Re: [REGRESSION] - Multiple userspace implementations of battery estimate broken after "ACPI: battery: negate current when discharging"

[Hans de Goede <hansg@kernel.org>]

Hi Matthew,

On 3-Jul-25 3:54 AM, Matthew Schwartz wrote:
> Hello,
> 
> I installed kernel 6.15.4 to find that my battery estimate on my handheld gaming device was completely inaccurate, instead giving negative values and an unknown estimated battery life in multiple places. 
> 
> After bisecting, I landed on "ACPI: battery: negate current when discharging” as the bad commit. This commit breaks not one but several userspace implementations of battery monitoring: Steam and MangoHud. Perhaps it breaks more, but those are the two I have noticed so far. 

Thank you for reporting this.

As Rafael already indicated this patch will need to be reverted to
unbreak userspace.

But, the patch was actually doing the right thing, according to:

Documentation/ABI/testing/sysfs-class-power

What:           /sys/class/power_supply/<supply_name>/current_avg
Date:           May 2007
Contact:        linux-pm@vger.kernel.org
Description:
                Battery:
...
                Access: Read

                Valid values: Represented in microamps. Negative values are
                used for discharging batteries, positive values for charging
                batteries and for USB IBUS current.

(and the same for current_now)

and there are many power_supply fuel-gauge drivers (1) under
drivers/power/supply/ which do adhere to this specification
and report a negative current for discharging.

So if any of the userspace consumers of this API you mention
were to run on hw with these drivers the same problem will
be hit. Can you please file bugs against these userspace
projects so that they can fix this?

Regards,

Hans



1) For directly accessing fuel-gauge chips on devices where these
are directly accessible instead of being exposed through ACPI