Differences between rtcwake and ChromeOS' suspend_stress_test

[marc-hb]

As requested by @ranj063

https://chromium.googlesource.com/chromiumos/platform/power_manager/+/stabilize-4537.147.B/tools/suspend_stress_test

Suspend differences

From https://chromium.googlesource.com/chromiumos/platform2/+/HEAD/power_manager/docs/suspend_resume.md

The process begins when powerd (or some other process) decides that the system should be suspended. Suspender receives a request to suspend the system and generates an ID corresponding to the request. It performs pre-suspend preparation, such as muting audio and turning off the panel backlight. Then, it emits a SuspendImminent D-Bus signal to announce the suspend request to other processes (particularly ones that have registered suspend delays).

If the suspend attempt fails, Suspender waits for ten seconds before running powerd_suspend again to retry. After ten failed retries, the system is shut down.

In the end powerd writes to /sys/power/state which compared to powerd is the only thing that rtcwake does.

Resume differences

strace shows that rtcwake performs two ioctl(/dev/rtc0): ioctl(3, RTC_RD_TIME,...) and ioctl(3, RTC_WKALM_SET,...)

Instead, the source of suspend_stress_test shell script shows it writes to /sys/class/rtc/wakealarm.

This is hopefully equivalent.

Hardware and firmware differences

• sof-test tests "desktop" Linux distros (mostly: Ubuntu) with either UEFI or custom coreboot whereas ChromeOS' suspend_stress_test tests... ChromeOS' Linux and production coreboot.

• Due to signature restrictions, sof-test tests prototype hardware (with the exception of Up boards) whereas suspend_stress_test tests production chromebooks.

cc:

• https://github.com/thesofproject/sof-test/issues?q=+label%3A%22suspend+resume%22+
• https://github.com/thesofproject/linux/issues?q=+label%3A%22suspend+resume%22+