drm/i915: Don't flag both full modeset and fastset at the same time

Be consistent in whether we flag a full modeset or a
fastset for the pipe. intel_modeset_all_pipes() would
seem to be the only codepath not getting this right.

The other case is when we flag the fastset initially,
currently we just clear the mode_changed flag and set
the update_pipe flag. But we could still have
connectors_changed==true or active_changed==true forcing
a full modeset anyway. So check for that after clearing
the mode_changed flag.

And let's add a WARN to make sure we did get it right.

v2: Deal with {connectors,active}_changed

Reviewed-by: Jani Nikula <jani.nikula@intel.com> #v1
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221021162442.27283-4-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/display/intel_display.c

@@ -5939,6 +5939,7 @@ int intel_modeset_all_pipes(struct intel_atomic_state *state,
 			    crtc->base.base.id, crtc->base.name, reason);
 
 		crtc_state->uapi.mode_changed = true;
+		crtc_state->update_pipe = false;
 
 		ret = drm_atomic_add_affected_connectors(&state->base,
 							 &crtc->base);
@@ -6114,7 +6115,8 @@ static void intel_crtc_check_fastset(const struct intel_crtc_state *old_crtc_sta
 		return;
 
 	new_crtc_state->uapi.mode_changed = false;
-	new_crtc_state->update_pipe = true;
+	if (!intel_crtc_needs_modeset(new_crtc_state))
+		new_crtc_state->update_pipe = true;
 }
 
 static int intel_crtc_add_planes_to_state(struct intel_atomic_state *state,
@@ -6890,6 +6892,11 @@ static int intel_atomic_check(struct drm_device *dev,
 		if (ret)
 			goto fail;
 
+		/* Either full modeset or fastset (or neither), never both */
+		drm_WARN_ON(&dev_priv->drm,
+			    intel_crtc_needs_modeset(new_crtc_state) &&
+			    intel_crtc_needs_fastset(new_crtc_state));
+
 		if (!intel_crtc_needs_modeset(new_crtc_state) &&
 		    !intel_crtc_needs_fastset(new_crtc_state))
 			continue;