drm/omap: Use normalized zpos for plane placement

Planes with identical zpos value will result undefined behavior:
disappearing planes, screen flickering and it is not supported by the
hardware.

Use normalized zpos to make sure that we don't encounter invalid
configuration.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
CC: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180321102029.15248-7-peter.ujfalusi@ti.com

drivers/gpu/drm/omapdrm/omap_drv.c

@@ -319,6 +319,9 @@ static int omap_modeset_init(struct drm_device *dev)
 	dev->mode_config.max_width = 8192;
 	dev->mode_config.max_height = 8192;
 
+	/* We want the zpos to be normalized */
+	dev->mode_config.normalize_zpos = true;
+
 	dev->mode_config.funcs = &omap_mode_config_funcs;
 	dev->mode_config.helper_private = &omap_mode_config_helper_funcs;
 

drivers/gpu/drm/omapdrm/omap_plane.c

@@ -65,7 +65,7 @@ static void omap_plane_atomic_update(struct drm_plane *plane,
 	info.rotation_type = OMAP_DSS_ROT_NONE;
 	info.rotation = DRM_MODE_ROTATE_0;
 	info.global_alpha = 0xff;
-	info.zorder = state->zpos;
+	info.zorder = state->normalized_zpos;
 
 	/* update scanout: */
 	omap_framebuffer_update_scanout(state->fb, state, &info);