linux-kernel - Re: [PATCH] HID: input: do not report stylus battery state as "full"

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Message-ID: <CAO-hwJJ-VyKBohETJabxmgjZ8RtmZHWWOBr2kZNC=feOxHgTtQ@mail.gmail.com>
Date:   Wed, 30 Jun 2021 09:09:27 +0200
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Bastien Nocera <hadess@...ess.net>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Kenneth Albanowski <kenalba@...gle.com>,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] HID: input: do not report stylus battery state as "full"

Hi Dmitry,

On Tue, Jun 29, 2021 at 8:26 PM Dmitry Torokhov
<dmitry.torokhov@...il.com> wrote:
>
> The power supply states of discharging, charging, full, etc, represent
> state of charging, not the capacity level of the battery (for which
> we have a separate property). Current HID usage tables to not allow
> for expressing charging state of the batteries found in generic
> styli, so we should simply assume that the battery is discharging
> even if current capacity is at 100% when battery strength reporting
> is done via HID interface. In fact, we were doing just that before
> commit 581c4484769e.

This commit is 4 year old already, so I'd like to have the opinion of
Bastien on the matter for the upower side (or at least notify him).

>
> This change helps UIs to not mis-represent fully charged batteries in
> styli as being charging/topping-off.
>
> Fixes: 581c4484769e ("HID: input: map digitizer battery usage")
> Reported-by: Kenneth Albanowski <kenalba@...gle.com>
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> ---
>  drivers/hid/hid-input.c | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
> index e982d8173c9c..e85a1a34ff39 100644
> --- a/drivers/hid/hid-input.c
> +++ b/drivers/hid/hid-input.c
> @@ -417,8 +417,6 @@ static int hidinput_get_battery_property(struct power_supply *psy,
>
>                 if (dev->battery_status == HID_BATTERY_UNKNOWN)
>                         val->intval = POWER_SUPPLY_STATUS_UNKNOWN;

What's the point of keeping the HID_BATTERY_UNKNOWN code path? AFAICT,
before 581c4484769e, we were just returning
POWER_SUPPLY_STATUS_DISCHARGING. If we don't need to check for the
capacity, I think we could also drop the hunk just before where we do
the query of the capacity.

Cheers,
Benjamin


> -               else if (dev->battery_capacity == 100)
> -                       val->intval = POWER_SUPPLY_STATUS_FULL;
>                 else
>                         val->intval = POWER_SUPPLY_STATUS_DISCHARGING;
>                 break;
> --
> 2.32.0.93.g670b81a890-goog
>
> --
> Dmitry
>