From 9a303892acac58e77704d336418fa9ae92e3f70f Mon Sep 17 00:00:00 2001 From: Xueqin Luo Date: Fri, 15 May 2026 10:42:42 +0800 Subject: [PATCH] cpufreq: cppc: mask Desired_Excursion when autonomous selection is enabled According to the ACPI 6.6 specification, the Desired_Excursion field is not utilized when autonomous selection is enabled. In this mode, the bit is architecturally ignored and does not carry meaningful information. Currently, the kernel exposes the raw Performance Limited register value to userspace through the cpufreq sysfs interface. This may lead to misinterpretation, as userspace may assume Desired_Excursion is valid even when autonomous selection is active. To provide a stable and semantically correct ABI, mask out the Desired_Excursion bit when autonomous selection is enabled, so that userspace does not observe undefined or misleading values. Writes are left unchanged, as the field is architecturally ignored in this mode and write attempts are harmless. Signed-off-by: Xueqin Luo Reviewed-by: Pierre Gondois Reviewed-by: Sumit Gupta Signed-off-by: Viresh Kumar --- drivers/cpufreq/cppc_cpufreq.c | 29 ++++++++++++++++++++++++++++- 1 file changed, 28 insertions(+), 1 deletion(-) diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c index 7e7f9dfb7a24..bf5175f7551c 100644 --- a/drivers/cpufreq/cppc_cpufreq.c +++ b/drivers/cpufreq/cppc_cpufreq.c @@ -982,7 +982,34 @@ store_energy_performance_preference_val(struct cpufreq_policy *policy, return count; } -CPPC_CPUFREQ_ATTR_RW_U64(perf_limited, cppc_get_perf_limited, +static int cppc_get_perf_limited_filtered(int cpu, u64 *perf_limited) +{ + struct cpufreq_policy *policy; + struct cppc_cpudata *cpu_data; + int ret; + + ret = cppc_get_perf_limited(cpu, perf_limited); + if (ret) + return ret; + + policy = cpufreq_cpu_get_raw(cpu); + if (!policy) + return -EINVAL; + + cpu_data = policy->driver_data; + + /* + * Desired Excursion is ignored when autonomous selection is + * enabled. Clear the bit to avoid exposing meaningless state + * to userspace. + */ + if (cpu_data && cpu_data->perf_ctrls.auto_sel) + *perf_limited &= ~CPPC_PERF_LIMITED_DESIRED_EXCURSION; + + return 0; +} + +CPPC_CPUFREQ_ATTR_RW_U64(perf_limited, cppc_get_perf_limited_filtered, cppc_set_perf_limited) cpufreq_freq_attr_ro(freqdomain_cpus);