linux-kernel - [PATCH 2/3] drm/bridge: get/put the bridge reference in drm_bridge

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Message-Id: <20250620-drm-bridge-alloc-getput-drm-bridge-c-v1-2-bad7eba5d117@bootlin.com>
Date: Fri, 20 Jun 2025 11:32:07 +0200
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: 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>
Cc: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>, 
 Anusha Srivatsa <asrivats@...hat.com>, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 Luca Ceresoli <luca.ceresoli@...tlin.com>
Subject: [PATCH 2/3] drm/bridge: get/put the bridge reference in
 drm_bridge_attach/detach()

drm_bridge_attach() adds the bridge to the encoder chain, so take a
reference for that. Vice versa in drm_bridge_detach().

Reviewed-by: Maxime Ripard <mripard@...nel.org>
Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
---

Changes in v8: none

Changes in v7:
- in v6 this was part of "drm/bridge: add support for refcounted DRM
  bridges", now split to a separate patch
---
 drivers/gpu/drm/drm_bridge.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index fa2b2457b16e145e3ace70c53984937096d310d0..f001bbe95559aabf0aac9f25f89250ad4e1ad9c8 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -411,11 +411,17 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
 	if (!encoder || !bridge)
 		return -EINVAL;
 
-	if (previous && (!previous->dev || previous->encoder != encoder))
-		return -EINVAL;
+	drm_bridge_get(bridge);
 
-	if (bridge->dev)
-		return -EBUSY;
+	if (previous && (!previous->dev || previous->encoder != encoder)) {
+		ret = -EINVAL;
+		goto err_put_bridge;
+	}
+
+	if (bridge->dev) {
+		ret = -EBUSY;
+		goto err_put_bridge;
+	}
 
 	bridge->dev = encoder->dev;
 	bridge->encoder = encoder;
@@ -464,6 +470,8 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
 			      "failed to attach bridge %pOF to encoder %s\n",
 			      bridge->of_node, encoder->name);
 
+err_put_bridge:
+	drm_bridge_put(bridge);
 	return ret;
 }
 EXPORT_SYMBOL(drm_bridge_attach);
@@ -484,6 +492,7 @@ void drm_bridge_detach(struct drm_bridge *bridge)
 
 	list_del(&bridge->chain_node);
 	bridge->dev = NULL;
+	drm_bridge_put(bridge);
 }
 
 /**

-- 
2.49.0