[PATCH] ACPI: scan: Drop power resource references for deferred devices

[Peixin Xie]

acpi_bus_get_power_flags() initializes the device power state and takes
references to any power resources required by that state.

If the device is not ready for enumeration, acpi_bus_attach() parks it
and clears power_manageable without dropping those references. When the
dependency is later satisfied, power initialization takes the references
again. The additional references prevent the resources from being
turned off when the device enters D3.

Transition the device to D3cold before clearing power_manageable to drop
the references acquired during initial power state initialization.

This is particularly easy to trigger on RISC-V, where dependencies on
interrupt controllers are derived automatically from interrupt resources.

Signed-off-by: Peixin Xie <peixin.xie@xxxxxxxxxxxxxxxxxx>
---
This issue was reproduced on a SpacemiT K3 RISC-V platform. 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:

  [    0.403217] ACPI: \_SB_.USBD.PDPR: ACPI: PM: Power resource is on
  [    0.409393] ACPI: \_SB_.USBD.PDPR: New power resource
  [    0.419165] ACPI Debug:  "ACPI USBD: entering PDPR._ON"
  [    0.424495] ACPI: \_SB_.USBD.PDPR: ACPI: PM: Power resource turned on
  [    0.431036] ACPI Debug:  "ACPI USBD: entering _PS0"
  [    0.790826] ACPI: \_SB_.USBD.PDPR: ACPI: PM: Power resource already on
  [    0.801777] ACPI Debug:  "ACPI USBD: entering _PS0"
  [    0.995285] ACPI Debug:  "ACPI USBD: entering _PS3"
  [    1.005550] ACPI: \_SB_.USBD.PDPR: ACPI: PM: Power resource still in use

After the change, the reference acquired before deferred enumeration is
dropped, and _OFF is evaluated both when the device is deferred and when
it later enters D3:

  [    0.340111] ACPI Debug:  "ACPI USBD: entering PDPR._ON"
  [    0.345459] ACPI Debug:  "ACPI USBD: entering _PS0"
  [    0.350532] ACPI Debug:  "ACPI USBD: entering PDPR._OFF"
  [    0.742054] ACPI Debug:  "ACPI USBD: entering PDPR._ON"
  [    0.747282] ACPI Debug:  "ACPI USBD: entering _PS0"
  [    0.758664] ACPI Debug:  "ACPI USBD: entering _PS3"
  [    0.768959] ACPI Debug:  "ACPI USBD: entering PDPR._OFF"
---
 drivers/acpi/scan.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index 9a7ac2eb9ce0..7a8404719fa1 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -2350,6 +2350,11 @@ static int acpi_bus_attach(struct acpi_device *device, void *first_pass)
 	acpi_bus_get_status(device);
 	/* Skip devices that are not ready for enumeration (e.g. not present) */
 	if (!acpi_dev_ready_for_enumeration(device)) {
+		/*
+		 * Drop power resource references acquired during initial
+		 * power state initialization before parking the device.
+		 */
+		acpi_power_transition(device, ACPI_STATE_D3_COLD);
 		device->flags.initialized = false;
 		acpi_device_clear_enumerated(device);
 		device->flags.power_manageable = 0;

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

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