@@ -274,7 +274,7 @@ described below.
Usage: optional
Value type: <prop-encoded-array>
Definition: A u32 value that represents the running time dynamic
- power coefficient in units of mW/MHz/uV^2. The
+ power coefficient in units of uW/MHz/V^2. The
coefficient can either be calculated from power
measurements or derived by analysis.
@@ -285,7 +285,7 @@ described below.
Pdyn = dynamic-power-coefficient * V^2 * f
- where voltage is in uV, frequency is in MHz.
+ where voltage is in V, frequency is in MHz.
Example 1 (dual-cluster big.LITTLE system 32-bit):
The unit of dynamic-power-coefficient is described as mW/MHz/uV^2 whereas its usage in the code assumes that unit is uW/MHz/V^2 In drivers/thermal/cpu_cooling.c, the code is : power = (u64)capacitance * freq_mhz * voltage_mv * voltage_mv; do_div(power, 1000000000); which can be summarized as : power (mW) = capacitance * freq_mhz/1000 * (voltage_mv/1000)^2 or power (mW) = (capacitance * freq_mhz * (voltage_mv/1000)^2) / 1000 then power (mW) = power (uW) / 1000 so power (uW) = capacitance * freq_mhz * (voltage_mv/1000)^2 Furthermore, if we test basic values like : voltage_mv = 1000mV = 1V freq_mhz = 1000Mhz The minimum possible power, when dynamic-power-coefficient equals 1, will be with current unit: min power = 1 * 1000 * (1000000)^2 = 10^15 mW which is not realistic With the unit used by the code, the min power is min power = 1 * 1000 * 1^2 = 1000uW = 1mW which is far more realistic Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> --- Documentation/devicetree/bindings/arm/cpus.txt | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) -- 2.7.4