On 12/05/2023 18:48, Pavel Machek wrote:
Hi!
I've been working on a driver for the charger found in most Snapdragon
845 phones (the OnePlus 6, SHIFT6mq, PocoPhone F1, etc). I wanted to
include support for the POWER_SUPPLY_PROP_CHARGE_CONTROL_LIMIT
property.
My understanding is that it exposes the current limit as a cooling
device so that userspace (or frameworks like DTPM) can optimise for
performance in a thermally constrained device by limiting the input
current and thus reducing the heat generated by the charger circuitry,
a similar idea was applied on the Pixel C:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a4496d52b3430cb3c4c16d03cdd5f4ee97ad1241
However, reading through the sysfs docs for cooling devices, and
looking at the implementation in power_supply_core.c, it seems like the
behavior here is wrong in a few ways:
1. The values should scale from 0: no cooling to max_state: max
cooling, but the power_supply docs and the only existing implementation
(the smbb driver) just export the current_limit, such that increasing
cur_state would increase the current limit, not decrease it.
2. (unsure?)The scale is completely different to most other cooling
devices, most cooling devices don't seem to have a max state much
beyond the double digits, but CHARGE_CONTROL_LIMIT is on the scale of
uA, so approaches like incrementing the cooling state by 1 don't really
work.
Did this get solved somehow?
Thanks for resurrecting the discussion.
Anyway, I am not sure mW will be useful here, as elsewhere it is mW
thermal and here it is mW from charger. Most of that energy should be
stored in battery, not converted to heat.
I'm not sure to understand the comment. The question is about decreasing
the speed of the charge of the battery because the faster it charges the
warmer it gets. Doing a fast charge is ok, if the phone is for instance
on a table doing nothing. But if the environment is hot (a car, a
pocket) or there are other sources of heat on the phone like a game, the
temperature of the battery could be too high (or the skin temperature).
In this case we have to balance the heat contribution of the different
components by reducing their performances. The first knob to act on is
to reduce the charge speed of the battery by reducing the delivered power.
For that we need a connection between the thermal framework which
monitors the battery temperature and the power supply to reduce the
charge speed when it is too hot. This connection is the cooling device.
The cooling devices have opaque values where the min and max cooling
effect vary depending on the implementation (eg. a fan 0/1, a LCD light
0/1023).
Here the power supply has yet another unit (uA) to act on and difficult
to translate to a cooling device discrete numbers (that is my
understanding).
My suggestion is adding to the power supply the power capping capability
using the powercap framework and add it to the DTPM nomenclature.
With enough components in DTPM, it will be possible to create a generic
power cooling device using the unified unit uW with the powercap API.
--
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog
