PM: EM: convert power field to micro-Watts precision and align drivers

The milli-Watts precision causes rounding errors while calculating
efficiency cost for each OPP. This is especially visible in the 'simple'
Energy Model (EM), where the power for each OPP is provided from OPP
framework. This can cause some OPPs to be marked inefficient, while
using micro-Watts precision that might not happen.

Update all EM users which access 'power' field and assume the value is
in milli-Watts.

Solve also an issue with potential overflow in calculation of energy
estimation on 32bit machine. It's needed now since the power value
(thus the 'cost' as well) are higher.

Example calculation which shows the rounding error and impact:

power = 'dyn-power-coeff' * volt_mV * volt_mV * freq_MHz

power_a_uW = (100 * 600mW * 600mW * 500MHz) / 10^6 = 18000
power_a_mW = (100 * 600mW * 600mW * 500MHz) / 10^9 = 18

power_b_uW = (100 * 605mW * 605mW * 600MHz) / 10^6 = 21961
power_b_mW = (100 * 605mW * 605mW * 600MHz) / 10^9 = 21

max_freq = 2000MHz

cost_a_mW = 18 * 2000MHz/500MHz = 72
cost_a_uW = 18000 * 2000MHz/500MHz = 72000

cost_b_mW = 21 * 2000MHz/600MHz = 70 // <- artificially better
cost_b_uW = 21961 * 2000MHz/600MHz = 73203

The 'cost_b_mW' (which is based on old milli-Watts) is misleadingly
better that the 'cost_b_uW' (this patch uses micro-Watts) and such
would have impact on the 'inefficient OPPs' information in the Cpufreq
framework. This patch set removes the rounding issue.

Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c
index 6d2a4cf46db7..bfd35583d653 100644
--- a/drivers/cpufreq/scmi-cpufreq.c
+++ b/drivers/cpufreq/scmi-cpufreq.c
@@ -19,6 +19,7 @@
 #include <linux/slab.h>
 #include <linux/scmi_protocol.h>
 #include <linux/types.h>
+#include <linux/units.h>
 
 struct scmi_data {
 	int domain_id;
@@ -99,6 +100,7 @@ static int __maybe_unused
 scmi_get_cpu_power(struct device *cpu_dev, unsigned long *power,
 		   unsigned long *KHz)
 {
+	bool power_scale_mw = perf_ops->power_scale_mw_get(ph);
 	unsigned long Hz;
 	int ret, domain;
 
@@ -112,6 +114,10 @@ scmi_get_cpu_power(struct device *cpu_dev, unsigned long *power,
 	if (ret)
 		return ret;
 
+	/* Provide bigger resolution power to the Energy Model */
+	if (power_scale_mw)
+		*power *= MICROWATT_PER_MILLIWATT;
+
 	/* The EM framework specifies the frequency in KHz. */
 	*KHz = Hz / 1000;