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.

Based on similar work done by Laurent Pinchart for R-Car DU.
commit db5be3a7d6bd ("drm: rcar-du: Ensure correct suspend/resume
ordering with VSP")

Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Tommaso Merciai <tommaso.merciai.xr@bp.renesas.com>
---
v1->v2:
 - Collected Laurent Pinchart tag.
 - Added commit id of the similar work on R-Car DU.

 drivers/gpu/drm/renesas/rz-du/rzg2l_du_vsp.c | 16 ++++++++++++++++
 drivers/gpu/drm/renesas/rz-du/rzg2l_du_vsp.h |  2 ++
 2 files changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/renesas/rz-du/rzg2l_du_vsp.c b/drivers/gpu/drm/renesas/rz-du/rzg2l_du_vsp.c
index bd486377f037..eb626c3cc421 100644
--- a/drivers/gpu/drm/renesas/rz-du/rzg2l_du_vsp.c
+++ b/drivers/gpu/drm/renesas/rz-du/rzg2l_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>
@@ -293,6 +294,9 @@ static void rzg2l_du_vsp_cleanup(struct drm_device *dev, void *res)
 {
 	struct rzg2l_du_vsp *vsp = res;
 
+	if (vsp->link)
+		device_link_del(vsp->link);
+
 	put_device(vsp->vsp);
 }
 
@@ -317,6 +321,18 @@ int rzg2l_du_vsp_init(struct rzg2l_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;
diff --git a/drivers/gpu/drm/renesas/rz-du/rzg2l_du_vsp.h b/drivers/gpu/drm/renesas/rz-du/rzg2l_du_vsp.h
index 322eb80dcbaf..a22aaf0843ed 100644
--- a/drivers/gpu/drm/renesas/rz-du/rzg2l_du_vsp.h
+++ b/drivers/gpu/drm/renesas/rz-du/rzg2l_du_vsp.h
@@ -15,6 +15,7 @@
 #include <linux/scatterlist.h>
 
 struct device;
+struct device_link;
 struct drm_framebuffer;
 struct rzg2l_du_device;
 struct rzg2l_du_format_info;
@@ -29,6 +30,7 @@ struct rzg2l_du_vsp_plane {
 struct rzg2l_du_vsp {
 	unsigned int index;
 	struct device *vsp;
+	struct device_link *link;
 	struct rzg2l_du_device *dev;
 };
 
-- 
2.43.0