[PATCH v3 0/2] ACPI: CPPC: Add CPPC v4 support (ACPI 6.6)

[PATCH v3 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,
restrict the Resource Priority package fallback to that slot
only, and mark the two new registers optional.

Patch 2: Add per-policy sysfs attribute ospm_nominal_freq (kHz)
under cpufreq. Writes are converted to perf and applied to every
CPU in policy->cpus.

---
v2[2] -> v3:
- Patch 1:
  - Accept ACPI_TYPE_PACKAGE only at RESOURCE_PRIORITY; abort otherwise.
  - Added Reviewed-by from Pierre Gondois.
- Patch 2:
  - Sysfs moved from per-CPU acpi_cppc to per-policy cpufreq.
  - Read ospm_nominal_freq sysfs input in kHz and convert to perf.
  - Cached ospm_nominal_perf moved from cpc_desc to cppc_cpudata.
  - Validate input against [Lowest Performance, Nominal Performance]
    in cppc_set_ospm_nominal_perf().
  - Dropped unconditional init in cppc_cpufreq_cpu_init().
  - Remove to skip write if cache matches in cppc_set_ospm_nominal_perf.
  - Early -ENODEV return when no CPC descriptor.
  - Added ABI documentation at
    Documentation/ABI/testing/sysfs-devices-system-cpu.

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

 .../ABI/testing/sysfs-devices-system-cpu      | 17 ++++++
 drivers/acpi/cppc_acpi.c                      | 58 +++++++++++++++++--
 drivers/cpufreq/cppc_cpufreq.c                | 40 +++++++++++++
 include/acpi/cppc_acpi.h                      | 15 ++++-
 4 files changed, 122 insertions(+), 8 deletions(-)

[1] https://lore.kernel.org/lkml/20260427051823.280419-1-sumitg@nvidia.com/
[2] https://lore.kernel.org/lkml/20260430142430.755437-1-sumitg@nvidia.com/

-- 
2.34.1

[PATCH v3 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>
Reviewed-by: Pierre Gondois <pierre.gondois@arm.com>
---
 drivers/acpi/cppc_acpi.c | 23 +++++++++++++++++------
 include/acpi/cppc_acpi.h |  8 ++++++--
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index f370be8715ae..c76cfafa3589 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 +846,16 @@ 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 && (i - 2) == RESOURCE_PRIORITY) {
+			/*
+			 * 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 Resource Priority not supported\n", pr->id);
+			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

[PATCH v3 2/2] 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/cpufreq/policyN/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
every CPU in policy->cpus.

The register is write-only; the kernel caches the last written
value in struct cppc_cpudata for sysfs readback (returns 0 until
userspace writes a value).

Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
---
 .../ABI/testing/sysfs-devices-system-cpu      | 17 ++++++++
 drivers/acpi/cppc_acpi.c                      | 35 ++++++++++++++++
 drivers/cpufreq/cppc_cpufreq.c                | 40 +++++++++++++++++++
 include/acpi/cppc_acpi.h                      |  7 ++++
 4 files changed, 99 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index 82d10d556cc8..ac1bf1b89ac4 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -346,6 +346,23 @@ 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 last written value in kHz, or 0 if no
+		value has been written. Write a kHz value in the range
+		[lowest_freq, nominal_freq].
+
+		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 c76cfafa3589..ad6ece16c30d 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1682,6 +1682,41 @@ 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.
+ *
+ * Return: 0 on success or negative error code.
+ */
+int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
+{
+	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
+	struct cppc_perf_caps caps;
+	int ret;
+
+	if (!cpc_desc) {
+		pr_debug("No CPC descriptor for CPU:%d\n", cpu);
+		return -ENODEV;
+	}
+
+	ret = cppc_get_perf_caps(cpu, &caps);
+	if (ret)
+		return ret;
+
+	if (ospm_nominal_perf < caps.lowest_perf ||
+	    ospm_nominal_perf > caps.nominal_perf)
+		return -EINVAL;
+
+	return cppc_set_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
+}
+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..6379b7ceee34 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -985,11 +985,50 @@ store_energy_performance_preference_val(struct cpufreq_policy *policy,
 CPPC_CPUFREQ_ATTR_RW_U64(perf_limited, cppc_get_perf_limited,
 			 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;
+	unsigned int freq_khz;
+
+	if (!cpu_data->ospm_nominal_perf)
+		return sysfs_emit(buf, "0\n");
+
+	freq_khz = cppc_perf_to_khz(&cpu_data->perf_caps,
+				    cpu_data->ospm_nominal_perf);
+	return sysfs_emit(buf, "%u\n", freq_khz);
+}
+
+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 sib;
+	u64 freq_khz;
+	u32 perf;
+	int ret;
+
+	ret = kstrtou64(buf, 0, &freq_khz);
+	if (ret)
+		return ret;
+
+	perf = cppc_khz_to_perf(&cpu_data->perf_caps, freq_khz);
+
+	for_each_cpu(sib, policy->cpus) {
+		ret = cppc_set_ospm_nominal_perf(sib, perf);
+		if (ret)
+			return ret;
+	}
+
+	cpu_data->ospm_nominal_perf = perf;
+	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,
@@ -997,6 +1036,7 @@ 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 8693890a7275..0b1dcdbea10a 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -153,6 +153,8 @@ struct cppc_cpudata {
 	struct cppc_perf_fb_ctrs perf_fb_ctrs;
 	unsigned int shared_type;
 	cpumask_var_t shared_cpu_map;
+	/* Cached OSPM Nominal Performance value (write-only register). */
+	u32 ospm_nominal_perf;
 };
 
 #ifdef CONFIG_ACPI_CPPC_LIB
@@ -180,6 +182,7 @@ 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 +269,10 @@ 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