Qualify the MCU’s debug state, the probe’s electrical connections, and the firmware’s instrumentation independently. Closing the debugger window does not prove that all three returned to their production condition. On nRF52840, a debug power request can change the meaning of a System OFF experiment, so the resulting current cannot simply be corrected by subtracting a…
Compare the USB configuration descriptor, the host’s successful remote-wakeup feature request, and the device controller’s actual signaling path before blaming a host that stays asleep. These are separate pieces of evidence. A device can advertise remote wakeup and remember host permission while its selected driver still lacks the software operation needed to initiate it. Applicability:…
A device can return its runtime-PM usage count to zero and still miss every apparent autosuspend opportunity because its last-busy timestamp keeps moving. Trace the timestamp updates and autosuspend requests together. Do not diagnose a reference leak from active status alone, and do not shorten the delay until the source of the updates is understood….
Make resume dependencies explicit in both topology and callback phase. Linux can order a child after its parent and a consumer after a declared supplier, but that does not make a resource initialized in a later phase available to an earlier callback. Diagnose the first invalid dependency edge instead of adding an arbitrary delay. Applicability:…
Diagnose a non-waking device by recording three distinct Linux facts: the driver declares wake capability, policy currently permits system wake, and the IRQ or bus wake mechanism was actually armed for the selected sleep state. A working runtime interrupt or a successful sysfs write proves less than this complete chain. Applicability: this guide pins device…
Disabling a shared regulator should release one consumer’s requirement, not force the physical rail off. Keep each consumer’s successful enable calls balanced with its own disables, then verify that another active consumer remains functional. A rail that stays on after one release may be exactly correct. Applicability: the API contract is Linux v6.12 with the…
A device passing autosuspend tests has not yet passed system-suspend tests. Runtime PM manages an individual device while the system continues running. System sleep coordinates a wider transition, with different callback phases, resource availability, and wake policy. Test both paths from both active and already runtime-suspended starting states. Applicability: this procedure uses Linux v6.12 device…
Use the Linux wakeup_count handshake to detect when a userspace sleep decision became stale before system suspend. Read a count, evaluate and prepare the policy decision, then write back that same count. If the write fails, do not request sleep on the old decision. If it succeeds, the kernel checks for newly reported wakeup events…
Find a runtime-PM reference leak by accounting for each operation’s acquired reference and its release on every terminal path. A device remaining active is a symptom, not proof of a leak. Separate an unbalanced usage count from autosuspend timing, active children, policy constraints, and a callback that cannot suspend. Applicability: the helper semantics below are…
After reset, restore the intended configuration rather than replaying every byte previously written or read. Registers can contain persistent settings, transient commands, live status, calibration, and results. Some combine settings and actions in one byte. A safe recovery path classifies those fields, rebuilds allowed writes, and starts new work only through an explicit operation. Applicability:…