class IdlePowerThread

Returns true if the power thread should be scheduled instead of eligible work because it needs

to perform a transition or power management function.

Requests to transition from Offline to Active.

Returns:

- {ZX_OK, Offline} if the transition was successful.

- {ZX_OK, Active} if the current state was already Active.

- {ZX_ERR_BAD_STATE, current state} if the current state was not Active or Offline.

- {ZX_ERR_TIMED_OUT, Offline} if the current state was Offline and transition timeout

expired.

Requests to transition from Active to Offline.

After the transition completes, waits until the platform reports (via platform_get_cpu_state)

that the CPU is powered off or stopped. If the platform does not support querying CPU power

state, this wait is skipped. If the platform never reports that the CPU is powered off, this

waits until |timeout_at| (i.e. indefinitely, if |timeout_at| is ZX_TIME_INFINITE), logging a

message periodically.

Returns:

- {ZX_OK, Active} if the transition was successful.

- {ZX_OK, Offline} if the current state was already Offline.

- {ZX_ERR_BAD_STATE, current state} if the current state was not Active or Offline.

- {ZX_ERR_TIMED_OUT, Active} if the current state was Active and transition timeout expired.

Note that in this case the request is not withdrawn (once the CPU's idle/power thread has

begun to take it offline, it cannot be stopped), so the CPU may still go Offline later.

- {ZX_ERR_TIMED_OUT, starting state} if the transition completed, but the timeout expired

before the platform reported that the CPU was powered off. Note that in this case, the

CPU's state is Offline.

- {error, starting state} if the transition completed, but querying the CPU's power state

failed with |error|. Note that in this case, the CPU's state is Offline.

Attempts to transition all active CPUs from Active to Suspend until the specified resume time.

CPUs that are Offline before suspend will remain Offline after resume until explicitly

transitioned to Active.

Returns: The boot-time at which the suspend operation is formally considered to have started.

This value can be used in conjunction with timestamps recorded in wake events to decide whether

a wake vector became signaled before suspend had formally started, or not.

Attempts to suspend the entire system using platform_suspend_system until the specified resume

time.

Similar to |TransitionAllActiveToSuspend|, except that rather than transitioning the active

non-boot CPUs to Suspend, transitions them to Offline (powering them off). Once the platform

has confirmed that every one of them has powered off, the boot CPU is transitioned to Suspend

and its idle/power thread suspends the system with platform_suspend_system. If power off

cannot be confirmed for every CPU, the suspend operation is aborted. Upon resume, the non-boot

CPUs which were taken offline are brought back online. (If bringing a CPU back online fails,

a KERNEL_OOPS is logged and that CPU remains Offline until explicitly transitioned to Active.

Its timers are migrated to the boot CPU, but its queued DPCs and pinned threads remain with it

until it is brought back online.)

CPUs that are Offline before suspend will remain Offline after resume until explicitly

transitioned to Active.

If the platform does not support system suspend, or cannot report CPU power state (see

platform_get_cpu_state), this behaves like |TransitionAllActiveToSuspend|.

Returns: The boot-time at which the suspend operation is formally considered to have started.

This value can be used in conjunction with timestamps recorded in wake events to decide whether

a wake vector became signaled before suspend had formally started, or not.

Implements the run loop executed by the CPU's idle/power thread.

Called by mp_unplug_current_cpu() to complete last steps of taking the CPU offline.

Accessors to the underlying Thread instance.

Accessor to the global system suspend state.

The current or target high-level operational state of the CPU. The depth and type of

idle/suspend states depends inputs from other subsystems, such as timer and run queues and

system power targets.

TODO(https://fxbug.dev/42086705): Rationalize this state with mp active / online states.