drm/atomic-helper: Don't call atomic_update_plane when it stays off

It's a silly thing to do and surprises driver writers. Most likely
this did already blow up for exynos.

It's also a silly thing to change plane state when it's off, but fbdev
is silly (it does an unconditional modeset over all planes). And
userspace can be evil. So I think we need this.

With this check in the helpers we can remove the one in i915 code for
the same conditions (becuase ->crtc iff ->fb).

Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: dri-devel@lists.freedesktop.org
Cc: Inki Dae <inki.dae@samsung.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

drivers/gpu/drm/drm_atomic_helper.c

@@ -1138,7 +1138,8 @@ void drm_atomic_helper_commit_planes(struct drm_device *dev,
 		if (drm_atomic_plane_disabling(plane, old_plane_state) &&
 		    funcs->atomic_disable)
 			funcs->atomic_disable(plane, old_plane_state);
-		else
+		else if (plane->state->crtc ||
+			 drm_atomic_plane_disabling(plane, old_plane_state))
 			funcs->atomic_update(plane, old_plane_state);
 	}
 

drivers/gpu/drm/i915/intel_atomic_plane.c

@@ -172,10 +172,6 @@ static void intel_plane_atomic_update(struct drm_plane *plane,
 	struct intel_plane_state *intel_state =
 		to_intel_plane_state(plane->state);
 
-	/* Don't disable an already disabled plane */
-	if (!plane->state->fb && !old_state->fb)
-		return;
-
 	intel_plane->commit_plane(plane, intel_state);
 }