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

[Rafael J. Wysocki (Intel)]

On Tue, Aug 11, 2026 at 2:37 PM Peixin Xie
<peixin.xie at linux.spacemit.com> wrote:
>
> 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 at linux.spacemit.com>
> ---
> 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;
>
> ---

Sashiko has concerns regarding this change:

https://sashiko.dev/#/patchset/20260811-acpi-power-resource-ref-fix-v1-1-828f1c383831%40linux.spacemit.com

Moreover, it is kind of pointless to power up a device and then power
it down almost immediately later.

Have you considered dropping the acpi_bus_init_power() call from
acpi_bus_get_power_flags() and doing it only once when the device gets
ready for enumeration?

Since there should not be any drivers binding directly to struct
acpi_device in the tree now (and struc acpi_device is going to be
dropped entirely in 7.3 if all goes well), something like that should
work.