Why Won't My CPU Sleep? Debugging CPUIdle Mysteries on ARM SoCs
summary
ARM64 systems fail to reach or exit deep CPU idle when device tree idle states are missing or firmware rejects PSCI parameters; adding a DT idle entry and implementing PSCI validate_power_state in Trusted Firmware fixes the first failure, while adding an always-on clock event provider and extending the timer driver lets CPUIdle pick deeper states despite a local-timer-stop flag. Debugging uses trace-cmd + KernelShark, Perfetto, trace_printk and GPIO logic-analyzer toggles; the fixes are upstream and suspend-to-idle then works (zero wake activity in traces).
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chapters (9)
- 0:00Introduction and context
- 3:16CPU idle fundamentals
- 4:30Case study one: initial setup
- 14:55PSCI and firmware basics
- 18:03Case study two: deep sleep
- 30:41Device tree configuration
- 36:26Case study three: wakeup
- 38:50Debugging tools and methods
- 41:58Future work and conclusion
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