Krzysztof Kozlowski [off-list ref] writes:

When resuming the system the power domain has to be powered on early so
any runtime PM aware devices could resume.

This fixes following scenario reproduced on Exynos DRM:
1. Power domain is off before suspending the system.
2. System is suspended to RAM.
3. Resuming starts. The Exynos DRM driver resume callback is called.
4. The Exynos DRM driver calls drm_helper_resume_force_mode which turns
   the screen on by calling exynos_dsi_dpms with DRM_MODE_DPMS_ON.

Dumb Q: if the device (and power domain) were off before (and during)
suspend, why are they being resumed?

Shouldn't the resume path restore things to the same state they were
before suspend?

Kevin