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, 8 insertions, 7 deletions

diff --git a/drivers/opp/of.c b/drivers/opp/of.c
index 30394929d700..eb89c9a75985 100644
--- a/drivers/opp/of.c
+++ b/drivers/opp/of.c
@@ -1443,12 +1443,12 @@ EXPORT_SYMBOL_GPL(dev_pm_opp_get_of_node);
  * It provides the power used by @dev at @kHz if it is the frequency of an
  * existing OPP, or at the frequency of the first OPP above @kHz otherwise
  * (see dev_pm_opp_find_freq_ceil()). This function updates @kHz to the ceiled
- * frequency and @mW to the associated power.
+ * frequency and @uW to the associated power.
  *
  * Returns 0 on success or a proper -EINVAL value in case of error.
  */
 static int __maybe_unused
-_get_dt_power(struct device *dev, unsigned long *mW, unsigned long *kHz)
+_get_dt_power(struct device *dev, unsigned long *uW, unsigned long *kHz)
 {
 	struct dev_pm_opp *opp;
 	unsigned long opp_freq, opp_power;
@@ -1465,7 +1465,7 @@ _get_dt_power(struct device *dev, unsigned long *mW, unsigned long *kHz)
 		return -EINVAL;
 
 	*kHz = opp_freq / 1000;
-	*mW = opp_power / 1000;
+	*uW = opp_power;
 
 	return 0;
 }
@@ -1475,14 +1475,14 @@ _get_dt_power(struct device *dev, unsigned long *mW, unsigned long *kHz)
  * This computes the power estimated by @dev at @kHz if it is the frequency
  * of an existing OPP, or at the frequency of the first OPP above @kHz otherwise
  * (see dev_pm_opp_find_freq_ceil()). This function updates @kHz to the ceiled
- * frequency and @mW to the associated power. The power is estimated as
+ * frequency and @uW to the associated power. The power is estimated as
  * P = C * V^2 * f with C being the device's capacitance and V and f
  * respectively the voltage and frequency of the OPP.
  *
  * Returns -EINVAL if the power calculation failed because of missing
  * parameters, 0 otherwise.
  */
-static int __maybe_unused _get_power(struct device *dev, unsigned long *mW,
+static int __maybe_unused _get_power(struct device *dev, unsigned long *uW,
 				     unsigned long *kHz)
 {
 	struct dev_pm_opp *opp;
@@ -1512,9 +1512,10 @@ static int __maybe_unused _get_power(struct device *dev, unsigned long *mW,
 		return -EINVAL;
 
 	tmp = (u64)cap * mV * mV * (Hz / 1000000);
-	do_div(tmp, 1000000000);
+	/* Provide power in micro-Watts */
+	do_div(tmp, 1000000);
 
-	*mW = (unsigned long)tmp;
+	*uW = (unsigned long)tmp;
 	*kHz = Hz / 1000;
 
 	return 0;