[PATCH v6] drm/bridge: imx8qxp-pixel-link: get/put the next bridge

[Luca Ceresoli]

This driver obtains a bridge pointer from of_drm_find_bridge() in the probe
function and stores it until driver removal. of_drm_find_bridge() is
deprecated, so move to of_drm_find_and_get_bridge() for the bridge to be
refcounted and use bridge->next_bridge to put the reference on
deallocation.

To keep the code as simple and reliable as possible remove the intermediate
next_bridge and selected_bridge variables.

Get/put operations on the remaining pointer is pl->bridge.next_bridge,
which is tied to the struct imx8qxp_pixel_link lifetime, are:
 - get reference when assigned (by of_drm_find_and_get_bridge())
 - put reference before reassignment if reassignment happens
 - put reference when the struct imx8qxp_pixel_link embedding the
   struct drm_bridge is destroyed (struct drm_bridge::next_bridge)

Signed-off-by: Luca Ceresoli <luca.ceresoli at bootlin.com>

---

Changes in v6:
- rewrite as suggested by Liu, removing the next_bridge pointer too
  and splitting the comment for maximum clarity
- adapt commit message accordingly

Changes in v5:
- rewrite commit message after Liu's review to clarify the per-pointer
  get/put idea
- split the if()s involved in selcting the bridge
- remove intermediate selected_bridge pointer
- removed Maxime's R-by, patch changed
---
 drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c | 27 ++++++++++++-------------
 1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c b/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c
index 91e4f4d55469..055b94d75eb6 100644
--- a/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c
+++ b/drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c
@@ -23,7 +23,6 @@
 
 struct imx8qxp_pixel_link {
 	struct drm_bridge bridge;
-	struct drm_bridge *next_bridge;
 	struct device *dev;
 	struct imx_sc_ipc *ipc_handle;
 	u8 stream_id;
@@ -140,7 +139,7 @@ static int imx8qxp_pixel_link_bridge_attach(struct drm_bridge *bridge,
 	}
 
 	return drm_bridge_attach(encoder,
-				 pl->next_bridge, bridge,
+				 pl->bridge.next_bridge, bridge,
 				 DRM_BRIDGE_ATTACH_NO_CONNECTOR);
 }
 
@@ -260,7 +259,6 @@ static int imx8qxp_pixel_link_find_next_bridge(struct imx8qxp_pixel_link *pl)
 {
 	struct device_node *np = pl->dev->of_node;
 	struct device_node *port;
-	struct drm_bridge *selected_bridge = NULL;
 	u32 port_id;
 	bool found_port = false;
 	int reg;
@@ -297,20 +295,21 @@ static int imx8qxp_pixel_link_find_next_bridge(struct imx8qxp_pixel_link *pl)
 			continue;
 		}
 
-		struct drm_bridge *next_bridge = of_drm_find_bridge(remote);
-		if (!next_bridge)
-			return -EPROBE_DEFER;
-
-		/*
-		 * Select the next bridge with companion PXL2DPI if
-		 * present, otherwise default to the first bridge
-		 */
-		if (!selected_bridge || of_property_present(remote, "fsl,companion-pxl2dpi"))
-			selected_bridge = next_bridge;
+		if (!pl->bridge.next_bridge) {
+			/* Select the first bridge by default... */
+			pl->bridge.next_bridge = of_drm_find_and_get_bridge(remote);
+			if (!pl->bridge.next_bridge)
+				return -EPROBE_DEFER;
+		} else if (of_property_present(remote, "fsl,companion-pxl2dpi")) {
+			/* ... but prefer the companion PXL2DPI if present */
+			drm_bridge_put(pl->bridge.next_bridge);
+			pl->bridge.next_bridge = of_drm_find_and_get_bridge(remote);
+			if (!pl->bridge.next_bridge)
+				return -EPROBE_DEFER;
+		}
 	}
 
 	pl->mst_addr = port_id - 1;
-	pl->next_bridge = selected_bridge;
 
 	return 0;
 }

-- 
2.52.0