Suspend

Low-power bugs often look intermittent: the first I/O after idle fails, interrupts disappear after wakeup, /dev still exists but hardware does not respond, or power never goes down.

These problems often come from the Linux driver power-management state machine.

Embedded Linux drivers commonly face two paths: runtime PM and system suspend/resume. Both save power, but they solve different problems.

The safest first model is this: runtime PM handles per-device idle power saving while the system is running; system suspend/resume handles whole-system sleep and wakeup. A driver must keep I/O, resources, wakeup sources, and state restore consistent in both paths.