From 13c45a26635fa51a68911aa57e6778bdad18b103 Mon Sep 17 00:00:00 2001 From: Sumit Gupta Date: Fri, 6 Feb 2026 19:56:57 +0530 Subject: ACPI: CPPC: add APIs and sysfs interface for perf_limited 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. It contains two sticky bits set by the platform: - Bit 0 (Desired_Excursion): Set when delivered performance is constrained below desired performance. Not used when Autonomous Selection is enabled. - Bit 1 (Minimum_Excursion): Set when delivered performance is constrained below minimum performance. These bits remain set until OSPM explicitly clears them. The write operation accepts a bitmask of bits to clear: - Write 0x1 to clear bit 0 - Write 0x2 to clear bit 1 - Write 0x3 to clear both bits This enables users to detect if platform throttling impacted a workload. Users clear the register before execution, run the workload, then check afterward - if set, hardware throttling occurred during that time window. The interface is exposed as: /sys/devices/system/cpu/cpuX/cpufreq/perf_limited Signed-off-by: Sumit Gupta Reviewed-by: Pierre Gondois Reviewed-by: Lifeng Zheng Link: https://patch.msgid.link/20260206142658.72583-7-sumitg@nvidia.com Signed-off-by: Rafael J. Wysocki --- include/acpi/cppc_acpi.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'include/acpi') diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h index 3fc796c0d902..f7afa20b8ad9 100644 --- a/include/acpi/cppc_acpi.h +++ b/include/acpi/cppc_acpi.h @@ -42,6 +42,11 @@ #define CPPC_EPP_PERFORMANCE_PREF 0x00 #define CPPC_EPP_ENERGY_EFFICIENCY_PREF 0xFF +#define CPPC_PERF_LIMITED_DESIRED_EXCURSION BIT(0) +#define CPPC_PERF_LIMITED_MINIMUM_EXCURSION BIT(1) +#define CPPC_PERF_LIMITED_MASK (CPPC_PERF_LIMITED_DESIRED_EXCURSION | \ + CPPC_PERF_LIMITED_MINIMUM_EXCURSION) + /* Each register has the folowing format. */ struct cpc_reg { u8 descriptor; @@ -174,6 +179,8 @@ extern int cppc_get_auto_act_window(int cpu, u64 *auto_act_window); extern int cppc_set_auto_act_window(int cpu, u64 auto_act_window); extern int cppc_get_auto_sel(int cpu, bool *enable); extern int cppc_set_auto_sel(int cpu, bool enable); +extern int cppc_get_perf_limited(int cpu, u64 *perf_limited); +extern int cppc_set_perf_limited(int cpu, u64 bits_to_clear); extern int amd_get_highest_perf(unsigned int cpu, u32 *highest_perf); extern int amd_get_boost_ratio_numerator(unsigned int cpu, u64 *numerator); extern int amd_detect_prefcore(bool *detected); @@ -270,6 +277,14 @@ static inline int cppc_set_auto_sel(int cpu, bool enable) { 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 bits_to_clear) +{ + return -EOPNOTSUPP; +} static inline int amd_get_highest_perf(unsigned int cpu, u32 *highest_perf) { return -ENODEV; -- cgit v1.2.3