
>>> +	return cppc_get_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
>>> +}
>>> +EXPORT_SYMBOL_GPL(cppc_get_ospm_nominal_perf);
>>
>> It's a write-only register, we need to track everything in the driver.
>>
> 
> So just reread Pierre's comments, TBH I don't see the point of ever
> reading it, even for sysfs reads, but I don't think
> reading it for cppc_cpufreq_get_effective_nominal() would be valid
> in any case?

FWIW desired_perf was read/write up until ACPI 6.5 and only 6.6 marked
it as write-only. I don't think we should be reading it either on
platforms advertising 6.6.
I will clarify and send a patch.

Re: [PATCH v6 1/2] ACPI: CPPC: Add ospm_nominal_perf support

[Zhongqiu Han]

Hello Sumit,

On 7/18/2026 5:53 AM, Sumit Gupta wrote:
> Expose the OSPM Nominal Performance register (ACPI 6.6, Section
> 8.4.6.1.2.6), which conveys the desired nominal performance level
> at which the platform may run. Unlike the existing read-only
> Nominal Performance register, it is writable and lets OSPM
> request a lower nominal level than the platform-reported nominal.
> The platform classifies performance above this level as boosted
> and below as throttled for its power/thermal decisions.
> 
> It is exposed as a per-policy cpufreq sysfs attribute in kHz, to
> match the cpufreq sysfs unit convention:
> 
>    /sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq
> 
> The attribute is documented in
> Documentation/ABI/testing/sysfs-devices-system-cpu.
> 
> Writes are converted to perf via cppc_khz_to_perf(), validated
> against [Lowest Performance, Nominal Performance], and applied to
> the policy->cpu. The register is assumed shared across the
> policy->cpus.
> 
> On read, the current register value is returned, or
> "<unsupported>" if the platform does not implement the register.
> 
> Also add the register to the OSPM-set register save/restore
> table, so its value survives CPU hotplug and reverts to the
> firmware value on driver unload, like the other registers in
> the table.
> 
> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
> ---
>   .../ABI/testing/sysfs-devices-system-cpu      | 26 ++++++++++
>   drivers/acpi/cppc_acpi.c                      | 32 +++++++++++++
>   drivers/cpufreq/cppc_cpufreq.c                | 47 +++++++++++++++++++
>   include/acpi/cppc_acpi.h                      | 10 ++++
>   4 files changed, 115 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> index 82d10d556cc8..a8d592c08823 100644
> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> @@ -346,6 +346,32 @@ Description:	Performance Limited
>   
>   		This file is only present if the cppc-cpufreq driver is in use.
>   
> +What:		/sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq
> +Date:		May 2026
> +Contact:	linux-pm@vger.kernel.org
> +Description:	OSPM Nominal Performance (kHz)
> +
> +		OSPM uses this attribute to request a nominal performance
> +		level lower than the platform-reported nominal. The
> +		platform treats performance above this level as boost
> +		and below as throttle for power and thermal decisions.
> +
> +		Read returns the current value in kHz, or "<unsupported>"
> +		if the platform does not implement the register. Write a
> +		kHz value in the range [lowest_freq, nominal_freq].
> +
> +		Note that tasks may be migrated from one CPU to another
> +		by the scheduler's load-balancing algorithm, and if
> +		different OSPM Nominal Performance values are set for
> +		those CPUs (through different cpufreq policies), that may
> +		lead to undesirable outcomes. To avoid such issues it is
> +		better to set the same value across all policies, or to
> +		pin every task potentially sensitive to it to a specific
> +		CPU.
> +
> +		This file is only present if the cppc-cpufreq driver is
> +		in use.
> +
>   What:		/sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
>   Date:		August 2008
>   KernelVersion:	2.6.27
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index a7fec6c93178..681d4fd40c11 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -1685,6 +1685,38 @@ int cppc_set_epp(int cpu, u64 epp_val)
>   }
>   EXPORT_SYMBOL_GPL(cppc_set_epp);
>   
> +/**
> + * cppc_set_ospm_nominal_perf() - Write OSPM Nominal Performance register.
> + * @cpu: CPU on which to write register.
> + * @ospm_nominal_perf: Value to write to the OSPM Nominal Performance register.
> + *
> + * OSPM Nominal Performance conveys the desired nominal performance level
> + * at which the platform may run. Per ACPI 6.6, s8.4.6.1.2.6, the value
> + * must lie within [Lowest Performance, Nominal Performance] and may be
> + * set independently of Minimum, Maximum and Desired performance. The
> + * caller is responsible for validating the range.
> + *
> + * Return: 0 on success or negative error code.
> + */
> +int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
> +{
> +	return cppc_set_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
> +}
> +EXPORT_SYMBOL_GPL(cppc_set_ospm_nominal_perf);
> +
> +/**
> + * cppc_get_ospm_nominal_perf() - Read OSPM Nominal Performance register.
> + * @cpu: CPU from which to read register.
> + * @ospm_nominal_perf: Pointer to store the OSPM Nominal Performance value.
> + *
> + * Return: 0 on success or negative error code.
> + */
> +int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf)
> +{
> +	return cppc_get_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
> +}
> +EXPORT_SYMBOL_GPL(cppc_get_ospm_nominal_perf);
> +
>   /**
>    * cppc_get_auto_act_window() - Read autonomous activity window register.
>    * @cpu: CPU from which to read register.
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index 9c88512d635c..eb6746810fa6 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -37,6 +37,7 @@ enum cppc_saved_reg_id {
>   	CPPC_SAVED_AUTO_SEL,
>   	CPPC_SAVED_EPP,
>   	CPPC_SAVED_AUTO_ACT_WINDOW,
> +	CPPC_SAVED_OSPM_NOMINAL_PERF,
>   	CPPC_NR_SAVED_REGS,
>   };
>   
> @@ -55,6 +56,9 @@ static const struct cppc_saved_reg cppc_saved_regs[CPPC_NR_SAVED_REGS] = {
>   	[CPPC_SAVED_AUTO_ACT_WINDOW] = {
>   		cppc_get_auto_act_window, cppc_set_auto_act_window,
>   	},
> +	[CPPC_SAVED_OSPM_NOMINAL_PERF] = {
> +		cppc_get_ospm_nominal_perf, cppc_set_ospm_nominal_perf,
> +	},
>   };
>   
>   /*
> @@ -1166,11 +1170,53 @@ static int cppc_get_perf_limited_filtered(int cpu, u64 *perf_limited)
>   CPPC_CPUFREQ_ATTR_RW_U64(perf_limited, cppc_get_perf_limited_filtered,
>   			 cppc_set_perf_limited)
>   
> +static ssize_t show_ospm_nominal_freq(struct cpufreq_policy *policy, char *buf)
> +{
> +	struct cppc_cpudata *cpu_data = policy->driver_data;
> +	u64 perf;
> +	int ret;
> +
> +	ret = cppc_get_ospm_nominal_perf(policy->cpu, &perf);
> +	if (ret == -EOPNOTSUPP)
> +		return sysfs_emit(buf, "<unsupported>\n");
> +	if (ret)
> +		return ret;
> +
> +	return sysfs_emit(buf, "%u\n",
> +			  cppc_perf_to_khz(&cpu_data->perf_caps, perf));

In patch 2/2, cppc_cpufreq_get_effective_nominal() reads the OSPM
Nominal into ospm_nominal via the output pointer of
cppc_get_ospm_nominal_perf(policy->cpu, &ospm_nominal), then checks
ospm_nominal for zero ("A zero value means OSPM has not selected a
nominal level") and substitutes the platform Nominal in that case.

However, show_ospm_nominal_freq() passes the value read through the same
output pointer straight into cppc_perf_to_khz() without the equivalent
zero check. This looks a bit inconsistent — is it intentional, or
should show() apply the same "zero means not selected" handling?


> +}
> +
> +static ssize_t store_ospm_nominal_freq(struct cpufreq_policy *policy,
> +				       const char *buf, size_t count)
> +{
> +	struct cppc_cpudata *cpu_data = policy->driver_data;
> +	unsigned int freq_khz;
> +	u32 perf;
> +	int ret;
> +
> +	ret = kstrtouint(buf, 0, &freq_khz);
> +	if (ret)
> +		return ret;
> +
> +	perf = cppc_khz_to_perf(&cpu_data->perf_caps, freq_khz);
> +	if (perf < cpu_data->perf_caps.lowest_perf ||
> +	    perf > cpu_data->perf_caps.nominal_perf)
> +		return -EINVAL;
> +
> +	/* The register is assumed shared across the policy's CPUs. */
> +	ret = cppc_set_ospm_nominal_perf(policy->cpu, perf);
> +	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(perf_limited);
> +cpufreq_freq_attr_rw(ospm_nominal_freq);
>   
>   static struct freq_attr *cppc_cpufreq_attr[] = {
>   	&freqdomain_cpus,
> @@ -1178,6 +1224,7 @@ static struct freq_attr *cppc_cpufreq_attr[] = {
>   	&auto_act_window,
>   	&energy_performance_preference_val,
>   	&perf_limited,
> +	&ospm_nominal_freq,
>   	NULL,
>   };
>   
> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
> index cd07e1e92bf4..4c9e59643cc0 100644
> --- a/include/acpi/cppc_acpi.h
> +++ b/include/acpi/cppc_acpi.h
> @@ -180,6 +180,8 @@ extern int cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val);
>   extern int cppc_get_epp_perf(int cpunum, u64 *epp_perf);
>   extern int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable);
>   extern int cppc_set_epp(int cpu, u64 epp_val);
> +extern int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf);
> +extern int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf);
>   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);
> @@ -268,6 +270,14 @@ static inline int cppc_set_epp(int cpu, u64 epp_val)
>   {
>   	return -EOPNOTSUPP;
>   }
> +static inline int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
> +{
> +	return -EOPNOTSUPP;
> +}
> +static inline int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf)
> +{
> +	return -EOPNOTSUPP;
> +}
>   static inline int cppc_get_auto_act_window(int cpu, u64 *auto_act_window)
>   {
>   	return -EOPNOTSUPP;


-- 
Thx and BRs,
Zhongqiu Han

Re: [PATCH v6 1/2] ACPI: CPPC: Add ospm_nominal_perf support

[Sumit Gupta]

On 28/07/26 02:53, Christian Loehle wrote:
> External email: Use caution opening links or attachments
>
>
> On 7/27/26 18:49, Christian Loehle wrote:
>> On 7/27/26 15:01, Christian Loehle wrote:
>>> On 7/17/26 22:53, Sumit Gupta wrote:
>>>> Expose the OSPM Nominal Performance register (ACPI 6.6, Section
>>>> 8.4.6.1.2.6), which conveys the desired nominal performance level
>>>> at which the platform may run. Unlike the existing read-only
>>>> Nominal Performance register, it is writable and lets OSPM
>>>> request a lower nominal level than the platform-reported nominal.
>>>> The platform classifies performance above this level as boosted
>>>> and below as throttled for its power/thermal decisions.
>>>>
>>>> It is exposed as a per-policy cpufreq sysfs attribute in kHz, to
>>>> match the cpufreq sysfs unit convention:
>>>>
>>>>    /sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq
>>>>
>>>> The attribute is documented in
>>>> Documentation/ABI/testing/sysfs-devices-system-cpu.
>>>>
>>>> Writes are converted to perf via cppc_khz_to_perf(), validated
>>>> against [Lowest Performance, Nominal Performance], and applied to
>>>> the policy->cpu. The register is assumed shared across the
>>>> policy->cpus.
>>>>
>>>> On read, the current register value is returned, or
>>>> "<unsupported>" if the platform does not implement the register.
>>>>
>>>> Also add the register to the OSPM-set register save/restore
>>>> table, so its value survives CPU hotplug and reverts to the
>>>> firmware value on driver unload, like the other registers in
>>>> the table.
>>>>
>>>> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
>>>> ---
>>>>   .../ABI/testing/sysfs-devices-system-cpu      | 26 ++++++++++
>>>>   drivers/acpi/cppc_acpi.c                      | 32 +++++++++++++
>>>>   drivers/cpufreq/cppc_cpufreq.c                | 47 +++++++++++++++++++
>>>>   include/acpi/cppc_acpi.h                      | 10 ++++
>>>>   4 files changed, 115 insertions(+)
>>>>
>>>> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
>>>> index 82d10d556cc8..a8d592c08823 100644
>>>> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
>>>> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
>>>> @@ -346,6 +346,32 @@ Description:   Performance Limited
>>>>
>>>>              This file is only present if the cppc-cpufreq driver is in use.
>>>>
>>>> +What:              /sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq
>>>> +Date:              May 2026
>>>> +Contact:   linux-pm@vger.kernel.org
>>>> +Description:       OSPM Nominal Performance (kHz)
>>>> +
>>>> +           OSPM uses this attribute to request a nominal performance
>>>> +           level lower than the platform-reported nominal. The
>>>> +           platform treats performance above this level as boost
>>>> +           and below as throttle for power and thermal decisions.
>>>> +
>>>> +           Read returns the current value in kHz, or "<unsupported>"
>>>> +           if the platform does not implement the register. Write a
>>>> +           kHz value in the range [lowest_freq, nominal_freq].
>>>> +
>>>> +           Note that tasks may be migrated from one CPU to another
>>>> +           by the scheduler's load-balancing algorithm, and if
>>>> +           different OSPM Nominal Performance values are set for
>>>> +           those CPUs (through different cpufreq policies), that may
>>>> +           lead to undesirable outcomes. To avoid such issues it is
>>>> +           better to set the same value across all policies, or to
>>>> +           pin every task potentially sensitive to it to a specific
>>>> +           CPU.
>>>> +
>>>> +           This file is only present if the cppc-cpufreq driver is
>>>> +           in use.
>>>> +
>>>>   What:              /sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
>>>>   Date:              August 2008
>>>>   KernelVersion:     2.6.27
>>>> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
>>>> index a7fec6c93178..681d4fd40c11 100644
>>>> --- a/drivers/acpi/cppc_acpi.c
>>>> +++ b/drivers/acpi/cppc_acpi.c
>>>> @@ -1685,6 +1685,38 @@ int cppc_set_epp(int cpu, u64 epp_val)
>>>>   }
>>>>   EXPORT_SYMBOL_GPL(cppc_set_epp);
>>>>
>>>> +/**
>>>> + * cppc_set_ospm_nominal_perf() - Write OSPM Nominal Performance register.
>>>> + * @cpu: CPU on which to write register.
>>>> + * @ospm_nominal_perf: Value to write to the OSPM Nominal Performance register.
>>>> + *
>>>> + * OSPM Nominal Performance conveys the desired nominal performance level
>>>> + * at which the platform may run. Per ACPI 6.6, s8.4.6.1.2.6, the value
>>>> + * must lie within [Lowest Performance, Nominal Performance] and may be
>>>> + * set independently of Minimum, Maximum and Desired performance. The
>>>> + * caller is responsible for validating the range.
>>>> + *
>>>> + * Return: 0 on success or negative error code.
>>>> + */
>>>> +int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
>>>> +{
>>>> +   return cppc_set_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(cppc_set_ospm_nominal_perf);
>>>> +
>>>> +/**
>>>> + * cppc_get_ospm_nominal_perf() - Read OSPM Nominal Performance register.
>>>> + * @cpu: CPU from which to read register.
>>>> + * @ospm_nominal_perf: Pointer to store the OSPM Nominal Performance value.
>>>> + *
>>>> + * Return: 0 on success or negative error code.
>>>> + */
>>>> +int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf)
>>>> +{
>>>> +   return cppc_get_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(cppc_get_ospm_nominal_perf);
>>> It's a write-only register, we need to track everything in the driver.
>>>
>> So just reread Pierre's comments, TBH I don't see the point of ever
>> reading it, even for sysfs reads, but I don't think
>> reading it for cppc_cpufreq_get_effective_nominal() would be valid
>> in any case?
> FWIW desired_perf was read/write up until ACPI 6.5 and only 6.6 marked
> it as write-only. I don't think we should be reading it either on
> platforms advertising 6.6.
> I will clarify and send a patch.

Good catch that ACPI 6.6 makes Desired Performance write-only,
and thanks for the patches preventing those reads.

The same reasoning applies to OSPM Nominal Performance, so I will treat
it as write-only: make ospm_nominal_freq write-only, remove show(), and
drop cppc_get_ospm_nominal_perf().
Boost and policy limits will use the last value the driver successfully
wrote, falling back to the platform reported Nominal Performance when
nothing has been set.

On unload, I will reset it to the platform Nominal Performance only if
the driver wrote it during its lifetime. Otherwise the register is left
untouched, since the pre-driver value cannot be read back.

Thanks,
Sumit

Re: [PATCH v6 1/2] ACPI: CPPC: Add ospm_nominal_perf support

[Sumit Gupta]

Hi Zhongqiu,


On 28/07/26 18:54, Zhongqiu Han wrote:
> External email: Use caution opening links or attachments
>
>
> Hello Sumit,
>
> On 7/18/2026 5:53 AM, Sumit Gupta wrote:
>> Expose the OSPM Nominal Performance register (ACPI 6.6, Section
>> 8.4.6.1.2.6), which conveys the desired nominal performance level
>> at which the platform may run. Unlike the existing read-only
>> Nominal Performance register, it is writable and lets OSPM
>> request a lower nominal level than the platform-reported nominal.
>> The platform classifies performance above this level as boosted
>> and below as throttled for its power/thermal decisions.
>>
>> It is exposed as a per-policy cpufreq sysfs attribute in kHz, to
>> match the cpufreq sysfs unit convention:
>>
>>    /sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq
>>
>> The attribute is documented in
>> Documentation/ABI/testing/sysfs-devices-system-cpu.
>>
>> Writes are converted to perf via cppc_khz_to_perf(), validated
>> against [Lowest Performance, Nominal Performance], and applied to
>> the policy->cpu. The register is assumed shared across the
>> policy->cpus.
>>
>> On read, the current register value is returned, or
>> "<unsupported>" if the platform does not implement the register.
>>
>> Also add the register to the OSPM-set register save/restore
>> table, so its value survives CPU hotplug and reverts to the
>> firmware value on driver unload, like the other registers in
>> the table.
>>
>> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
>> ---
>>   .../ABI/testing/sysfs-devices-system-cpu      | 26 ++++++++++
>>   drivers/acpi/cppc_acpi.c                      | 32 +++++++++++++
>>   drivers/cpufreq/cppc_cpufreq.c                | 47 +++++++++++++++++++
>>   include/acpi/cppc_acpi.h                      | 10 ++++
>>   4 files changed, 115 insertions(+)
>>
>> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu 
>> b/Documentation/ABI/testing/sysfs-devices-system-cpu
>> index 82d10d556cc8..a8d592c08823 100644
>> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
>> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
>> @@ -346,6 +346,32 @@ Description:     Performance Limited
>>
>>               This file is only present if the cppc-cpufreq driver is 
>> in use.
>>
>> +What: /sys/devices/system/cpu/cpuX/cpufreq/ospm_nominal_freq
>> +Date:                May 2026
>> +Contact:     linux-pm@vger.kernel.org
>> +Description: OSPM Nominal Performance (kHz)
>> +
>> +             OSPM uses this attribute to request a nominal performance
>> +             level lower than the platform-reported nominal. The
>> +             platform treats performance above this level as boost
>> +             and below as throttle for power and thermal decisions.
>> +
>> +             Read returns the current value in kHz, or "<unsupported>"
>> +             if the platform does not implement the register. Write a
>> +             kHz value in the range [lowest_freq, nominal_freq].
>> +
>> +             Note that tasks may be migrated from one CPU to another
>> +             by the scheduler's load-balancing algorithm, and if
>> +             different OSPM Nominal Performance values are set for
>> +             those CPUs (through different cpufreq policies), that may
>> +             lead to undesirable outcomes. To avoid such issues it is
>> +             better to set the same value across all policies, or to
>> +             pin every task potentially sensitive to it to a specific
>> +             CPU.
>> +
>> +             This file is only present if the cppc-cpufreq driver is
>> +             in use.
>> +
>>   What: /sys/devices/system/cpu/cpu*/cache/index3/cache_disable_{0,1}
>>   Date:               August 2008
>>   KernelVersion:      2.6.27
>> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
>> index a7fec6c93178..681d4fd40c11 100644
>> --- a/drivers/acpi/cppc_acpi.c
>> +++ b/drivers/acpi/cppc_acpi.c
>> @@ -1685,6 +1685,38 @@ int cppc_set_epp(int cpu, u64 epp_val)
>>   }
>>   EXPORT_SYMBOL_GPL(cppc_set_epp);
>>
>> +/**
>> + * cppc_set_ospm_nominal_perf() - Write OSPM Nominal Performance 
>> register.
>> + * @cpu: CPU on which to write register.
>> + * @ospm_nominal_perf: Value to write to the OSPM Nominal 
>> Performance register.
>> + *
>> + * OSPM Nominal Performance conveys the desired nominal performance 
>> level
>> + * at which the platform may run. Per ACPI 6.6, s8.4.6.1.2.6, the value
>> + * must lie within [Lowest Performance, Nominal Performance] and may be
>> + * set independently of Minimum, Maximum and Desired performance. The
>> + * caller is responsible for validating the range.
>> + *
>> + * Return: 0 on success or negative error code.
>> + */
>> +int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
>> +{
>> +     return cppc_set_reg_val(cpu, OSPM_NOMINAL_PERF, 
>> ospm_nominal_perf);
>> +}
>> +EXPORT_SYMBOL_GPL(cppc_set_ospm_nominal_perf);
>> +
>> +/**
>> + * cppc_get_ospm_nominal_perf() - Read OSPM Nominal Performance 
>> register.
>> + * @cpu: CPU from which to read register.
>> + * @ospm_nominal_perf: Pointer to store the OSPM Nominal Performance 
>> value.
>> + *
>> + * Return: 0 on success or negative error code.
>> + */
>> +int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf)
>> +{
>> +     return cppc_get_reg_val(cpu, OSPM_NOMINAL_PERF, 
>> ospm_nominal_perf);
>> +}
>> +EXPORT_SYMBOL_GPL(cppc_get_ospm_nominal_perf);
>> +
>>   /**
>>    * cppc_get_auto_act_window() - Read autonomous activity window 
>> register.
>>    * @cpu: CPU from which to read register.
>> diff --git a/drivers/cpufreq/cppc_cpufreq.c 
>> b/drivers/cpufreq/cppc_cpufreq.c
>> index 9c88512d635c..eb6746810fa6 100644
>> --- a/drivers/cpufreq/cppc_cpufreq.c
>> +++ b/drivers/cpufreq/cppc_cpufreq.c
>> @@ -37,6 +37,7 @@ enum cppc_saved_reg_id {
>>       CPPC_SAVED_AUTO_SEL,
>>       CPPC_SAVED_EPP,
>>       CPPC_SAVED_AUTO_ACT_WINDOW,
>> +     CPPC_SAVED_OSPM_NOMINAL_PERF,
>>       CPPC_NR_SAVED_REGS,
>>   };
>>
>> @@ -55,6 +56,9 @@ static const struct cppc_saved_reg 
>> cppc_saved_regs[CPPC_NR_SAVED_REGS] = {
>>       [CPPC_SAVED_AUTO_ACT_WINDOW] = {
>>               cppc_get_auto_act_window, cppc_set_auto_act_window,
>>       },
>> +     [CPPC_SAVED_OSPM_NOMINAL_PERF] = {
>> +             cppc_get_ospm_nominal_perf, cppc_set_ospm_nominal_perf,
>> +     },
>>   };
>>
>>   /*
>> @@ -1166,11 +1170,53 @@ static int cppc_get_perf_limited_filtered(int 
>> cpu, u64 *perf_limited)
>>   CPPC_CPUFREQ_ATTR_RW_U64(perf_limited, cppc_get_perf_limited_filtered,
>>                        cppc_set_perf_limited)
>>
>> +static ssize_t show_ospm_nominal_freq(struct cpufreq_policy *policy, 
>> char *buf)
>> +{
>> +     struct cppc_cpudata *cpu_data = policy->driver_data;
>> +     u64 perf;
>> +     int ret;
>> +
>> +     ret = cppc_get_ospm_nominal_perf(policy->cpu, &perf);
>> +     if (ret == -EOPNOTSUPP)
>> +             return sysfs_emit(buf, "<unsupported>\n");
>> +     if (ret)
>> +             return ret;
>> +
>> +     return sysfs_emit(buf, "%u\n",
>> + cppc_perf_to_khz(&cpu_data->perf_caps, perf));
>
> In patch 2/2, cppc_cpufreq_get_effective_nominal() reads the OSPM
> Nominal into ospm_nominal via the output pointer of
> cppc_get_ospm_nominal_perf(policy->cpu, &ospm_nominal), then checks
> ospm_nominal for zero ("A zero value means OSPM has not selected a
> nominal level") and substitutes the platform Nominal in that case.
>
> However, show_ospm_nominal_freq() passes the value read through the same
> output pointer straight into cppc_perf_to_khz() without the equivalent
> zero check. This looks a bit inconsistent — is it intentional, or
> should show() apply the same "zero means not selected" handling?
>

Thanks for pointing this out.
In v7, I will make ospm_nominal_freq as write-only and remove sysfs
show() and cppc_get_ospm_nominal_perf(), eliminating this inconsistency.
The effective nominal calculation will use the last successfully
written value, falling back to the platform Nominal Performance if none
has been written.

Thanks,
Sumit


>
>> +}
>> +
>> +static ssize_t store_ospm_nominal_freq(struct cpufreq_policy *policy,
>> +                                    const char *buf, size_t count)
>> +{
>> +     struct cppc_cpudata *cpu_data = policy->driver_data;
>> +     unsigned int freq_khz;
>> +     u32 perf;
>> +     int ret;
>> +
>> +     ret = kstrtouint(buf, 0, &freq_khz);
>> +     if (ret)
>> +             return ret;
>> +
>> +     perf = cppc_khz_to_perf(&cpu_data->perf_caps, freq_khz);
>> +     if (perf < cpu_data->perf_caps.lowest_perf ||
>> +         perf > cpu_data->perf_caps.nominal_perf)
>> +             return -EINVAL;
>> +
>> +     /* The register is assumed shared across the policy's CPUs. */
>> +     ret = cppc_set_ospm_nominal_perf(policy->cpu, perf);
>> +     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(perf_limited);
>> +cpufreq_freq_attr_rw(ospm_nominal_freq);
>>
>>   static struct freq_attr *cppc_cpufreq_attr[] = {
>>       &freqdomain_cpus,
>> @@ -1178,6 +1224,7 @@ static struct freq_attr *cppc_cpufreq_attr[] = {
>>       &auto_act_window,
>>       &energy_performance_preference_val,
>>       &perf_limited,
>> +     &ospm_nominal_freq,
>>       NULL,
>>   };
>>
>> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
>> index cd07e1e92bf4..4c9e59643cc0 100644
>> --- a/include/acpi/cppc_acpi.h
>> +++ b/include/acpi/cppc_acpi.h
>> @@ -180,6 +180,8 @@ extern int cpc_write_ffh(int cpunum, struct 
>> cpc_reg *reg, u64 val);
>>   extern int cppc_get_epp_perf(int cpunum, u64 *epp_perf);
>>   extern int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls 
>> *perf_ctrls, bool enable);
>>   extern int cppc_set_epp(int cpu, u64 epp_val);
>> +extern int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf);
>> +extern int cppc_get_ospm_nominal_perf(int cpu, u64 *ospm_nominal_perf);
>>   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);
>> @@ -268,6 +270,14 @@ static inline int cppc_set_epp(int cpu, u64 
>> epp_val)
>>   {
>>       return -EOPNOTSUPP;
>>   }
>> +static inline int cppc_set_ospm_nominal_perf(int cpu, u64 
>> ospm_nominal_perf)
>> +{
>> +     return -EOPNOTSUPP;
>> +}
>> +static inline int cppc_get_ospm_nominal_perf(int cpu, u64 
>> *ospm_nominal_perf)
>> +{
>> +     return -EOPNOTSUPP;
>> +}
>>   static inline int cppc_get_auto_act_window(int cpu, u64 
>> *auto_act_window)
>>   {
>>       return -EOPNOTSUPP;
>
>
> -- 
> Thx and BRs,
> Zhongqiu Han