linux-kernel - [PATCH v2 1/2] cpufreq: CPPC: keep target core awake when reading its cpufreq rate

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Date:   Tue, 16 May 2023 21:32:46 +0800
From:   Zeng Heng <zengheng4@...wei.com>
To:     <lenb@...nel.org>, <viresh.kumar@...aro.org>, <rafael@...nel.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
        <wangxiongfeng2@...wei.com>, <xiexiuqi@...wei.com>,
        <liwei391@...wei.com>, <linux-acpi@...r.kernel.org>,
        <weiyongjun1@...wei.com>
Subject: [PATCH v2 1/2] cpufreq: CPPC: keep target core awake when reading its cpufreq rate

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 during calculation.

Signed-off-by: Zeng Heng <zengheng4@...wei.com>
---
 drivers/cpufreq/cppc_cpufreq.c | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 022e3555407c..910167f58bb3 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -837,9 +837,24 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,
 	return (reference_perf * delta_delivered) / delta_reference;
 }
 
+static int cppc_get_perf_ctrs_smp(void *val)
+{
+	int cpu = smp_processor_id();
+	struct cppc_perf_fb_ctrs *fb_ctrs = val;
+	int ret;
+
+	ret = cppc_get_perf_ctrs(cpu, fb_ctrs);
+	if (ret)
+		return ret;
+
+	udelay(2); /* 2usec delay between sampling */
+
+	return 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;
@@ -847,19 +862,12 @@ 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 ret;
-
-	udelay(2); /* 2usec delay between sampling */
-
-	ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
+	ret = smp_call_on_cpu(cpu, cppc_get_perf_ctrs_smp, fb_ctrs, 1);
 	if (ret)
 		return ret;
 
-	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 + 1);
 	return cppc_cpufreq_perf_to_khz(cpu_data, delivered_perf);
 }
 
-- 
2.25.1