drm/panel: Add prepare_prev_first flag to drm_panel

Mapping to the drm_bridge flag pre_enable_prev_first,
add a new flag prepare_prev_first to drm_panel to allow
the panel driver to request that the upstream bridge should
be pre_enabled before the panel prepare.
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20221205173328.1395350-6-dave.stevenson@raspberrypi.comSigned-off-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/bridge/panel.c

@@ -364,6 +364,8 @@ struct drm_bridge *devm_drm_panel_bridge_add_typed(struct device *dev,
 		devres_free(ptr);
 	}
 
+	bridge->pre_enable_prev_first = panel->prepare_prev_first;
+
 	return bridge;
 }
 EXPORT_SYMBOL(devm_drm_panel_bridge_add_typed);

include/drm/drm_panel.h

@@ -188,6 +188,16 @@ struct drm_panel {
 	 * Panel entry in registry.
 	 */
 	struct list_head list;
+
+	/**
+	 * @prepare_prev_first:
+	 *
+	 * The previous controller should be prepared first, before the prepare
+	 * for the panel is called. This is largely required for DSI panels
+	 * where the DSI host controller should be initialised to LP-11 before
+	 * the panel is powered up.
+	 */
+	bool prepare_prev_first;
 };
 
 void drm_panel_init(struct drm_panel *panel, struct device *dev,