linux-kernel - Re: [PATCH RESEND] power: supply: qcom_battmgr: abs() on POWER

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Message-ID: <ioiy4ixlvx5gxl3f4pqshwxz35ktrqghju2circpnd3qicgemc@oohazfsfvuag>
Date: Fri, 14 Feb 2025 02:36:17 +0100
From: aruhier@...lbox.org
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Sebastian Reichel <sre@...nel.org>, linux-arm-msm@...r.kernel.org, 
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND] power: supply: qcom_battmgr: abs() on POWER_NOW
 property

On Fri, Feb 14, 2025 at 12:24:18AM +0200, Dmitry Baryshkov wrote:
> On Thu, Feb 13, 2025 at 05:51:38PM +0100, Anthony Ruhier via B4 Relay wrote:
> > From: Anthony Ruhier <aruhier@...lbox.org>
> >
> > The value for the POWER_NOW property is by default negative when the
> > battery is discharging, positive when charging.
> >
> > However on x1e laptops it breaks several userland tools that give a
> > prediction of the battery run time (such as the acpi command, powertop
> > or the waybar battery module), as these tools do not expect a negative
> > value for /sys/class/power_supply/qcom-battmgr-bat/power_now. They
> > estimate the battery run time by dividing the value of energy_full by
> > power_now. The battery percentage is calculated by dividing energy_full
> > by energy_now, therefore it is not impacted.
> >
> > While having a negative number during discharge makes sense, it is not
> > standard with how other battery drivers expose it. Instead, it seems
> > standard to have a positive value for power_now, and rely on the status
> > file instead to know if the battery is charging or discharging. It is
> > what other x86 laptops do.
>
> Documentation/ABI does not define ABI for the power_now. However for
> current_now it clearly defines that it can be positive or negative.
>
> >
> > Without the patch:
> >     $ acpi
> >     Battery 0: Discharging, 98%, discharging at zero rate - will never fully discharge.
> >
> > With the patch:
> >     $ acpi
> >     Battery 0: Discharging, 97%, 10:18:27 remaining
> >
> > ---
> > Signed-off-by: Anthony Ruhier <aruhier@...lbox.org>
> > ---
> >  drivers/power/supply/qcom_battmgr.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
>
> --
> With best wishes
> Dmitry

I see. But as it breaks existing tools when power_now is negative, should we
change the behavior of these tools or adapt the driver?

As it does not seem common that power_now and current_now are negative in
other drivers, tools using these values rely on the status anyway. I'm
wondering if it provides anything to keep this behavior.

--
Regards,
Anthony Ruhier