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, 16 insertions, 8 deletions

diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
index 6c373f2960e7..f82111837b8d 100644
--- a/kernel/power/energy_model.c
+++ b/kernel/power/energy_model.c
@@ -145,7 +145,7 @@ static int em_create_perf_table(struct device *dev, struct em_perf_domain *pd,
 
 		/*
 		 * The power returned by active_state() is expected to be
-		 * positive and to fit into 16 bits.
+		 * positive and be in range.
 		 */
 		if (!power || power > EM_MAX_POWER) {
 			dev_err(dev, "EM: invalid power: %lu\n",
@@ -170,7 +170,7 @@ static int em_create_perf_table(struct device *dev, struct em_perf_domain *pd,
 				goto free_ps_table;
 			}
 		} else {
-			power_res = em_scale_power(table[i].power);
+			power_res = table[i].power;
 			cost = div64_u64(fmax * power_res, table[i].frequency);
 		}
 
@@ -201,9 +201,17 @@ static int em_create_pd(struct device *dev, int nr_states,
 {
 	struct em_perf_domain *pd;
 	struct device *cpu_dev;
-	int cpu, ret;
+	int cpu, ret, num_cpus;
 
 	if (_is_cpu_device(dev)) {
+		num_cpus = cpumask_weight(cpus);
+
+		/* Prevent max possible energy calculation to not overflow */
+		if (num_cpus > EM_MAX_NUM_CPUS) {
+			dev_err(dev, "EM: too many CPUs, overflow possible\n");
+			return -EINVAL;
+		}
+
 		pd = kzalloc(sizeof(*pd) + cpumask_size(), GFP_KERNEL);
 		if (!pd)
 			return -ENOMEM;
@@ -314,13 +322,13 @@ EXPORT_SYMBOL_GPL(em_cpu_get);
  * @cpus	: Pointer to cpumask_t, which in case of a CPU device is
  *		obligatory. It can be taken from i.e. 'policy->cpus'. For other
  *		type of devices this should be set to NULL.
- * @milliwatts	: Flag indicating that the power values are in milliWatts or
+ * @microwatts	: Flag indicating that the power values are in micro-Watts or
  *		in some other scale. It must be set properly.
  *
  * Create Energy Model tables for a performance domain using the callbacks
  * defined in cb.
  *
- * The @milliwatts is important to set with correct value. Some kernel
+ * The @microwatts is important to set with correct value. Some kernel
  * sub-systems might rely on this flag and check if all devices in the EM are
  * using the same scale.
  *
@@ -331,7 +339,7 @@ EXPORT_SYMBOL_GPL(em_cpu_get);
  */
 int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
 				struct em_data_callback *cb, cpumask_t *cpus,
-				bool milliwatts)
+				bool microwatts)
 {
 	unsigned long cap, prev_cap = 0;
 	unsigned long flags = 0;
@@ -381,8 +389,8 @@ int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
 		}
 	}
 
-	if (milliwatts)
-		flags |= EM_PERF_DOMAIN_MILLIWATTS;
+	if (microwatts)
+		flags |= EM_PERF_DOMAIN_MICROWATTS;
 	else if (cb->get_cost)
 		flags |= EM_PERF_DOMAIN_ARTIFICIAL;