ACPI: CPPC: Move reference performance to capabilities

Currently, the `Reference Performance` register is read every time
the CPU frequency is sampled in `cppc_get_perf_ctrs()`. This function
is on the hot path of the cppc_cpufreq driver.

Reference Performance indicates the performance level that corresponds
to the Reference Counter incrementing and is not expected to change
dynamically during runtime (unlike the Delivered and Reference counters).

Reading this register in the hot path incurs unnecessary overhead,
particularly on platforms where CPC registers are located in the PCC
(Platform Communication Channel) subspace. This patch moves
`reference_perf` from the dynamic feedback counters structure
(`cppc_perf_fb_ctrs`) to the static capabilities structure
(`cppc_perf_caps`).

Signed-off-by: Pengjie Zhang <zhangpengjie2@huawei.com>
[ rjw: Changelog adjustment ]
Link: https://patch.msgid.link/20260213100935.19111-1-zhangpengjie2@huawei.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 12 insertions, 9 deletions

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 94d489a4c90d..5dfb109cf1f4 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -50,7 +50,8 @@ struct cppc_freq_invariance {
 static DEFINE_PER_CPU(struct cppc_freq_invariance, cppc_freq_inv);
 static struct kthread_worker *kworker_fie;
 
-static int cppc_perf_from_fbctrs(struct cppc_perf_fb_ctrs *fb_ctrs_t0,
+static int cppc_perf_from_fbctrs(u64 reference_perf,
+				 struct cppc_perf_fb_ctrs *fb_ctrs_t0,
 				 struct cppc_perf_fb_ctrs *fb_ctrs_t1);
 
 /**
@@ -70,7 +71,7 @@ static void __cppc_scale_freq_tick(struct cppc_freq_invariance *cppc_fi)
 	struct cppc_perf_fb_ctrs fb_ctrs = {0};
 	struct cppc_cpudata *cpu_data;
 	unsigned long local_freq_scale;
-	u64 perf;
+	u64 perf, ref_perf;
 
 	cpu_data = cppc_fi->cpu_data;
 
@@ -79,7 +80,9 @@ static void __cppc_scale_freq_tick(struct cppc_freq_invariance *cppc_fi)
 		return;
 	}
 
-	perf = cppc_perf_from_fbctrs(&cppc_fi->prev_perf_fb_ctrs, &fb_ctrs);
+	ref_perf = cpu_data->perf_caps.reference_perf;
+	perf = cppc_perf_from_fbctrs(ref_perf,
+				     &cppc_fi->prev_perf_fb_ctrs, &fb_ctrs);
 	if (!perf)
 		return;
 
@@ -747,13 +750,11 @@ static inline u64 get_delta(u64 t1, u64 t0)
 	return (u32)t1 - (u32)t0;
 }
 
-static int cppc_perf_from_fbctrs(struct cppc_perf_fb_ctrs *fb_ctrs_t0,
+static int cppc_perf_from_fbctrs(u64 reference_perf,
+				 struct cppc_perf_fb_ctrs *fb_ctrs_t0,
 				 struct cppc_perf_fb_ctrs *fb_ctrs_t1)
 {
 	u64 delta_reference, delta_delivered;
-	u64 reference_perf;
-
-	reference_perf = fb_ctrs_t0->reference_perf;
 
 	delta_reference = get_delta(fb_ctrs_t1->reference,
 				    fb_ctrs_t0->reference);
@@ -790,7 +791,7 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
 	struct cpufreq_policy *policy __free(put_cpufreq_policy) = cpufreq_cpu_get(cpu);
 	struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
 	struct cppc_cpudata *cpu_data;
-	u64 delivered_perf;
+	u64 delivered_perf, reference_perf;
 	int ret;
 
 	if (!policy)
@@ -807,7 +808,9 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
 			return 0;
 	}
 
-	delivered_perf = cppc_perf_from_fbctrs(&fb_ctrs_t0, &fb_ctrs_t1);
+	reference_perf = cpu_data->perf_caps.reference_perf;
+	delivered_perf = cppc_perf_from_fbctrs(reference_perf,
+					       &fb_ctrs_t0, &fb_ctrs_t1);
 	if (!delivered_perf)
 		goto out_invalid_counters;