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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Fri, 5 Jun 2020 13:30:13 +0200
Message-ID: <CAJZ5v0iteOV=4CnQrVx5ZmnWq5Uf88k7UMMmKcMxgJnco3kxvg@mail.gmail.com>
Subject: Re: [PATCH] acpi: battery: Always read fresh battery state on update
To:     Mathew King <mathewk@chromium.org>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Len Brown <lenb@kernel.org>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>
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On Thu, Jun 4, 2020 at 9:57 PM Mathew King <mathewk@chromium.org> wrote:
>
> When the ACPI battery receives a notification event it should always
> read the battery state fresh from the ACPI device and not use the cached
> state.

Why should it?

> Currently the cached state stays valid and the new state may not
> be read when a notification occurs. This can lead to a udev event
> showing that the battery has changed but the sysfs state will still have
> the cached state values.

Is there a bug entry or similar related to that which can be referred
to from this patch?

> This change invalidates the update time forcing
> the state to be updated before notifying the power_supply subsystem of
> the change.
>
> Signed-off-by: Mathew King <mathewk@chromium.org>
> ---
>  drivers/acpi/battery.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
> index 366c389175d8..ab7fa4879fbe 100644
> --- a/drivers/acpi/battery.c
> +++ b/drivers/acpi/battery.c
> @@ -981,6 +981,7 @@ static int acpi_battery_update(struct acpi_battery *battery, bool resume)
>                 acpi_battery_init_alarm(battery);
>         }
>
> +       battery->update_time = 0;

AFAICS this is equivalent to dropping battery->update_time altogether.
Isn't that a bit too excessive?

>         result = acpi_battery_get_state(battery);
>         if (result)
>                 return result;
> --