[PATCH 2/3] cpufreq: CPPC: Keep the target core awake when reading its cpufreq rate

[Zeng Heng]

As ARM AMU's document says, all counters are subject to any changes
in clock frequency, including clock stopping caused by the WFI and WFE
instructions.

Therefore, using smp_call_on_cpu() to trigger target CPU to
read self's AMU counters, which ensures the counters are working
properly while cstate feature is enabled.

Reported-by: Sumit Gupta <sumitg at nvidia.com>
Link: https://lore.kernel.org/all/20230418113459.12860-7-sumitg@nvidia.com/
Signed-off-by: Zeng Heng <zengheng4 at huawei.com>
---
 drivers/cpufreq/cppc_cpufreq.c | 39 ++++++++++++++++++++++++++--------
 1 file changed, 30 insertions(+), 9 deletions(-)

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index fe08ca419b3d..321a9dc9484d 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -90,6 +90,12 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,
 				 struct cppc_perf_fb_ctrs *fb_ctrs_t0,
 				 struct cppc_perf_fb_ctrs *fb_ctrs_t1);
 
+struct fb_ctr_pair {
+	u32 cpu;
+	struct cppc_perf_fb_ctrs fb_ctrs_t0;
+	struct cppc_perf_fb_ctrs fb_ctrs_t1;
+};
+
 /**
  * cppc_scale_freq_workfn - CPPC arch_freq_scale updater for frequency invariance
  * @work: The work item.
@@ -840,9 +846,24 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,
 	return (reference_perf * delta_delivered) / delta_reference;
 }
 
+static int cppc_get_perf_ctrs_pair(void *val)
+{
+	struct fb_ctr_pair *fb_ctrs = val;
+	int cpu = fb_ctrs->cpu;
+	int ret;
+
+	ret = cppc_get_perf_ctrs(cpu, &fb_ctrs->fb_ctrs_t0);
+	if (ret)
+		return ret;
+
+	udelay(2); /* 2usec delay between sampling */
+
+	return cppc_get_perf_ctrs(cpu, &fb_ctrs->fb_ctrs_t1);
+}
+
 static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
 {
-	struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
+	struct fb_ctr_pair fb_ctrs = { .cpu = cpu, };
 	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
 	struct cppc_cpudata *cpu_data = policy->driver_data;
 	u64 delivered_perf;
@@ -850,18 +871,18 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
 
 	cpufreq_cpu_put(policy);
 
-	ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t0);
-	if (ret)
-		return 0;
-
-	udelay(2); /* 2usec delay between sampling */
+	if (cpu_has_amu_feat(cpu))
+		ret = smp_call_on_cpu(cpu, cppc_get_perf_ctrs_pair,
+				      &fb_ctrs, false);
+	else
+		ret = cppc_get_perf_ctrs_pair(&fb_ctrs);
 
-	ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
 	if (ret)
 		return 0;
 
-	delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0,
-					       &fb_ctrs_t1);
+	delivered_perf = cppc_perf_from_fbctrs(cpu_data,
+					      &fb_ctrs.fb_ctrs_t0,
+					      &fb_ctrs.fb_ctrs_t1);
 
 	return cppc_cpufreq_perf_to_khz(cpu_data, delivered_perf);
 }
-- 
2.25.1