[PATCH v2 0/2] ACPI: CPPC: Add CPPC v4 support (ACPI 6.6)

[PATCH v2 0/2] ACPI: CPPC: Add CPPC v4 support (ACPI 6.6)

[Sumit Gupta]

Add initial kernel support for CPPC v4 (ACPI 6.6, Section 8.4.6),
which extends the _CPC package from 23 to 25 entries with two
optional fields:

  - OSPM Nominal Performance (8.4.6.1.2.6): register used by OSPM
    to tell the platform what it considers nominal. The platform
    classifies performance above this as boost and below as
    throttle for power/thermal decisions.

  - Resource Priority (8.4.6.1.2.7): Package of Resource Priority
    Register Descriptor sub-packages. Full parsing is not yet
    implemented; such entries are marked as unsupported.

Patch 1: Add v4 _CPC parsing - validate the 25-entry layout,
handle the Resource Priority package, and mark the two new
registers optional.

Patch 2: Add acpi_cppc/ospm_nominal_perf as a read-write sysfs
attribute, and initialize it to the platform nominal value
during cppc_cpufreq policy init.

---
v1[1] -> v2:
- Patch 1: added Reviewed-by from Mario Limonciello.
- Patch 2:
  - Make ospm_nominal_perf sysfs read-write; cache last write in
    cpc_desc and skip redundant register writes.
  - Validate input in cppc_set_ospm_nominal_perf.

Sumit Gupta (2):
  ACPI: CPPC: Add support for CPPC v4
  ACPI: CPPC: Add ospm_nominal_perf support

 drivers/acpi/cppc_acpi.c       | 93 +++++++++++++++++++++++++++++++---
 drivers/cpufreq/cppc_cpufreq.c | 10 ++++
 include/acpi/cppc_acpi.h       | 14 ++++-
 3 files changed, 109 insertions(+), 8 deletions(-)

[1] https://lore.kernel.org/lkml/20260427051823.280419-1-sumitg@nvidia.com/

-- 
2.34.1

[PATCH v2 1/2] ACPI: CPPC: Add support for CPPC v4

[Sumit Gupta]

CPPC v4 (ACPI 6.6, Section 8.4.6) adds two optional entries to the
_CPC package:

1. OSPM Nominal Performance (8.4.6.1.2.6): A write-only register that
   lets OSPM inform the platform what it considers nominal performance.
   The platform classifies performance above this level as boost and
   below as throttle for its power/thermal decisions.

2. Resource Priority (8.4.6.1.2.7): A Package of Resource Priority
   Register Descriptor sub-packages that allow OSPM to set relative
   priority among processors for shared resources (boost, throttle,
   L2/L3 cache, memory bandwidth). Parsing the full structure is not
   yet supported; such entries are marked as unsupported.

Add v4 _CPC table parsing (25 entries) and update REG_OPTIONAL to
mark the two new registers as optional.

Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
---
 drivers/acpi/cppc_acpi.c | 24 ++++++++++++++++++------
 include/acpi/cppc_acpi.h |  8 ++++++--
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 2e91c5a97761..a1c91ce20cc8 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -134,7 +134,7 @@ static DEFINE_PER_CPU(struct cpc_desc *, cpc_desc_ptr);
  * cpc_regs[] with the corresponding index. 0 means mandatory and 1
  * means optional.
  */
-#define REG_OPTIONAL (0x1FC7D0)
+#define REG_OPTIONAL (0x7FC7D0)
 
 /*
  * Use the index of the register in per-cpu cpc_regs[] to check if
@@ -751,18 +751,19 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
 	/*
 	 * Disregard _CPC if the number of entries in the return package is not
 	 * as expected, but support future revisions being proper supersets of
-	 * the v3 and only causing more entries to be returned by _CPC.
+	 * the v4 and only causing more entries to be returned by _CPC.
 	 */
 	if ((cpc_rev == CPPC_V2_REV && num_ent != CPPC_V2_NUM_ENT) ||
 	    (cpc_rev == CPPC_V3_REV && num_ent != CPPC_V3_NUM_ENT) ||
-	    (cpc_rev > CPPC_V3_REV && num_ent <= CPPC_V3_NUM_ENT)) {
+	    (cpc_rev == CPPC_V4_REV && num_ent != CPPC_V4_NUM_ENT) ||
+	    (cpc_rev > CPPC_V4_REV && num_ent <= CPPC_V4_NUM_ENT)) {
 		pr_debug("Unexpected number of _CPC return package entries (%d) for CPU:%d\n",
 			 num_ent, pr->id);
 		goto out_free;
 	}
-	if (cpc_rev > CPPC_V3_REV) {
-		num_ent = CPPC_V3_NUM_ENT;
-		cpc_rev = CPPC_V3_REV;
+	if (cpc_rev > CPPC_V4_REV) {
+		num_ent = CPPC_V4_NUM_ENT;
+		cpc_rev = CPPC_V4_REV;
 	}
 
 	cpc_ptr->num_entries = num_ent;
@@ -845,6 +846,17 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
 
 			cpc_ptr->cpc_regs[i-2].type = ACPI_TYPE_BUFFER;
 			memcpy(&cpc_ptr->cpc_regs[i-2].cpc_entry.reg, gas_t, sizeof(*gas_t));
+		} else if (cpc_obj->type == ACPI_TYPE_PACKAGE) {
+			/*
+			 * ACPI 6.6, s8.4.6.1.2.7 defines Resource Priority
+			 * as a Package of Resource Priority Register Descriptor
+			 * sub-packages.  Parsing the full structure is not yet
+			 * supported; mark the register as unsupported for now.
+			 */
+			pr_debug("CPU:%d entry %d: package type not supported\n",
+				 pr->id, i);
+			cpc_ptr->cpc_regs[i-2].type = ACPI_TYPE_INTEGER;
+			cpc_ptr->cpc_regs[i-2].cpc_entry.int_value = 0;
 		} else {
 			pr_debug("Invalid entry type (%d) in _CPC for CPU:%d\n",
 				 i, pr->id);
diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index d1f02ceec4f9..8693890a7275 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -17,16 +17,18 @@
 #include <acpi/pcc.h>
 #include <acpi/processor.h>
 
-/* CPPCv2 and CPPCv3 support */
+/* CPPCv2, CPPCv3 and CPPCv4 support */
 #define CPPC_V2_REV	2
 #define CPPC_V3_REV	3
+#define CPPC_V4_REV	4
 #define CPPC_V2_NUM_ENT	21
 #define CPPC_V3_NUM_ENT	23
+#define CPPC_V4_NUM_ENT	25
 
 #define PCC_CMD_COMPLETE_MASK	(1 << 0)
 #define PCC_ERROR_MASK		(1 << 2)
 
-#define MAX_CPC_REG_ENT 21
+#define MAX_CPC_REG_ENT 23
 
 /* CPPC specific PCC commands. */
 #define	CMD_READ 0
@@ -109,6 +111,8 @@ enum cppc_regs {
 	REFERENCE_PERF,
 	LOWEST_FREQ,
 	NOMINAL_FREQ,
+	OSPM_NOMINAL_PERF,
+	RESOURCE_PRIORITY,
 };
 
 /*
-- 
2.34.1

Re: [PATCH v2 1/2] ACPI: CPPC: Add support for CPPC v4

[Pierre Gondois]

Hello Sumit,

On 4/30/26 16:24, Sumit Gupta wrote:
> CPPC v4 (ACPI 6.6, Section 8.4.6) adds two optional entries to the
> _CPC package:
>
> 1. OSPM Nominal Performance (8.4.6.1.2.6): A write-only register that
>     lets OSPM inform the platform what it considers nominal performance.
>     The platform classifies performance above this level as boost and
>     below as throttle for its power/thermal decisions.
>
> 2. Resource Priority (8.4.6.1.2.7): A Package of Resource Priority
>     Register Descriptor sub-packages that allow OSPM to set relative
>     priority among processors for shared resources (boost, throttle,
>     L2/L3 cache, memory bandwidth). Parsing the full structure is not
>     yet supported; such entries are marked as unsupported.
>
> Add v4 _CPC table parsing (25 entries) and update REG_OPTIONAL to
> mark the two new registers as optional.
>
> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
> Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>

Reviewed-by: Pierre Gondois <pierre.gondois@arm.com>

[PATCH v2 2/2] ACPI: CPPC: Add ospm_nominal_perf support

[Sumit Gupta]

Add acpi_cppc/ospm_nominal_perf sysfs attribute (read-write) and
cppc_set_ospm_nominal_perf() API for the OSPM Nominal Performance
register (ACPI 6.6, Section 8.4.6.1.2.6).

The register conveys the desired nominal performance level at which
the platform may run. OSPM can request a lower level than platform
nominal. Valid range is [Lowest Performance, Nominal Performance].
The value tells the platform what OSPM considers nominal. The
platform classifies performance above this as boosted and below as
throttled. It uses that for its power/thermal decisions.

Although the register is write-only per spec, cache the OSPM-written
value in cpc_desc so userspace can observe it via sysfs, and to
skip redundant writes.

Initialize to platform nominal at policy init. Override via sysfs
if needed.

Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
---
 drivers/acpi/cppc_acpi.c       | 69 ++++++++++++++++++++++++++++++++++
 drivers/cpufreq/cppc_cpufreq.c | 10 +++++
 include/acpi/cppc_acpi.h       |  6 +++
 3 files changed, 85 insertions(+)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index a1c91ce20cc8..fbc620adafad 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -155,6 +155,10 @@ static DEFINE_PER_CPU(struct cpc_desc *, cpc_desc_ptr);
 static struct kobj_attribute _name =		\
 __ATTR(_name, 0444, show_##_name, NULL)
 
+#define define_one_cppc_rw(_name)		\
+static struct kobj_attribute _name =		\
+__ATTR(_name, 0644, show_##_name, store_##_name)
+
 #define to_cpc_desc(a) container_of(a, struct cpc_desc, kobj)
 
 #define show_cppc_data(access_fn, struct_name, member_name)		\
@@ -211,6 +215,38 @@ static ssize_t show_feedback_ctrs(struct kobject *kobj,
 }
 define_one_cppc_ro(feedback_ctrs);
 
+static ssize_t show_ospm_nominal_perf(struct kobject *kobj,
+				      struct kobj_attribute *attr, char *buf)
+{
+	struct cpc_desc *cpc_ptr = to_cpc_desc(kobj);
+	u64 val = READ_ONCE(cpc_ptr->ospm_nominal_perf);
+
+	if (!val)
+		return -ENODATA;
+
+	return sysfs_emit(buf, "%llu\n", val);
+}
+
+static ssize_t store_ospm_nominal_perf(struct kobject *kobj,
+				       struct kobj_attribute *attr,
+				       const char *buf, size_t count)
+{
+	struct cpc_desc *cpc_ptr = to_cpc_desc(kobj);
+	u64 val;
+	int ret;
+
+	ret = kstrtou64(buf, 0, &val);
+	if (ret)
+		return ret;
+
+	ret = cppc_set_ospm_nominal_perf(cpc_ptr->cpu_id, val);
+	if (ret)
+		return ret;
+
+	return count;
+}
+define_one_cppc_rw(ospm_nominal_perf);
+
 static struct attribute *cppc_attrs[] = {
 	&feedback_ctrs.attr,
 	&reference_perf.attr,
@@ -222,6 +258,7 @@ static struct attribute *cppc_attrs[] = {
 	&nominal_perf.attr,
 	&nominal_freq.attr,
 	&lowest_freq.attr,
+	&ospm_nominal_perf.attr,
 	NULL
 };
 ATTRIBUTE_GROUPS(cppc);
@@ -1683,6 +1720,38 @@ 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 allows OSPM to inform the platform of the nominal
+ * performance level it intends to maintain.
+ *
+ * Return: 0 for success, -EINVAL on invalid input, -EOPNOTSUPP if not
+ * supported, -EIO otherwise.
+ */
+int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
+{
+	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
+	int ret;
+
+	if (!ospm_nominal_perf || ospm_nominal_perf > U32_MAX)
+		return -EINVAL;
+
+	if (cpc_desc &&
+	    READ_ONCE(cpc_desc->ospm_nominal_perf) == ospm_nominal_perf)
+		return 0;
+
+	ret = cppc_set_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
+	if (ret)
+		return ret;
+
+	WRITE_ONCE(cpc_desc->ospm_nominal_perf, ospm_nominal_perf);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(cppc_set_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 7e7f9dfb7a24..d06cba963550 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -715,6 +715,16 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
 		goto out;
 	}
 
+	/*
+	 * Initialize OSPM Nominal Performance to inform firmware of
+	 * OSPM's nominal level. Performance above this value = boost;
+	 * below = throttle. Uses platform nominal by default.
+	 */
+	ret = cppc_set_ospm_nominal_perf(cpu, caps->nominal_perf);
+	if (ret && ret != -EOPNOTSUPP)
+		pr_debug("Failed to set ospm_nominal_perf for CPU%d: %d\n",
+			 cpu, ret);
+
 	cppc_cpufreq_cpu_fie_init(policy);
 	return 0;
 
diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index 8693890a7275..3771e2ed507d 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -86,6 +86,7 @@ struct cpc_desc {
 	struct cpc_register_resource cpc_regs[MAX_CPC_REG_ENT];
 	struct acpi_psd_package domain_info;
 	struct kobject kobj;
+	u32 ospm_nominal_perf;
 };
 
 /* These are indexes into the per-cpu cpc_regs[]. Order is important. */
@@ -180,6 +181,7 @@ 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_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);
@@ -266,6 +268,10 @@ 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_auto_act_window(int cpu, u64 *auto_act_window)
 {
 	return -EOPNOTSUPP;
-- 
2.34.1

Re: [PATCH v2 2/2] ACPI: CPPC: Add ospm_nominal_perf support

[Mario Limonciello]

On 4/30/26 09:24, Sumit Gupta wrote:
> Add acpi_cppc/ospm_nominal_perf sysfs attribute (read-write) and
> cppc_set_ospm_nominal_perf() API for the OSPM Nominal Performance
> register (ACPI 6.6, Section 8.4.6.1.2.6).
> 
> The register conveys the desired nominal performance level at which
> the platform may run. OSPM can request a lower level than platform
> nominal. Valid range is [Lowest Performance, Nominal Performance].
> The value tells the platform what OSPM considers nominal. The
> platform classifies performance above this as boosted and below as
> throttled. It uses that for its power/thermal decisions.
> 
> Although the register is write-only per spec, cache the OSPM-written
> value in cpc_desc so userspace can observe it via sysfs, and to
> skip redundant writes.
> 
> Initialize to platform nominal at policy init. Override via sysfs
> if needed.
> 
> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
> ---
>   drivers/acpi/cppc_acpi.c       | 69 ++++++++++++++++++++++++++++++++++
>   drivers/cpufreq/cppc_cpufreq.c | 10 +++++
>   include/acpi/cppc_acpi.h       |  6 +++
>   3 files changed, 85 insertions(+)
> 
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index a1c91ce20cc8..fbc620adafad 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -155,6 +155,10 @@ static DEFINE_PER_CPU(struct cpc_desc *, cpc_desc_ptr);
>   static struct kobj_attribute _name =		\
>   __ATTR(_name, 0444, show_##_name, NULL)
>   
> +#define define_one_cppc_rw(_name)		\
> +static struct kobj_attribute _name =		\
> +__ATTR(_name, 0644, show_##_name, store_##_name)
> +
>   #define to_cpc_desc(a) container_of(a, struct cpc_desc, kobj)
>   
>   #define show_cppc_data(access_fn, struct_name, member_name)		\
> @@ -211,6 +215,38 @@ static ssize_t show_feedback_ctrs(struct kobject *kobj,
>   }
>   define_one_cppc_ro(feedback_ctrs);
>   
> +static ssize_t show_ospm_nominal_perf(struct kobject *kobj,
> +				      struct kobj_attribute *attr, char *buf)
> +{
> +	struct cpc_desc *cpc_ptr = to_cpc_desc(kobj);
> +	u64 val = READ_ONCE(cpc_ptr->ospm_nominal_perf);
> +
> +	if (!val)
> +		return -ENODATA;
> +
> +	return sysfs_emit(buf, "%llu\n", val);
> +}
> +
> +static ssize_t store_ospm_nominal_perf(struct kobject *kobj,
> +				       struct kobj_attribute *attr,
> +				       const char *buf, size_t count)
> +{
> +	struct cpc_desc *cpc_ptr = to_cpc_desc(kobj);
> +	u64 val;
> +	int ret;
> +
> +	ret = kstrtou64(buf, 0, &val);
> +	if (ret)
> +		return ret;
> +
> +	ret = cppc_set_ospm_nominal_perf(cpc_ptr->cpu_id, val);
> +	if (ret)
> +		return ret;
> +
> +	return count;
> +}
> +define_one_cppc_rw(ospm_nominal_perf);
> +
>   static struct attribute *cppc_attrs[] = {
>   	&feedback_ctrs.attr,
>   	&reference_perf.attr,
> @@ -222,6 +258,7 @@ static struct attribute *cppc_attrs[] = {
>   	&nominal_perf.attr,
>   	&nominal_freq.attr,
>   	&lowest_freq.attr,
> +	&ospm_nominal_perf.attr,
>   	NULL
>   };
>   ATTRIBUTE_GROUPS(cppc);
> @@ -1683,6 +1720,38 @@ 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 allows OSPM to inform the platform of the nominal
> + * performance level it intends to maintain.
> + *
> + * Return: 0 for success, -EINVAL on invalid input, -EOPNOTSUPP if not
> + * supported, -EIO otherwise.
> + */
> +int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
> +{
> +	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
> +	int ret;
> +
> +	if (!ospm_nominal_perf || ospm_nominal_perf > U32_MAX)
> +		return -EINVAL;
> +
> +	if (cpc_desc &&
> +	    READ_ONCE(cpc_desc->ospm_nominal_perf) == ospm_nominal_perf)
> +		return 0;
> +
> +	ret = cppc_set_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
> +	if (ret)
> +		return ret;
> +
> +	WRITE_ONCE(cpc_desc->ospm_nominal_perf, ospm_nominal_perf);
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(cppc_set_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 7e7f9dfb7a24..d06cba963550 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -715,6 +715,16 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
>   		goto out;
>   	}
>   
> +	/*
> +	 * Initialize OSPM Nominal Performance to inform firmware of
> +	 * OSPM's nominal level. Performance above this value = boost;
> +	 * below = throttle. Uses platform nominal by default.
> +	 */
> +	ret = cppc_set_ospm_nominal_perf(cpu, caps->nominal_perf);
> +	if (ret && ret != -EOPNOTSUPP)
> +		pr_debug("Failed to set ospm_nominal_perf for CPU%d: %d\n",
> +			 cpu, ret);
> +
>   	cppc_cpufreq_cpu_fie_init(policy);
>   	return 0;
>   
> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
> index 8693890a7275..3771e2ed507d 100644
> --- a/include/acpi/cppc_acpi.h
> +++ b/include/acpi/cppc_acpi.h
> @@ -86,6 +86,7 @@ struct cpc_desc {
>   	struct cpc_register_resource cpc_regs[MAX_CPC_REG_ENT];
>   	struct acpi_psd_package domain_info;
>   	struct kobject kobj;
> +	u32 ospm_nominal_perf;
>   };
>   
>   /* These are indexes into the per-cpu cpc_regs[]. Order is important. */
> @@ -180,6 +181,7 @@ 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_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);
> @@ -266,6 +268,10 @@ 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_auto_act_window(int cpu, u64 *auto_act_window)
>   {
>   	return -EOPNOTSUPP;

Re: [PATCH v2 2/2] ACPI: CPPC: Add ospm_nominal_perf support

[Pierre Gondois]

Hello Sumit,

On 4/30/26 16:24, Sumit Gupta wrote:
> Add acpi_cppc/ospm_nominal_perf sysfs attribute (read-write) and
> cppc_set_ospm_nominal_perf() API for the OSPM Nominal Performance
> register (ACPI 6.6, Section 8.4.6.1.2.6).
>
> The register conveys the desired nominal performance level at which
> the platform may run. OSPM can request a lower level than platform
> nominal. Valid range is [Lowest Performance, Nominal Performance].
> The value tells the platform what OSPM considers nominal. The
> platform classifies performance above this as boosted and below as
> throttled. It uses that for its power/thermal decisions.
>
> Although the register is write-only per spec, cache the OSPM-written
> value in cpc_desc so userspace can observe it via sysfs, and to
> skip redundant writes.
>
> Initialize to platform nominal at policy init. Override via sysfs
> if needed.
>
> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
> ---
>   drivers/acpi/cppc_acpi.c       | 69 ++++++++++++++++++++++++++++++++++
>   drivers/cpufreq/cppc_cpufreq.c | 10 +++++
>   include/acpi/cppc_acpi.h       |  6 +++
>   3 files changed, 85 insertions(+)
>
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index a1c91ce20cc8..fbc620adafad 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -155,6 +155,10 @@ static DEFINE_PER_CPU(struct cpc_desc *, cpc_desc_ptr);
>   static struct kobj_attribute _name =		\
>   __ATTR(_name, 0444, show_##_name, NULL)
>   
> +#define define_one_cppc_rw(_name)		\
> +static struct kobj_attribute _name =		\
> +__ATTR(_name, 0644, show_##_name, store_##_name)
> +
>   #define to_cpc_desc(a) container_of(a, struct cpc_desc, kobj)
>   
>   #define show_cppc_data(access_fn, struct_name, member_name)		\
> @@ -211,6 +215,38 @@ static ssize_t show_feedback_ctrs(struct kobject *kobj,
>   }
>   define_one_cppc_ro(feedback_ctrs);
>   
> +static ssize_t show_ospm_nominal_perf(struct kobject *kobj,
> +				      struct kobj_attribute *attr, char *buf)
> +{
> +	struct cpc_desc *cpc_ptr = to_cpc_desc(kobj);
> +	u64 val = READ_ONCE(cpc_ptr->ospm_nominal_perf);
> +
> +	if (!val)
> +		return -ENODATA;
> +
> +	return sysfs_emit(buf, "%llu\n", val);
> +}
> +
> +static ssize_t store_ospm_nominal_perf(struct kobject *kobj,
> +				       struct kobj_attribute *attr,
> +				       const char *buf, size_t count)
> +{
> +	struct cpc_desc *cpc_ptr = to_cpc_desc(kobj);
> +	u64 val;
> +	int ret;
> +
> +	ret = kstrtou64(buf, 0, &val);
> +	if (ret)
> +		return ret;
> +
> +	ret = cppc_set_ospm_nominal_perf(cpc_ptr->cpu_id, val);
> +	if (ret)
> +		return ret;
> +
> +	return count;
> +}
> +define_one_cppc_rw(ospm_nominal_perf);
> +
>   static struct attribute *cppc_attrs[] = {
>   	&feedback_ctrs.attr,
>   	&reference_perf.attr,
> @@ -222,6 +258,7 @@ static struct attribute *cppc_attrs[] = {
>   	&nominal_perf.attr,
>   	&nominal_freq.attr,
>   	&lowest_freq.attr,
> +	&ospm_nominal_perf.attr,
>   	NULL
>   };
>   ATTRIBUTE_GROUPS(cppc);
> @@ -1683,6 +1720,38 @@ 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 allows OSPM to inform the platform of the nominal
> + * performance level it intends to maintain.
> + *
> + * Return: 0 for success, -EINVAL on invalid input, -EOPNOTSUPP if not
> + * supported, -EIO otherwise.
> + */
> +int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
> +{
> +	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
> +	int ret;
> +
> +	if (!ospm_nominal_perf || ospm_nominal_perf > U32_MAX)
> +		return -EINVAL;
I think the spec also requests to have a value in the range

[lowest:nominal]. As these registers are read-only it should

be ok to read the values here ?

> +
> +	if (cpc_desc &&
> +	    READ_ONCE(cpc_desc->ospm_nominal_perf) == ospm_nominal_perf)
> +		return 0;
> +
> +	ret = cppc_set_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
> +	if (ret)
> +		return ret;
> +

Shouldn't we have some protection against concurrent accesses ?

> +	WRITE_ONCE(cpc_desc->ospm_nominal_perf, ospm_nominal_perf);
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(cppc_set_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 7e7f9dfb7a24..d06cba963550 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -715,6 +715,16 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
>   		goto out;
>   	}
>   
> +	/*
> +	 * Initialize OSPM Nominal Performance to inform firmware of
> +	 * OSPM's nominal level. Performance above this value = boost;
> +	 * below = throttle. Uses platform nominal by default.
> +	 */
> +	ret = cppc_set_ospm_nominal_perf(cpu, caps->nominal_perf);
> +	if (ret && ret != -EOPNOTSUPP)
> +		pr_debug("Failed to set ospm_nominal_perf for CPU%d: %d\n",
> +			 cpu, ret);
> +

IIUC, if (ospm_nominal_perf == nominal_perf), the firmware should
not behave differently. Is this really useful ?

------------

Also this seems like there will need some synchronization
mechanism to keep-up with the boost state.

If the ospm_nominal_perf is lowered and boost is disabled,
a freq. update should happen. IMO it looks like this could
be handled with (another) freq_qos_request.

This new freq_qos_request, if we name it ospm_nominal_freq_req,
should only be taken into account if boost is disabled.
Otherwise, if boost is enabled, ospm_nominal_freq_req
should be ignored.

------------

Also, the function seems to set the ospm_nominal_freq for
a single CPU when the policy might be common for multiple
CPUs right ?

The issues this field raises seems similar to the auto_sel
ones. I.e. :

- concurrency accesses + need for a scratch value

- what should happen when unloading the driver

- the value can be set for single CPUs but we might
want to have the same value for the whole policy

Maybe a common solution should be found.
(I m not suggesting anything right now unfortunately).


>   	cppc_cpufreq_cpu_fie_init(policy);
>   	return 0;
>   
> diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
> index 8693890a7275..3771e2ed507d 100644
> --- a/include/acpi/cppc_acpi.h
> +++ b/include/acpi/cppc_acpi.h
> @@ -86,6 +86,7 @@ struct cpc_desc {
>   	struct cpc_register_resource cpc_regs[MAX_CPC_REG_ENT];
>   	struct acpi_psd_package domain_info;
>   	struct kobject kobj;
> +	u32 ospm_nominal_perf;
>   };
>   
>   /* These are indexes into the per-cpu cpc_regs[]. Order is important. */
> @@ -180,6 +181,7 @@ 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_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);
> @@ -266,6 +268,10 @@ 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_auto_act_window(int cpu, u64 *auto_act_window)
>   {
>   	return -EOPNOTSUPP;