Re: [PATCH v3 2/2] acpi: battery: Read Battery charge time for Steamdeck devices

[Rafael J. Wysocki (Intel)]

On Wed, Oct 14, 2026 at 10:44 PM Umang Jain <uajain@xxxxxxxxxx> wrote:
>
> Valve steamdeck devices can report battery status as
> charging, even when low-powered power supply is connected
> to the device. The battery status is reported as charging
> through sysfs, even though in reality, it is discharging.
>
> To handle this case, read out Battery charge time ("_BCT")
> as it is reported accurately on these devices, hence use that
> information for report charging vs discharging status.
> Battery charge time ("_BCT") with an eligible power supply unit
> will have valid values whereas with a low-powered supply unit,
> it shall report ACPI_BATTERY_VALUE_UNKNOWN. Use this as a
> differentiator to determine, whether the battery of steamdeck
> devices is really charging or not.
>
> Signed-off-by: Umang Jain <uajain@xxxxxxxxxx>

I think that it would be better to merge this patch with the [1/2].

> ---
>  drivers/acpi/battery.c | 25 ++++++++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
> index fa20900bea0e..b7818695b6cb 100644
> --- a/drivers/acpi/battery.c
> +++ b/drivers/acpi/battery.c
> @@ -242,7 +242,7 @@ static int acpi_battery_get_property(struct power_supply *psy,
>                                         : POWER_SUPPLY_STATUS_DISCHARGING;
>                                 return 0;
>                         }
> -               else if (battery->state & ACPI_BATTERY_STATE_CHARGING)
> +               else if (battery->state & ACPI_BATTERY_STATE_CHARGING) {
>                         /* Check the rate and capacity to validate the status. */
>                         if (!acpi_battery_is_full(battery) ||
>                             (battery->rate_now != ACPI_BATTERY_VALUE_UNKNOWN &&
> @@ -252,6 +252,29 @@ static int acpi_battery_get_property(struct power_supply *psy,
>                                 /* Full and zero rate. */
>                                 val->intval = POWER_SUPPLY_STATUS_NOT_CHARGING;
>                         }
> +
> +                       /*
> +                        * For Valve Steamdeck devices, evaluate _BCT to determine
> +                        * if we are really charging.
> +                        */
> +                       if (test_bit(ACPI_BATTERY_QUIRK_VALVE_STEAMDECK, &battery->flags) &&
> +                           acpi_has_method(battery->device->handle, "_BCT")) {

Can you check the _BCT presence at the time when the quirk bit is set
and avoid setting the bit when _BCT is not present?  That would allow
you to just test the bit here.

> +                               unsigned long long bct;
> +                               acpi_status status;
> +                               union acpi_object arg0 = { ACPI_TYPE_INTEGER };
> +                               struct acpi_object_list args = { 1, &arg0 };
> +
> +                               arg0.integer.value = 100;
> +                               status = acpi_evaluate_integer(battery->device->handle, "_BCT",
> +                                                              &args, &bct);
> +                               if (ACPI_FAILURE(status) || bct > ACPI_UINT32_MAX)
> +                                       acpi_handle_info(battery->device->handle,

This should be acpi_handle_debug(), but I'm not sure if this message
is interesting at all, especially if _BCT fails every time.  Also, it
may be confusing in the bct > ACPI_UINT32_MAX case because it may
print "success" then.

> +                                                        "_BCT evaluation failed: %s",
> +                                                        acpi_format_exception(status));
> +                               else if (bct == ACPI_BATTERY_VALUE_UNKNOWN)
> +                                       val->intval = POWER_SUPPLY_STATUS_DISCHARGING;
> +                       }
> +               }
>                 else if (battery->state & ACPI_BATTERY_STATE_CHARGE_LIMITING)
>                         val->intval = POWER_SUPPLY_STATUS_NOT_CHARGING;
>                 else if (acpi_battery_is_charged(battery))
> --