driver-api/thermal/power_allocator.rst

6 -----------
20 --------------
23 Proportional-Integral-Derivative controller (PID controller) with
29    -  e = desired_temperature - current_temperature
30    -  err_integral is the sum of previous errors
31    -  diff_err = e - previous_error
39        |              +----------+   +---+
40        |       +----->| diff_err |-->| X |------+
41        |       |      +----------+   +---+      |
47      +---+     |      +-------+      +---+    +---+   +---+   +----------+
48      | S |-----+----->| sum e |----->| X |--->| S |-->| S |-->|power     |
49      +---+     |      +-------+      +---+    +---+   +---+   |allocation|
50        ^       |                                ^             +----------+
52        |       |        +---+                   |                |     |
53        |       +------->| X |-------------------+                v     v
54        |                +---+                               granted performance
61 -----------------
70 to the speed-grade of the silicon.  `sustainable_power` is therefore
79 thermal-zone.  For example::
81 	thermal-zones {
83 			polling-delay = <1000>;
84 			polling-delay-passive = <100>;
85 			sustainable-power = <2500>;
101 -------------
104 thermal governor allows the configuration of two proportional term
105 constants: `k_po` and `k_pu`.  `k_po` is the proportional term
108 proportional term constant during temperature undershoot periods
120     2 * sustainable_power / (desired_temperature - switch_on_temp)
123 proportional term will be 2 * `sustainable_power`.  The default value
126     sustainable_power / (desired_temperature - switch_on_temp)
133 The proportional term is proportional to the difference between the
138 an estimate, which is the reason for closed-loop control such as this.
142     P_max = 2 * sustainable_power * (T_set - T) / (T_set - T_on) +
147     - T_set is the desired temperature
148     - T is the current temperature
149     - T_on is the switch on temperature
154     P_max = 2 * sustainable_power * (T_set - T_on) / (T_set - T_on) +
158 Therefore, the proportional term alone linearly decreases power from
163 -----------------------
165 `k_i` configures the PID loop's integral term constant.  This term
166 allows the PID controller to compensate for long term drift and for
170 integral term.  This term is then multiplied by `k_i` and the result
175 ---
177 `k_d` configures the PID loop's derivative term constant.  It's
201 success, -E* on failure.  This is currently used by the power
208 			thermal_zone_device *tz, unsigned long state,
221 milliwatts and store it in @power.  It should return 0 on success, -E*
228 			unsigned long *state);
239 -E* on failure.  This is currently used by the thermal core to convert
246 ----------------------
261 as the `contribution` property of each map in the `cooling-maps` node.
271 governor, step-wise will also misbehave if you call its throttle()
280 thermal zone should have power values reported either in milli-Watts