Ulf Hansson [off-list ref] writes:

If the PM domain is powered off when the first device starts its system PM
prepare phase, genpd prevents any further attempts to power on the PM
domain during the following system PM phases. Not until the system PM
complete phase is finalized for all devices in the PM domain, genpd again
allows it to be powered on.

This behaviour needs to be changed, as a subsystem/driver for a device in
the same PM domain may still need to be able to serve requests in some of
the system PM phases. Accordingly, it may need to runtime resume its
device and thus also request the corresponding PM domain to be powered on.

To deal with these scenarios, let's make the device operational in the
system PM prepare phase by runtime resuming it, no matter if the PM domain
is powered on or off. Changing this also enables us to remove genpd's
suspend_power_off flag, as it's being used to track this condition.
Additionally, we must allow the PM domain to be powered on via runtime PM
during the system PM phases.

This change also requires a fix in the AMD ACP (Audio CoProcessor) drm
driver. It registers a genpd to model the ACP as a PM domain, but
unfortunately it's also abuses genpd's "internal" suspend_power_off flag
to deal with a corner case at system PM resume.

More precisely, the so called SMU block powers on the ACP at system PM
resume, unconditionally if it's being used or not. This may lead to that
genpd's internal status of the power state, may not correctly reflect the
power state of the HW after a system PM resume.

Because of changing the behaviour of genpd, by runtime resuming devices in
the prepare phase, the AMD ACP drm driver no longer have to deal with this
corner case. So let's just drop the related code in this driver.

Cc: David Airlie <redacted>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Maruthi Srinivas Bayyavarapu <redacted>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Ulf Hansson <redacted>
---

Changes in v3:
	- Updated changelog.

Changes in v2:
	- Updated changelog.
	- Added a fix in the AMD ACP (Audio CoProcessor) drm driver, which
	registers a genpd. The fix removes the usage of genpd's internal
	suspend_power_off flag as it's not needed after this change. Because of
	this change I am also requesting an ack from the drm driver maintainer.


---
 drivers/base/power/domain.c             | 84 ++++++++++++---------------------
 drivers/gpu/drm/amd/amdgpu/amdgpu_acp.c | 23 ---------
 include/linux/pm_domain.h               |  1 -

For the PM core part:

Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Acked-by: Kevin Hilman <khilman@baylibre.com>

For the AMD DRM driver, the changes look right too, but I'm not
confident enough about the intent of that to be sure.

Kevin