Board-level Linux integration, U-Boot, device trees, kernel drivers and peripheral bring-up. Separate power and hardware checks from software adaptation, and define a recoverable boot path.
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…
Clearing an endpoint halt repairs a USB transport condition. It does not by itself restore the device’s command parser, identify the outcome of the interrupted operation, or select the next legal protocol phase. Recovery must follow the endpoint type and the device class or vendor protocol. Applicability: Linux v6.12 host-driver APIs provide the implementation boundary….
USB disconnect must close the submission path, finish or cancel outstanding requests, and drain their callbacks before releasing the state those callbacks use. Cancelling a transfer is not the same as waiting for its completion handler. An open file or queued work item can also outlive the physical device. Applicability: this guide targets Linux v6.12…
Keep the number of original scatterlist entries separate from the number of DMA segments returned by mapping. Program hardware from the mapped representation, but pass the original entry count to the corresponding unmap and scatterlist synchronization calls. Reusing one variable for both counts hides a portability bug when the mapping layer merges entries. Applicability: this…
When DMA works only for some allocations, compare the address the device receives with its documented addressing capability. A CPU pointer, a CPU physical address, and a DMA address are different quantities. Fix the mask, mapping, or descriptor encoding contract before moving buffers into a conveniently low region and calling the problem solved. Applicability: this…
A safe steady-state GPIO value does not prove a safe boot handover. Treat reset defaults, firmware configuration, kernel pinctrl selection, and driver initialization as separate transitions. At every boundary, identify which block owns the pad and which value becomes visible when its output path is connected. Applicability: this procedure uses Linux v6.12 pinctrl and GPIO…
A PWM request describes the desired waveform, not a measurement of the waveform the hardware produced. Check the driver’s quantization and state-reporting contract, then capture period, active time, polarity, and disabled behavior at the relevant output. A successful apply call or matching cached state cannot establish exact timing or a safe inactive level. Applicability: the…