linux-kernel - [PATCH v5] drm/bridge: imx8qxp-pixel-link: get/put the next bridge

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Message-Id: <20260203-drm-bridge-alloc-getput-drm_of_find_bridge-v5-1-66bda8d617b4@bootlin.com>
Date: Tue, 03 Feb 2026 11:35:25 +0100
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Liu Ying <victor.liu@....com>, Andrzej Hajda <andrzej.hajda@...el.com>, 
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, 
 Pengutronix Kernel Team <kernel@...gutronix.de>, 
 Fabio Estevam <festevam@...il.com>
Cc: Hui Pu <Hui.Pu@...ealthcare.com>, Ian Ray <ian.ray@...ealthcare.com>, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 dri-devel@...ts.freedesktop.org, imx@...ts.linux.dev, 
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 Luca Ceresoli <luca.ceresoli@...tlin.com>
Subject: [PATCH v5] drm/bridge: imx8qxp-pixel-link: get/put the next bridge

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. 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, get a reference for
each pointer that stores a drm_bridge address when it is stored and release
it when the pointer is overwritten or goes out of scope. Also remove the
intermediate selected_bridge variable to reduce the refcounted variables in
the function. The involved pointers are:

 * next_bridge loop-local variable:
   - get reference by of_drm_find_and_get_bridge()
   - put reference at the end of the loop iteration (__free)

 * pl->bridge.next_bridge, tied to struct imx8qxp_pixel_link lifetime:
   - get reference when assigned (by copy from next_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)

Additionally, split the somewhat complex if() for readability.

Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>

---

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 | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 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..e29e099b893a 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;
@@ -297,7 +295,8 @@ static int imx8qxp_pixel_link_find_next_bridge(struct imx8qxp_pixel_link *pl)
 			continue;
 		}
 
-		struct drm_bridge *next_bridge = of_drm_find_bridge(remote);
+		struct drm_bridge *next_bridge __free(drm_bridge_put) =
+			of_drm_find_and_get_bridge(remote);
 		if (!next_bridge)
 			return -EPROBE_DEFER;
 
@@ -305,12 +304,16 @@ static int imx8qxp_pixel_link_find_next_bridge(struct imx8qxp_pixel_link *pl)
 		 * 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)
+			pl->bridge.next_bridge = drm_bridge_get(next_bridge);
+
+		if (of_property_present(remote, "fsl,companion-pxl2dpi")) {
+			drm_bridge_put(pl->bridge.next_bridge);
+			pl->bridge.next_bridge = drm_bridge_get(next_bridge);
+		}
 	}
 
 	pl->mst_addr = port_id - 1;
-	pl->next_bridge = selected_bridge;
 
 	return 0;
 }

-- 
2.52.0