Hi Enric, On Tue, May 07, 2019 at 11:52:47AM +0200, Enric Balletbo i Serra wrote: > 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 <enric.balle...@collabora.com> > Reviewed-by: Guenter Roeck <gro...@chromium.org> > Acked-by: Adam Thomson <adam.thomson.opensou...@diasemi.com>
Reviewed-by: Benson Leung <ble...@chromium.org> > --- > > Changes in v4: > - Add also input_power_limit. > > Changes in v3: > - Improve commit log and documentation with Benson comments. > > Changes in v2: > - Document the new property in ABI/testing/sysfs-class-power. > - Add the Reviewed-by Guenter Roeck tag. > > 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 5e23e22dce1b..962a27a1daf8 100644 > --- a/Documentation/ABI/testing/sysfs-class-power > +++ b/Documentation/ABI/testing/sysfs-class-power > @@ -331,10 +331,42 @@ 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/<supply_name>/input_voltage_limit > +Date: May 2019 > +Contact: linux...@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/<supply_name>/input_power_limit > +Date: May 2019 > +Contact: linux...@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/<supply_name>/online, > Date: May 2007 > Contact: linux...@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 5358a80d854f..860db617d241 100644 > --- a/drivers/power/supply/power_supply_sysfs.c > +++ b/drivers/power/supply/power_supply_sysfs.c > @@ -275,6 +275,8 @@ static struct device_attribute power_supply_attrs[] = { > POWER_SUPPLY_ATTR(charge_control_limit), > POWER_SUPPLY_ATTR(charge_control_limit_max), > 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 2f9c201a54d1..ba135a5d8996 100644 > --- a/include/linux/power_supply.h > +++ b/include/linux/power_supply.h > @@ -122,6 +122,8 @@ enum power_supply_property { > POWER_SUPPLY_PROP_CHARGE_CONTROL_LIMIT, > POWER_SUPPLY_PROP_CHARGE_CONTROL_LIMIT_MAX, > 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, > -- > 2.20.1 > -- Benson Leung Staff Software Engineer Chrome OS Kernel Google Inc. ble...@google.com Chromium OS Project ble...@chromium.org
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