Re: [PATCH v2] ACPI: scan: Defer device power initialization

[Rafael J. Wysocki (Intel)]

On Thu, Aug 20, 2026 at 7:56 AM Peixin Xie
<peixin.xie@xxxxxxxxxxxxxxxxxx> wrote:
>
> acpi_bus_get_power_flags() initializes the device power state while the
> ACPI device object is being created, before checking whether the device
> is ready for enumeration.
>
> If enumeration is deferred, acpi_bus_attach() clears the initialized and
> power_manageable flags. When the dependency is later satisfied,
> acpi_bus_init_power() is called again and takes additional references to
> the power resources used by the device. These references prevent the
> resources from being turned off when the device enters D3.
>
> Remove the early acpi_bus_init_power() call and leave regular ACPI device
> objects uninitialized until acpi_bus_attach() runs after the device is
> ready for enumeration.
>
> Power resource objects are initialized through acpi_add_power_resource()
> and do not require the generic initialization in acpi_bus_attach(), so
> mark them as initialized there.
>
> This also avoids powering up devices before their dependencies are
> available.
>
> Signed-off-by: Peixin Xie <peixin.xie@xxxxxxxxxxxxxxxxxx>
> ---
> This issue was reproduced on a SpacemiT K3 RISC-V Pico-ITX. The affected
> device uses a power resource through _PR0 and has an automatically derived
> dependency on its interrupt controller.
>
> Before the change, the initial power initialization acquires a power
> resource reference. The device is then deferred, but that reference is not
> dropped. When the dependency becomes available, power initialization
> acquires another reference. Consequently, entering D3 only drops the
> reference count from 2 to 1 and _OFF is not evaluated:
>
>  [    0.314611] ACPI Debug:  "I2P2 _STA"
>  [    0.318260] ACPI: \_SB_.I2P2: ACPI: PM: Power resource is on
>  [    0.323998] ACPI: \_SB_.I2P2: New power resource
>  [    0.382108] ACPI Debug:  "I2P2 _STA"
>  [    0.478964] ACPI Debug:  "I2P2 _ON"
>  [    0.482498] ACPI: \_SB_.I2P2: ACPI: PM: Power resource turned on
>  [    0.488597] ACPI Debug:  "I2C2, PS0"
>  [    0.863170] ACPI: \_SB_.I2P2: ACPI: PM: Power resource already on
>  [    0.873686] ACPI Debug:  "I2C2, PS0"
>  [    2.416055] ACPI Debug:  "I2C2, PS3"
>  [    2.423397] ACPI: \_SB_.I2P2: ACPI: PM: Power resource still in use
>
> After the change, device power state initialization is deferred until its
> dependency is met. Since no reference is acquired before then, the power
> resource left on by firmware is turned off as unused after the namespace
> scan. Once the dependency is met, the resource is turned on once for the
> device and is turned off normally when the device later enters D3:
>
> [    0.314628] ACPI Debug:  "I2P2 _STA"
>  [    0.318277] ACPI: \_SB_.I2P2: ACPI: PM: Power resource is on
>  [    0.324016] ACPI: \_SB_.I2P2: New power resource
>  [    0.382118] ACPI Debug:  "I2P2 _STA"
>  [    0.496116] ACPI: \_SB_.I2P2: ACPI: PM: Turning OFF
>  [    0.501081] ACPI Debug:  "I2P2 _OFF"
>  [    0.504705] ACPI: \_SB_.I2P2: ACPI: PM: Power resource turned off
>  [    1.415899] ACPI Debug:  "I2P2 _ON"
>  [    1.418866] ACPI: \_SB_.I2P2: ACPI: PM: Power resource turned on
>  [    1.424947] ACPI Debug:  "I2C2, PS0"
>  [    2.647655] ACPI Debug:  "I2C2, PS3"
>  [    2.654856] ACPI Debug:  "I2P2 _OFF"
>  [    2.654866] ACPI: \_SB_.I2P2: ACPI: PM: Power resource turned off
> ---
> Changes in v2:
> - Replace the D3cold transition added in v1 with deferred device power
>   initialization, as suggested by Rafael.
> - Mark power resource objects as initialized in their dedicated creation
>   path.
> - Link to v1: https://patch.msgid.link/20260811-acpi-power-resource-ref-fix-v1-1-828f1c383831@xxxxxxxxxxxxxxxxxx
> ---
>  drivers/acpi/power.c | 1 +
>  drivers/acpi/scan.c  | 4 ----
>  2 files changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/drivers/acpi/power.c b/drivers/acpi/power.c
> index d4131c184be8..4f1479103bfe 100644
> --- a/drivers/acpi/power.c
> +++ b/drivers/acpi/power.c
> @@ -955,6 +955,7 @@ struct acpi_device *acpi_add_power_resource(acpi_handle handle)
>         INIT_LIST_HEAD(&resource->dependents);
>         device->power.state = ACPI_STATE_UNKNOWN;
>         device->flags.match_driver = true;
> +       device->flags.initialized = true;
>
>         /* Evaluate the object to get the system level and resource order. */
>         status = acpi_evaluate_object(handle, NULL, NULL, &buffer);
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index 9a7ac2eb9ce0..489352ba80e1 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -1141,9 +1141,6 @@ static void acpi_bus_get_power_flags(struct acpi_device *device)
>                 if (!list_empty(&device->power.states[ACPI_STATE_D3_HOT].resources))
>                         device->power.states[ACPI_STATE_D3_COLD].flags.valid = 1;
>         }
> -
> -       if (acpi_bus_init_power(device))
> -               device->flags.power_manageable = 0;
>  }
>
>  static void acpi_bus_get_flags(struct acpi_device *device)
> @@ -1822,7 +1819,6 @@ void acpi_init_device_object(struct acpi_device *device, acpi_handle handle,
>         acpi_init_properties(device);
>         acpi_bus_get_flags(device);
>         device->flags.match_driver = false;
> -       device->flags.initialized = true;
>         device->flags.enumeration_by_parent =
>                 acpi_device_enumeration_by_parent(device);
>         acpi_device_clear_enumerated(device);
>
> ---

Applied as 7.3-rc material, thanks!