From a4496d52b3430cb3c4c16d03cdd5f4ee97ad1241 Mon Sep 17 00:00:00 2001 From: Enric Balletbo i Serra Date: Tue, 7 May 2019 11:52:47 +0200 Subject: [PATCH] power: supply: add input power and voltage limit properties For thermal management strategy you might be interested on limit the input power for a power supply. We already have current limit but basically what we probably want is to limit power. So, introduce the input_power_limit property. Although the common use case is limit the input power, in some specific cases it is the voltage that is problematic (i.e some regulators have different efficiencies at higher voltage resulting in more heat). So introduce also the input_voltage_limit property. This happens in one Chromebook and is used on the Pixel C's thermal management strategy to effectively limit the input power to 5V 3A when the screen is on. When the screen is on, the display, the CPU, and the GPU all contribute more heat to the system than while the screen is off, and we made a tradeoff to throttle the charger in order to give more of the thermal budget to those other components. So there's nothing fundamentally broken about the hardware that would cause the Pixel C to malfunction if we were charging at 9V or 12V instead of 5V when the screen is on, i.e. if userspace doesn't change this. What would happen is that you wouldn't meet Google's skin temperature targets on the system if the charger was allowed to run at 9V or 12V with the screen on. For folks hacking on Pixel Cs (which is now outside of Google's official support window for Android) and customizing their own kernel and userspace this would be acceptable, but we wanted to expose this feature in the power supply properties because the feature does exist in the Emedded Controller firmware of the Pixel C and all of Google's Chromebooks with USB-C made since 2015 in case someone running an up to date kernel wanted to limit the charging power for thermal or other reasons. This patch exposes a new property, similar to input current limit, to re-configure the maximum voltage from the external supply at runtime based on system-level knowledge or user input. Signed-off-by: Enric Balletbo i Serra Reviewed-by: Guenter Roeck Acked-by: Adam Thomson Reviewed-by: Benson Leung Signed-off-by: Sebastian Reichel --- Documentation/ABI/testing/sysfs-class-power | 32 +++++++++++++++++++++ Documentation/power/power_supply_class.txt | 4 +++ drivers/power/supply/power_supply_sysfs.c | 2 ++ include/linux/power_supply.h | 2 ++ 4 files changed, 40 insertions(+) diff --git a/Documentation/ABI/testing/sysfs-class-power b/Documentation/ABI/testing/sysfs-class-power index b77e30b9014e..27edc06e2495 100644 --- a/Documentation/ABI/testing/sysfs-class-power +++ b/Documentation/ABI/testing/sysfs-class-power @@ -376,10 +376,42 @@ Description: supply. Normally this is configured based on the type of connection made (e.g. A configured SDP should output a maximum of 500mA so the input current limit is set to the same value). + Use preferably input_power_limit, and for problems that can be + solved using power limit use input_current_limit. Access: Read, Write Valid values: Represented in microamps +What: /sys/class/power_supply//input_voltage_limit +Date: May 2019 +Contact: linux-pm@vger.kernel.org +Description: + This entry configures the incoming VBUS voltage limit currently + set in the supply. Normally this is configured based on + system-level knowledge or user input (e.g. This is part of the + Pixel C's thermal management strategy to effectively limit the + input power to 5V when the screen is on to meet Google's skin + temperature targets). Note that this feature should not be + used for safety critical things. + Use preferably input_power_limit, and for problems that can be + solved using power limit use input_voltage_limit. + + Access: Read, Write + Valid values: Represented in microvolts + +What: /sys/class/power_supply//input_power_limit +Date: May 2019 +Contact: linux-pm@vger.kernel.org +Description: + This entry configures the incoming power limit currently set + in the supply. Normally this is configured based on + system-level knowledge or user input. Use preferably this + feature to limit the incoming power and use current/voltage + limit only for problems that can be solved using power limit. + + Access: Read, Write + Valid values: Represented in microwatts + What: /sys/class/power_supply//online, Date: May 2007 Contact: linux-pm@vger.kernel.org diff --git a/Documentation/power/power_supply_class.txt b/Documentation/power/power_supply_class.txt index 300d37896e51..1e3c705111db 100644 --- a/Documentation/power/power_supply_class.txt +++ b/Documentation/power/power_supply_class.txt @@ -137,6 +137,10 @@ power supply object. INPUT_CURRENT_LIMIT - input current limit programmed by charger. Indicates the current drawn from a charging source. +INPUT_VOLTAGE_LIMIT - input voltage limit programmed by charger. Indicates +the voltage limit from a charging source. +INPUT_POWER_LIMIT - input power limit programmed by charger. Indicates +the power limit from a charging source. CHARGE_CONTROL_LIMIT - current charge control limit setting CHARGE_CONTROL_LIMIT_MAX - maximum charge control limit setting diff --git a/drivers/power/supply/power_supply_sysfs.c b/drivers/power/supply/power_supply_sysfs.c index a704a76d7529..829e12c800e5 100644 --- a/drivers/power/supply/power_supply_sysfs.c +++ b/drivers/power/supply/power_supply_sysfs.c @@ -277,6 +277,8 @@ static struct device_attribute power_supply_attrs[] = { POWER_SUPPLY_ATTR(charge_control_start_threshold), POWER_SUPPLY_ATTR(charge_control_end_threshold), POWER_SUPPLY_ATTR(input_current_limit), + POWER_SUPPLY_ATTR(input_voltage_limit), + POWER_SUPPLY_ATTR(input_power_limit), POWER_SUPPLY_ATTR(energy_full_design), POWER_SUPPLY_ATTR(energy_empty_design), POWER_SUPPLY_ATTR(energy_full), diff --git a/include/linux/power_supply.h b/include/linux/power_supply.h index d5b15e039f4f..cbb708b57b11 100644 --- a/include/linux/power_supply.h +++ b/include/linux/power_supply.h @@ -129,6 +129,8 @@ enum power_supply_property { POWER_SUPPLY_PROP_CHARGE_CONTROL_START_THRESHOLD, /* in percents! */ POWER_SUPPLY_PROP_CHARGE_CONTROL_END_THRESHOLD, /* in percents! */ POWER_SUPPLY_PROP_INPUT_CURRENT_LIMIT, + POWER_SUPPLY_PROP_INPUT_VOLTAGE_LIMIT, + POWER_SUPPLY_PROP_INPUT_POWER_LIMIT, POWER_SUPPLY_PROP_ENERGY_FULL_DESIGN, POWER_SUPPLY_PROP_ENERGY_EMPTY_DESIGN, POWER_SUPPLY_PROP_ENERGY_FULL,