Debugging Embedded Linux (Kernel) Power Management – ELCE 2012

Tero Kristo, Linux kernel developer at Texas Instruments, explains how to debug power management in Embedded Linux at ELCE 2012.

Abstract:

The presentation will talk about debugging various problems a kernel developer can face when working with power management. These include hardware related issues (IC / HW layout bugs, bad documentation) and software related (kernel bugs, driver problems, adding new kernel features, bad userspace behavior.) Along with presenting some of these problems, I will discuss about ways to debug these… power management typically requires specific tools to be used. I will base the discussion on my first hand experience from working with Linux PM. Target audience is (kernel) software developers interested in power management.

The presentation is divided into 3 sections:

• Debugging tools / methods for PM
  • Disabling kernel features
  • Stress testing
  • Tracing (printk / low level UART)
  • GPIO / LED trace
  • Debugger
  • Buffered traces / statistics with trace-cmd & kernelshark
• Kernel power management features
  • Suspend – echo mem > /sys/power/state
  • Cpuidle – Debug info available at /sys/devices/system/cpu/*/cpuidle/*
  • Regulators – Userspace API available at /sys/class/regulator
  • Clock framework – Userspace interface: /sys/kernel/debug/clk/*
  • Cpufreq – Debug info in /sys/devices/system/cpu/*/cpufreq/*, /sys/class/regulator/* and /sys/kernel/debug/clk/
  • Devfreq
• Typical power management problems / bugs
  • Bootloader madness insanity
  • Device crash
  • Device malfunction
  • Increased power consumption – Can be kernel, hardware or userspace issues

You can  download the slides for this presentation, and you may also want to have a look at Powertop & Powerdebug for Linux power management debugging.

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