drm/i915: Verify power domains after enabling them

After
commit 2cd9a689e9 ("drm/i915: Refactor intel_display_set_init_power() logic")
it makes more sense to check the power domain/well refcounts after
enabling the power domains functionality. Before that it's guaranteed
that most power wells (in the INIT domain) will have a reference held,
so not an interesting state.

While at it also add the check after the init_hw/fini_hw, disable and
suspend/resume steps. Make the test optional on a Kconfig option since
it may add substantial overhead: on VLV/CHV the corresponding PUNIT reg
access for each power well may take up to 20ms.

v2:
- Add the state check to more spots. (Chris)

v3:
- During suspend check the state before deiniting display core.
  Afterwards DC states are disabled (and so the dc_off power well is
  enabled) even though we don't hold a reference on it.
- Do the test conditionally based on a new Kconfig option. (Chris)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
[Add DRM_I915_DEBUG_RUNTIME_PM to welcome messages]
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180817145837.26592-1-imre.deak@intel.com

drivers/gpu/drm/i915/Kconfig.debug

@@ -30,6 +30,7 @@ config DRM_I915_DEBUG
 	select SW_SYNC # signaling validation framework (igt/syncobj*)
 	select DRM_I915_SW_FENCE_DEBUG_OBJECTS
 	select DRM_I915_SELFTEST
+	select DRM_I915_DEBUG_RUNTIME_PM
         default n
         help
           Choose this option to turn on extra driver debugging that may affect
@@ -167,3 +168,14 @@ config DRM_I915_DEBUG_VBLANK_EVADE
 	  the vblank.
 
 	  If in doubt, say "N".
+
+config DRM_I915_DEBUG_RUNTIME_PM
+	bool "Enable extra state checking for runtime PM"
+	depends on DRM_I915
+	default n
+	help
+	  Choose this option to turn on extra state checking for the
+	  runtime PM functionality. This may introduce overhead during
+	  driver loading, suspend and resume operations.
+
+	  If in doubt, say "N"