drm: rcar-du: Ensure correct suspend/resume ordering with VSP

The VSP serves as an interface to memory and a compositor to the DU. It
therefore needs to be suspended after and resumed before the DU, to be
properly stopped and restarted in a controlled fashion driven by the DU
driver. This currently works by chance. Avoid relying on luck by
enforcing the correct suspend/resume ordering with device links.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Tested-by: Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com>
Reviewed-by: Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com>
Link: https://patch.msgid.link/20260323164526.2292491-2-laurent.pinchart+renesas@ideasonboard.com
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>

Author: Laurent Pinchart

drivers/gpu/drm/renesas/rcar-du/rcar_du_vsp.c

@@ -20,6 +20,7 @@
 #include <drm/drm_vblank.h>
 
 #include <linux/bitops.h>
+#include <linux/device.h>
 #include <linux/dma-mapping.h>
 #include <linux/of_platform.h>
 #include <linux/platform_device.h>
@@ -458,6 +459,9 @@ static void rcar_du_vsp_cleanup(struct drm_device *dev, void *res)
 
 	kfree(vsp->planes);
 
+	if (vsp->link)
+		device_link_del(vsp->link);
+
 	put_device(vsp->vsp);
 }
 
@@ -482,6 +486,18 @@ int rcar_du_vsp_init(struct rcar_du_vsp *vsp, struct device_node *np,
 	if (ret < 0)
 		return ret;
 
+	/*
+	 * Enforce suspend/resume ordering between the DU (consumer) and the
+	 * VSP (supplier). The DU will be suspended before and resume after the
+	 * VSP.
+	 */
+	vsp->link = device_link_add(rcdu->dev, vsp->vsp, DL_FLAG_STATELESS);
+	if (!vsp->link) {
+		dev_err(rcdu->dev, "Failed to create device link to VSP %s\n",
+			dev_name(vsp->vsp));
+		return -EINVAL;
+	}
+
 	ret = vsp1_du_init(vsp->vsp);
 	if (ret < 0)
 		return ret;

drivers/gpu/drm/renesas/rcar-du/rcar_du_vsp.h

@@ -12,6 +12,7 @@
 
 #include <drm/drm_plane.h>
 
+struct device_link;
 struct drm_framebuffer;
 struct rcar_du_format_info;
 struct rcar_du_vsp;
@@ -26,6 +27,7 @@ struct rcar_du_vsp_plane {
 struct rcar_du_vsp {
 	unsigned int index;
 	struct device *vsp;
+	struct device_link *link;
 	struct rcar_du_device *dev;
 	struct rcar_du_vsp_plane *planes;
 	unsigned int num_planes;