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

[Peixin Xie]

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);

---
base-commit: d58772d8520c7ef247c4b95c9bd76d3a25da9ff5
change-id: 20260811-acpi-power-resource-ref-fix-2fa4798f590b

Best regards,
--  
Peixin Xie <peixin.xie@xxxxxxxxxxxxxxxxxx>