drm/i915: Move the unclaimed mmio detection into the powerwell for KMS

Replace the large comment about requiring the powerwell for
intel_uncore_arm_unclaimed_mmio_detection() by moving the arming of the
mmio error detection into the powerwell held for modesetting. Thereby
also accomplishing the goal of only arming the mmio detection after a
full modeset.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170504115508.13571-1-chris@chris-wilson.co.uk
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -13121,8 +13121,16 @@ static void intel_atomic_commit_tail(struct drm_atomic_state *state)
 
 	drm_atomic_helper_commit_hw_done(state);
 
-	if (intel_state->modeset)
+	if (intel_state->modeset) {
+		/* As one of the primary mmio accessors, KMS has a high
+		 * likelihood of triggering bugs in unclaimed access. After we
+		 * finish modesetting, see if an error has been flagged, and if
+		 * so enable debugging for the next modeset - and hope we catch
+		 * the culprit.
+		 */
+		intel_uncore_arm_unclaimed_mmio_detection(dev_priv);
 		intel_display_power_put(dev_priv, POWER_DOMAIN_MODESET);
+	}
 
 	mutex_lock(&dev->struct_mutex);
 	drm_atomic_helper_cleanup_planes(dev, state);
@@ -13132,19 +13140,6 @@ static void intel_atomic_commit_tail(struct drm_atomic_state *state)
 
 	drm_atomic_state_put(state);
 
-	/* As one of the primary mmio accessors, KMS has a high likelihood
-	 * of triggering bugs in unclaimed access. After we finish
-	 * modesetting, see if an error has been flagged, and if so
-	 * enable debugging for the next modeset - and hope we catch
-	 * the culprit.
-	 *
-	 * XXX note that we assume display power is on at this point.
-	 * This might hold true now but we need to add pm helper to check
-	 * unclaimed only when the hardware is on, as atomic commits
-	 * can happen also when the device is completely off.
-	 */
-	intel_uncore_arm_unclaimed_mmio_detection(dev_priv);
-
 	intel_atomic_helper_free_state(dev_priv);
 }