[PATCH 1/2] cpufreq: CPPC: keep 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_function_single() to trigger target CPU to
read self's AMU counters, which ensures the counters are working
properly during calculation.

Signed-off-by: Zeng Heng <zengheng4@xxxxxxxxxx>
---
 drivers/cpufreq/cppc_cpufreq.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 022e3555407c..169af7ff9a2a 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -837,29 +837,31 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,
 	return (reference_perf * delta_delivered) / delta_reference;
 }
 
+static void cppc_get_perf_ctrs_smp(void *val)
+{
+	int cpu = smp_processor_id();
+	struct cppc_perf_fb_ctrs *fb_ctrs = val;
+
+	cppc_get_perf_ctrs(cpu, fb_ctrs);
+
+	udelay(2); /* 2usec delay between sampling */
+
+	cppc_get_perf_ctrs(cpu, fb_ctrs + 1);
+}
+
 static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
 {
-	struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
+	struct cppc_perf_fb_ctrs fb_ctrs[2] = {0};
 	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
 	struct cppc_cpudata *cpu_data = policy->driver_data;
 	u64 delivered_perf;
-	int ret;
 
 	cpufreq_cpu_put(policy);
 
-	ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t0);
-	if (ret)
-		return ret;
-
-	udelay(2); /* 2usec delay between sampling */
-
-	ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
-	if (ret)
-		return ret;
-
-	delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0,
-					       &fb_ctrs_t1);
+	smp_call_function_single(cpu, cppc_get_perf_ctrs_smp, fb_ctrs, 1);
 
+	delivered_perf = cppc_perf_from_fbctrs(cpu_data, fb_ctrs,
+					       fb_ctrs + 1);
 	return cppc_cpufreq_perf_to_khz(cpu_data, delivered_perf);
 }
 
-- 
2.25.1