cpu_cooling: Remove static-power related documentation
commit 84fe2cab4859 ("cpu_cooling: Drop static-power related stuff")
removed support for static-power in kernel, but it missed reflecting the
same in documentation. Remove the static power related documentation
bits as well.
Reported-by: Javi Merino <javi.merino@kernel.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/Documentation/thermal/cpu-cooling-api.txt b/Documentation/thermal/cpu-cooling-api.txt
index 7a1c89d..7df567e 100644
--- a/Documentation/thermal/cpu-cooling-api.txt
+++ b/Documentation/thermal/cpu-cooling-api.txt
@@ -44,16 +44,14 @@
2. Power models
The power API registration functions provide a simple power model for
-CPUs. The current power is calculated as dynamic + (optionally)
-static power. This power model requires that the operating-points of
+CPUs. The current power is calculated as dynamic power (static power isn't
+supported currently). This power model requires that the operating-points of
the CPUs are registered using the kernel's opp library and the
`cpufreq_frequency_table` is assigned to the `struct device` of the
cpu. If you are using CONFIG_CPUFREQ_DT then the
`cpufreq_frequency_table` should already be assigned to the cpu
device.
-2.1 Dynamic power
-
The dynamic power consumption of a processor depends on many factors.
For a given processor implementation the primary factors are:
@@ -92,79 +90,3 @@
from 100 to 500. For reference, the approximate values for the SoC in
ARM's Juno Development Platform are 530 for the Cortex-A57 cluster and
140 for the Cortex-A53 cluster.
-
-
-2.2 Static power
-
-Static leakage power consumption depends on a number of factors. For a
-given circuit implementation the primary factors are:
-
-- Time the circuit spends in each 'power state'
-- Temperature
-- Operating voltage
-- Process grade
-
-The time the circuit spends in each 'power state' for a given
-evaluation period at first order means OFF or ON. However,
-'retention' states can also be supported that reduce power during
-inactive periods without loss of context.
-
-Note: The visibility of state entries to the OS can vary, according to
-platform specifics, and this can then impact the accuracy of a model
-based on OS state information alone. It might be possible in some
-cases to extract more accurate information from system resources.
-
-The temperature, operating voltage and process 'grade' (slow to fast)
-of the circuit are all significant factors in static leakage power
-consumption. All of these have complex relationships to static power.
-
-Circuit implementation specific factors include the chosen silicon
-process as well as the type, number and size of transistors in both
-the logic gates and any RAM elements included.
-
-The static power consumption modelling must take into account the
-power managed regions that are implemented. Taking the example of an
-ARM processor cluster, the modelling would take into account whether
-each CPU can be powered OFF separately or if only a single power
-region is implemented for the complete cluster.
-
-In one view, there are others, a static power consumption model can
-then start from a set of reference values for each power managed
-region (e.g. CPU, Cluster/L2) in each state (e.g. ON, OFF) at an
-arbitrary process grade, voltage and temperature point. These values
-are then scaled for all of the following: the time in each state, the
-process grade, the current temperature and the operating voltage.
-However, since both implementation specific and complex relationships
-dominate the estimate, the appropriate interface to the model from the
-cpu cooling device is to provide a function callback that calculates
-the static power in this platform. When registering the cpu cooling
-device pass a function pointer that follows the `get_static_t`
-prototype:
-
- int plat_get_static(cpumask_t *cpumask, int interval,
- unsigned long voltage, u32 &power);
-
-`cpumask` is the cpumask of the cpus involved in the calculation.
-`voltage` is the voltage at which they are operating. The function
-should calculate the average static power for the last `interval`
-milliseconds. It returns 0 on success, -E* on error. If it
-succeeds, it should store the static power in `power`. Reading the
-temperature of the cpus described by `cpumask` is left for
-plat_get_static() to do as the platform knows best which thermal
-sensor is closest to the cpu.
-
-If `plat_static_func` is NULL, static power is considered to be
-negligible for this platform and only dynamic power is considered.
-
-The platform specific callback can then use any combination of tables
-and/or equations to permute the estimated value. Process grade
-information is not passed to the model since access to such data, from
-on-chip measurement capability or manufacture time data, is platform
-specific.
-
-Note: the significance of static power for CPUs in comparison to
-dynamic power is highly dependent on implementation. Given the
-potential complexity in implementation, the importance and accuracy of
-its inclusion when using cpu cooling devices should be assessed on a
-case by case basis.
-