ACPI Advanced Seed

Power Resource in ACPI

How ACPI PowerResource objects model shared rails and why wrong _ON/_OFF ordering can break Wi-Fi, camera, Bluetooth, and resume behavior.

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A device does not always own its power rail alone.

A camera, Wi-Fi module, Bluetooth function, sensor hub, or touch controller may depend on a shared regulator, clock, reset line, or GPIO-controlled power enable.

ACPI models some of these shared dependencies with PowerResource.

PowerResource (PWR1, 0x00, 0x0000)
{
    Method (_ON, 0, Serialized)
    {
        Store (One, PWEN)
        Sleep (10)
    }

    Method (_OFF, 0, Serialized)
    {
        Store (Zero, PWEN)
    }
}

Why PowerResource exists

Device power is not only D0/D3. A device may need:

  • a shared voltage rail
  • reset deassertion
  • clock enable
  • GPIO power enable
  • EC command
  • sequencing delay

PowerResource gives AML a way to describe power dependencies and transitions.

Item Value Note
PowerResource() Defines a shared power object Can be referenced by one or more devices.
_ON Turn resource on Usually enables GPIO/regulator/EC-controlled rail.
_OFF Turn resource off Must avoid breaking other active consumers.
_STA Resource status Can report whether the power resource is on.
_PR0 Resources needed for D0 Device references power resources needed when fully on.
_PR3 Resources related to D3 Device references resources for low-power/off state.

Debug Diary: camera missing after resume

Symptom:

Cold boot: camera works
After sleep/resume: camera missing
Driver error: device not responding

Possible ACPI path:

Resume
↓
OS powers device to D0
↓
_PR0 references PWR1
↓
PWR1._ON toggles GPIO power enable
↓
Reset delay too short or wrong GPIO polarity
↓
Camera fails probe

Common Pitfall: shared rail ownership

If two devices share one PowerResource, turning it off for one device can break the other.

Camera and sensor hub share PWR1
Camera enters low power
PWR1._OFF runs
Sensor hub unexpectedly loses power

PowerResource review checklist

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