linux-kernel - [PATCH] cpufreq / CPPC: Add cpuinfo_cur

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Message-Id: <1526989324-4183-1-git-send-email-george.cherian@cavium.com>
Date:   Tue, 22 May 2018 04:42:04 -0700
From:   George Cherian <george.cherian@...ium.com>
To:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Cc:     rjw@...ysocki.net, viresh.kumar@...aro.org,
        George Cherian <george.cherian@...ium.com>
Subject: [PATCH] cpufreq / CPPC: Add cpuinfo_cur_freq support for CPPC

Per Section 8.4.7.1.3 of ACPI 6.2, The platform provides performance
feedback via set of performance counters. To determine the actual
performance level delivered over time, OSPM may read a set of
performance counters from the Reference Performance Counter Register
and the Delivered Performance Counter Register.

OSPM calculates the delivered performance over a given time period by
taking a beginning and ending snapshot of both the reference and
delivered performance counters, and calculating:

delivered_perf = reference_perf X (delta of delivered_perf counter / delta of reference_perf counter).

Implement the above and hook this to the cpufreq->get method.

Signed-off-by: George Cherian <george.cherian@...ium.com>
---
 drivers/cpufreq/cppc_cpufreq.c | 44 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index b15115a..a046915 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -240,10 +240,54 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
 	return ret;
 }
 
+static int cppc_get_rate_from_fbctrs(struct cppc_perf_fb_ctrs fb_ctrs_t0,
+				     struct cppc_perf_fb_ctrs fb_ctrs_t1)
+{
+	u64 delta_reference, delta_delivered;
+	u64 reference_perf, ratio;
+
+	reference_perf = fb_ctrs_t0.reference_perf;
+	if (fb_ctrs_t1.reference > fb_ctrs_t0.reference)
+		delta_reference = fb_ctrs_t1.reference - fb_ctrs_t0.reference;
+	else /* Counters would have wrapped-around */
+		delta_reference  = ((u64)(~((u64)0)) - fb_ctrs_t0.reference) +
+					fb_ctrs_t1.reference;
+
+	if (fb_ctrs_t1.delivered > fb_ctrs_t0.delivered)
+		delta_delivered = fb_ctrs_t1.delivered - fb_ctrs_t0.delivered;
+	else /* Counters would have wrapped-around */
+		delta_delivered  = ((u64)(~((u64)0)) - fb_ctrs_t0.delivered) +
+					fb_ctrs_t1.delivered;
+
+	if (delta_reference)  /* Check to avoid divide-by zero */
+		ratio = (delta_delivered * 1000) / delta_reference;
+	else
+		return -EINVAL;
+
+	return (reference_perf * ratio) / 1000;
+}
+
+static unsigned int cppc_cpufreq_get_rate(unsigned int cpunum)
+{
+	struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
+	int ret;
+
+	ret = cppc_get_perf_ctrs(cpunum, &fb_ctrs_t0);
+	if (ret)
+		return ret;
+
+	ret = cppc_get_perf_ctrs(cpunum, &fb_ctrs_t1);
+	if (ret)
+		return ret;
+
+	return cppc_get_rate_from_fbctrs(fb_ctrs_t0, fb_ctrs_t1);
+}
+
 static struct cpufreq_driver cppc_cpufreq_driver = {
 	.flags = CPUFREQ_CONST_LOOPS,
 	.verify = cppc_verify_policy,
 	.target = cppc_cpufreq_set_target,
+	.get = cppc_cpufreq_get_rate,
 	.init = cppc_cpufreq_cpu_init,
 	.stop_cpu = cppc_cpufreq_stop_cpu,
 	.name = "cppc_cpufreq",
-- 
1.8.3.1