On 13 December 2018 12:10, Enric Balletbo i Serra wrote: > This is part of 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, ie 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 <[email protected]> > Reviewed-by: Guenter Roeck <[email protected]>
Acked-by: Adam Thomson <[email protected]> > --- > > 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 | 15 +++++++++++++++ > Documentation/power/power_supply_class.txt | 2 ++ > drivers/power/supply/power_supply_sysfs.c | 1 + > include/linux/power_supply.h | 1 + > 4 files changed, 19 insertions(+) > > diff --git a/Documentation/ABI/testing/sysfs-class-power > b/Documentation/ABI/testing/sysfs-class-power > index 5e23e22dce1b..6dee5c105a28 100644 > --- a/Documentation/ABI/testing/sysfs-class-power > +++ b/Documentation/ABI/testing/sysfs-class-power > @@ -335,6 +335,21 @@ Description: > Access: Read, Write > Valid values: Represented in microamps > > +What: > /sys/class/power_supply/<supply_name>/input_voltage_limit > +Date: Nov 2018 > +Contact: [email protected] > +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. > + > + Access: Read, Write > + Valid values: Represented in microvolts > + > What: /sys/class/power_supply/<supply_name>/online, > Date: May 2007 > Contact: [email protected] > diff --git a/Documentation/power/power_supply_class.txt > b/Documentation/power/power_supply_class.txt > index 300d37896e51..7b4be615b4f8 100644 > --- a/Documentation/power/power_supply_class.txt > +++ b/Documentation/power/power_supply_class.txt > @@ -137,6 +137,8 @@ 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. > > 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 dce24f596160..5848742ebb59 100644 > --- a/drivers/power/supply/power_supply_sysfs.c > +++ b/drivers/power/supply/power_supply_sysfs.c > @@ -275,6 +275,7 @@ 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(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 > f80769175c56..608ba88e32ee 100644 > --- a/include/linux/power_supply.h > +++ b/include/linux/power_supply.h > @@ -122,6 +122,7 @@ 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_ENERGY_FULL_DESIGN, > POWER_SUPPLY_PROP_ENERGY_EMPTY_DESIGN, > POWER_SUPPLY_PROP_ENERGY_FULL, > -- > 2.19.2
