drm: Add a plane->reset hook

In general having this can't hurt, and the atomic helpers will need
it to be able to reset the state objects properly. The overall idea
is to reset in the order pixels flow, so planes -> crtcs ->
encoders -> connectors.

v2: Squash in fixup from Ville to correctly deference struct drm_plane
instead of drm_crtc when walking the plane list. Fixes an oops in
driver init and resume.
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_crtc.c

@@ -4663,9 +4663,14 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
 void drm_mode_config_reset(struct drm_device *dev)
 {
 	struct drm_crtc *crtc;
+	struct drm_plane *plane;
 	struct drm_encoder *encoder;
 	struct drm_connector *connector;
 
+	list_for_each_entry(plane, &dev->mode_config.plane_list, head)
+		if (plane->funcs->reset)
+			plane->funcs->reset(plane);
+
 	list_for_each_entry(crtc, &dev->mode_config.crtc_list, head)
 		if (crtc->funcs->reset)
 			crtc->funcs->reset(crtc);

include/drm/drm_crtc.h

@@ -581,6 +581,7 @@ struct drm_plane_funcs {
 			    uint32_t src_w, uint32_t src_h);
 	int (*disable_plane)(struct drm_plane *plane);
 	void (*destroy)(struct drm_plane *plane);
+	void (*reset)(struct drm_plane *plane);
 
 	int (*set_property)(struct drm_plane *plane,
 			    struct drm_property *property, uint64_t val);