subsys:pm:pm.c Extend checking for next event adding custom hook

[msmttchr]

Proposal: Extend Zephyr PM to Support Custom Next Event Ticks via Hook

Background

In Zephyr’s power management, the function pm_system_suspend determines the next system wake-up time by considering kernel ticks and an optional custom event list. This event list is typically populated on an event-driven basis whenever events change.

However, certain use cases involve proprietary or complex data sources for the next event timing that cannot be easily or practically translated into entries in the event list. Examples include:

• Timing information stored in hardware registers.
• Proprietary binary code modules where source modification is impractical.
• Complex data structures that are inefficient to convert into event list format.

Proposal

Introduce a new optional hook, pm_policy_next_custom_ticks(), which allows retrieving the next event ticks directly from a custom source. This hook will be called during the suspend decision process to complement the existing kernel and event list ticks.

Implementation

In pm_system_suspend, extend the tick calculation as follows:

/*
 * Determine the earliest tick count among kernel ticks, event list ticks,
 * and optionally, custom ticks provided by a user-defined hook.
 */
events_ticks = pm_policy_next_event_ticks();
ticks = ticks_expiring_sooner(kernel_ticks, events_ticks);

#ifdef CONFIG_PM_CUSTOM_TICKS_HOOK
extern int64_t pm_policy_next_custom_ticks(int64_t current_ticks); /* Declaration in policy.h */
ticks = ticks_expiring_sooner(pm_policy_next_custom_ticks(ticks), ticks);
#endif

• pm_policy_next_custom_ticks(int64_t current_ticks) should return the next event tick count from the custom source, considering current_ticks as a reference or upper bound.
• The hook is enabled via CONFIG_PM_CUSTOM_TICKS_HOOK Kconfig option.
• This extension maintains backward compatibility, as the hook is optional.

Benefits

• Enables integration with proprietary or hardware-specific timing sources.
• Avoids costly or impractical translation of complex event data into the event list.
• Increases flexibility and extensibility of Zephyr’s power management framework.

@ceolin, any possible unwanted side effects ?