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Diffstat (limited to '')
| -rw-r--r-- | Documentation/thermal/power_allocator.rst (renamed from Documentation/thermal/power_allocator.txt) | 144 |
1 files changed, 84 insertions, 60 deletions
diff --git a/Documentation/thermal/power_allocator.txt b/Documentation/thermal/power_allocator.rst index 9fb0ff06dca9..67b6a3297238 100644 --- a/Documentation/thermal/power_allocator.txt +++ b/Documentation/thermal/power_allocator.rst @@ -1,3 +1,4 @@ +================================= Power allocator governor tunables ================================= @@ -25,36 +26,36 @@ temperature as the control input and power as the controlled output: P_max = k_p * e + k_i * err_integral + k_d * diff_err + sustainable_power where - e = desired_temperature - current_temperature - err_integral is the sum of previous errors - diff_err = e - previous_error - -It is similar to the one depicted below: - - k_d - | -current_temp | - | v - | +----------+ +---+ - | +----->| diff_err |-->| X |------+ - | | +----------+ +---+ | - | | | tdp actor - | | k_i | | get_requested_power() - | | | | | | | - | | | | | | | ... - v | v v v v v - +---+ | +-------+ +---+ +---+ +---+ +----------+ - | S |-------+----->| sum e |----->| X |--->| S |-->| S |-->|power | - +---+ | +-------+ +---+ +---+ +---+ |allocation| - ^ | ^ +----------+ - | | | | | - | | +---+ | | | - | +------->| X |-------------------+ v v - | +---+ granted performance -desired_temperature ^ - | - | - k_po/k_pu + - e = desired_temperature - current_temperature + - err_integral is the sum of previous errors + - diff_err = e - previous_error + +It is similar to the one depicted below:: + + k_d + | + current_temp | + | v + | +----------+ +---+ + | +----->| diff_err |-->| X |------+ + | | +----------+ +---+ | + | | | tdp actor + | | k_i | | get_requested_power() + | | | | | | | + | | | | | | | ... + v | v v v v v + +---+ | +-------+ +---+ +---+ +---+ +----------+ + | S |-----+----->| sum e |----->| X |--->| S |-->| S |-->|power | + +---+ | +-------+ +---+ +---+ +---+ |allocation| + ^ | ^ +----------+ + | | | | | + | | +---+ | | | + | +------->| X |-------------------+ v v + | +---+ granted performance + desired_temperature ^ + | + | + k_po/k_pu Sustainable power ----------------- @@ -73,7 +74,7 @@ is typically 2000mW, while on a 10" tablet is around 4500mW (may vary depending on screen size). If you are using device tree, do add it as a property of the -thermal-zone. For example: +thermal-zone. For example:: thermal-zones { soc_thermal { @@ -85,7 +86,7 @@ thermal-zone. For example: Instead, if the thermal zone is registered from the platform code, pass a `thermal_zone_params` that has a `sustainable_power`. If no `thermal_zone_params` were being passed, then something like below -will suffice: +will suffice:: static const struct thermal_zone_params tz_params = { .sustainable_power = 3500, @@ -112,18 +113,18 @@ available capacity at a low temperature. On the other hand, a high value of `k_pu` will result in the governor granting very high power while temperature is low, and may lead to temperature overshooting. -The default value for `k_pu` is: +The default value for `k_pu` is:: 2 * sustainable_power / (desired_temperature - switch_on_temp) This means that at `switch_on_temp` the output of the controller's proportional term will be 2 * `sustainable_power`. The default value -for `k_po` is: +for `k_po` is:: sustainable_power / (desired_temperature - switch_on_temp) Focusing on the proportional and feed forward values of the PID -controller equation we have: +controller equation we have:: P_max = k_p * e + sustainable_power @@ -134,21 +135,23 @@ is the desired one, then the proportional component is zero and thermal equilibrium under constant load. `sustainable_power` is only an estimate, which is the reason for closed-loop control such as this. -Expanding `k_pu` we get: +Expanding `k_pu` we get:: + P_max = 2 * sustainable_power * (T_set - T) / (T_set - T_on) + - sustainable_power + sustainable_power -where - T_set is the desired temperature - T is the current temperature - T_on is the switch on temperature +where: + + - T_set is the desired temperature + - T is the current temperature + - T_on is the switch on temperature When the current temperature is the switch_on temperature, the above -formula becomes: +formula becomes:: P_max = 2 * sustainable_power * (T_set - T_on) / (T_set - T_on) + - sustainable_power = 2 * sustainable_power + sustainable_power = - 3 * sustainable_power + sustainable_power = 2 * sustainable_power + sustainable_power = + 3 * sustainable_power Therefore, the proportional term alone linearly decreases power from 3 * `sustainable_power` to `sustainable_power` as the temperature @@ -178,11 +181,18 @@ Cooling device power API Cooling devices controlled by this governor must supply the additional "power" API in their `cooling_device_ops`. It consists on three ops: -1. int get_requested_power(struct thermal_cooling_device *cdev, - struct thermal_zone_device *tz, u32 *power); -@cdev: The `struct thermal_cooling_device` pointer -@tz: thermal zone in which we are currently operating -@power: pointer in which to store the calculated power +1. :: + + int get_requested_power(struct thermal_cooling_device *cdev, + struct thermal_zone_device *tz, u32 *power); + + +@cdev: + The `struct thermal_cooling_device` pointer +@tz: + thermal zone in which we are currently operating +@power: + pointer in which to store the calculated power `get_requested_power()` calculates the power requested by the device in milliwatts and stores it in @power . It should return 0 on @@ -190,23 +200,37 @@ success, -E* on failure. This is currently used by the power allocator governor to calculate how much power to give to each cooling device. -2. int state2power(struct thermal_cooling_device *cdev, struct - thermal_zone_device *tz, unsigned long state, u32 *power); -@cdev: The `struct thermal_cooling_device` pointer -@tz: thermal zone in which we are currently operating -@state: A cooling device state -@power: pointer in which to store the equivalent power +2. :: + + int state2power(struct thermal_cooling_device *cdev, struct + thermal_zone_device *tz, unsigned long state, + u32 *power); + +@cdev: + The `struct thermal_cooling_device` pointer +@tz: + thermal zone in which we are currently operating +@state: + A cooling device state +@power: + pointer in which to store the equivalent power Convert cooling device state @state into power consumption in milliwatts and store it in @power. It should return 0 on success, -E* on failure. This is currently used by thermal core to calculate the maximum power that an actor can consume. -3. int power2state(struct thermal_cooling_device *cdev, u32 power, - unsigned long *state); -@cdev: The `struct thermal_cooling_device` pointer -@power: power in milliwatts -@state: pointer in which to store the resulting state +3. :: + + int power2state(struct thermal_cooling_device *cdev, u32 power, + unsigned long *state); + +@cdev: + The `struct thermal_cooling_device` pointer +@power: + power in milliwatts +@state: + pointer in which to store the resulting state Calculate a cooling device state that would make the device consume at most @power mW and store it in @state. It should return 0 on success, |