linux-kernel - [PATCH v3 5/8] ACPI: CPPC: add APIs and sysfs interface for perf

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Message-ID: <20251001150104.1275188-6-sumitg@nvidia.com>
Date: Wed, 1 Oct 2025 20:31:01 +0530
From: Sumit Gupta <sumitg@...dia.com>
To: <rafael@...nel.org>, <viresh.kumar@...aro.org>, <lenb@...nel.org>,
	<robert.moore@...el.com>, <corbet@....net>, <pierre.gondois@....com>,
	<zhenglifeng1@...wei.com>, <rdunlap@...radead.org>, <ray.huang@....com>,
	<gautham.shenoy@....com>, <mario.limonciello@....com>, <perry.yuan@....com>,
	<linux-pm@...r.kernel.org>, <linux-acpi@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <acpica-devel@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>
CC: <linux-tegra@...r.kernel.org>, <treding@...dia.com>,
	<jonathanh@...dia.com>, <vsethi@...dia.com>, <ksitaraman@...dia.com>,
	<sanjayc@...dia.com>, <bbasu@...dia.com>, <sumitg@...dia.com>
Subject: [PATCH v3 5/8] ACPI: CPPC: add APIs and sysfs interface for perf_limited register

Add sysfs interface to read/write the Performance Limited register.

The Performance Limited register indicates to the OS that an
unpredictable event (like thermal throttling) has limited processor
performance. This register is sticky and remains set until reset or
OS clears it by writing 0.

The interface is exposed as:
 /sys/devices/system/cpu/cpuX/cpufreq/perf_limited

Signed-off-by: Sumit Gupta <sumitg@...dia.com>
---
 drivers/acpi/cppc_acpi.c       | 26 ++++++++++++++++++++++++++
 drivers/cpufreq/cppc_cpufreq.c | 12 ++++++++++++
 include/acpi/cppc_acpi.h       | 10 ++++++++++
 3 files changed, 48 insertions(+)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index d47aec2aed13..ce99c3f3ae85 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1806,6 +1806,32 @@ int cppc_set_max_perf(int cpu, u64 max_perf)
 }
 EXPORT_SYMBOL_GPL(cppc_set_max_perf);
 
+/**
+ * cppc_get_perf_limited - Get the Performance Limited register value.
+ * @cpu: CPU from which to get Performance Limited register.
+ * @perf_limited: Pointer to store the Performance Limited value.
+ *
+ * Return: 0 for success, -EIO on register access failure, -EOPNOTSUPP if not supported.
+ */
+int cppc_get_perf_limited(int cpu, u64 *perf_limited)
+{
+	return cppc_get_reg_val(cpu, PERF_LIMITED, perf_limited);
+}
+EXPORT_SYMBOL_GPL(cppc_get_perf_limited);
+
+/**
+ * cppc_set_perf_limited() - Write the Performance Limited register.
+ * @cpu: CPU on which to write register.
+ * @perf_limited: Value to write to the perf_limited register.
+ *
+ * Return: 0 for success, -EIO on register access failure, -EOPNOTSUPP if not supported.
+ */
+int cppc_set_perf_limited(int cpu, u64 perf_limited)
+{
+	return cppc_set_reg_val(cpu, PERF_LIMITED, perf_limited);
+}
+EXPORT_SYMBOL_GPL(cppc_set_perf_limited);
+
 /**
  * cppc_get_perf - Get a CPU's performance controls.
  * @cpu: CPU for which to get performance controls.
diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 864978674efc..9946adfeeee4 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -984,12 +984,23 @@ static ssize_t store_max_perf(struct cpufreq_policy *policy, const char *buf, si
 	return count;
 }
 
+static ssize_t show_perf_limited(struct cpufreq_policy *policy, char *buf)
+{
+	return cppc_cpufreq_sysfs_show_u64(policy->cpu, cppc_get_perf_limited, buf);
+}
+
+static ssize_t store_perf_limited(struct cpufreq_policy *policy, const char *buf, size_t count)
+{
+	return cppc_cpufreq_sysfs_store_u64(buf, count, cppc_set_perf_limited, policy->cpu);
+}
+
 cpufreq_freq_attr_ro(freqdomain_cpus);
 cpufreq_freq_attr_rw(auto_select);
 cpufreq_freq_attr_rw(auto_act_window);
 cpufreq_freq_attr_rw(energy_performance_preference_val);
 cpufreq_freq_attr_rw(min_perf);
 cpufreq_freq_attr_rw(max_perf);
+cpufreq_freq_attr_rw(perf_limited);
 
 static struct freq_attr *cppc_cpufreq_attr[] = {
 	&freqdomain_cpus,
@@ -998,6 +1009,7 @@ static struct freq_attr *cppc_cpufreq_attr[] = {
 	&energy_performance_preference_val,
 	&min_perf,
 	&max_perf,
+	&perf_limited,
 	NULL,
 };
 
diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index fc7614eb9dcb..9fc28fb1890b 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -177,6 +177,8 @@ extern int cppc_get_min_perf(int cpu, u64 *min_perf);
 extern int cppc_set_min_perf(int cpu, u64 min_perf);
 extern int cppc_get_max_perf(int cpu, u64 *max_perf);
 extern int cppc_set_max_perf(int cpu, u64 max_perf);
+extern int cppc_get_perf_limited(int cpu, u64 *perf_limited);
+extern int cppc_set_perf_limited(int cpu, u64 perf_limited);
 extern int amd_get_highest_perf(unsigned int cpu, u32 *highest_perf);
 extern int amd_get_boost_ratio_numerator(unsigned int cpu, u64 *numerator);
 extern int amd_detect_prefcore(bool *detected);
@@ -285,6 +287,14 @@ static inline int cppc_set_max_perf(int cpu, u64 max_perf)
 {
 	return -EOPNOTSUPP;
 }
+static inline int cppc_get_perf_limited(int cpu, u64 *perf_limited)
+{
+	return -EOPNOTSUPP;
+}
+static inline int cppc_set_perf_limited(int cpu, u64 perf_limited)
+{
+	return -EOPNOTSUPP;
+}
 static inline int amd_get_highest_perf(unsigned int cpu, u32 *highest_perf)
 {
 	return -ENODEV;
-- 
2.34.1