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From:   George Cherian <george.cherian@cavium.com>
To:     linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Cc:     viresh.kumar@linaro.org, rjw@rjwysocki.net,
        pprakash@codeaurora.org, George Cherian <george.cherian@cavium.com>
Subject: [PATCH v2] cpufreq / CPPC: Add cpuinfo_cur_freq support for CPPC
Date:   Fri, 15 Jun 2018 03:03:15 -0700
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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@cavium.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
---
 drivers/cpufreq/cppc_cpufreq.c | 71 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)

diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 3464580..3fe7625 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -296,10 +296,81 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
 	return ret;
 }
 
+static int cppc_get_rate_from_fbctrs(struct cppc_cpudata *cpu,
+				     struct cppc_perf_fb_ctrs fb_ctrs_t0,
+				     struct cppc_perf_fb_ctrs fb_ctrs_t1)
+{
+	u64 delta_reference, delta_delivered;
+	u64 reference_perf, delivered_perf;
+
+	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
+		 * We also need to find whether the low level fw
+		 * maintains 32 bit or 64 bit counters, to calculate
+		 * the correct delta.
+		 */
+		if (fb_ctrs_t0.reference > (~(u32)0))
+			delta_reference  = (~((u64)0) - fb_ctrs_t0.reference) +
+					fb_ctrs_t1.reference;
+		else
+			delta_reference  = (~((u32)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
+		 * We also need to find whether the low level fw
+		 * maintains 32 bit or 64 bit counters, to calculate
+		 * the correct delta.
+		 */
+		if (fb_ctrs_t0.delivered > (~(u32)0))
+			delta_delivered  = (~((u64)0) - fb_ctrs_t0.delivered) +
+					fb_ctrs_t1.delivered;
+		else
+			delta_delivered  = (~((u32)0) - fb_ctrs_t0.delivered) +
+					fb_ctrs_t1.delivered;
+	}
+
+	if (delta_reference)  /* Check to avoid divide-by zero */
+		delivered_perf = (reference_perf * delta_delivered) /
+					delta_reference;
+	else
+		delivered_perf = reference_perf;
+
+	return cppc_cpufreq_perf_to_khz(cpu, delivered_perf);
+}
+
+static unsigned int cppc_cpufreq_get_rate(unsigned int cpunum)
+{
+	struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
+	struct cppc_cpudata *cpu = all_cpu_data[cpunum];
+	int ret;
+
+	ret = cppc_get_perf_ctrs(cpunum, &fb_ctrs_t0);
+	if (ret)
+		return ret;
+
+	udelay(2); /* 2usec delay between sampling */
+
+	ret = cppc_get_perf_ctrs(cpunum, &fb_ctrs_t1);
+	if (ret)
+		return ret;
+
+	return cppc_get_rate_from_fbctrs(cpu, 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",
-- 
2.7.4