linux-kernel - [PATCH v7 3/3] drm/debugfs: show removed bridges

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Message-Id: <20250819-drm-bridge-debugfs-removed-v7-3-970702579978@bootlin.com>
Date: Tue, 19 Aug 2025 11:42:12 +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: Hui Pu <Hui.Pu@...ealthcare.com>, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 Luca Ceresoli <luca.ceresoli@...tlin.com>, 
 Dmitry Baryshkov <lumag@...nel.org>
Subject: [PATCH v7 3/3] drm/debugfs: show removed bridges

The usefulness of /sys/kernel/debug/dri/bridges is limited as it only shows
bridges between drm_bridge_add() and drm_bridge_remove(). However
refcounted bridges can stay allocated for a long time after
drm_bridge_remove(), and a memory leak due to a missing drm_bridge_put()
would not be visible in this debugfs file.

Add removed bridges to the /sys/kernel/debug/dri/bridges output.

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

---

Changes in v7:
- rebased on current code which is in drm_bridge.c now
- removed if (drm_bridge_is_refcounted(bridge)), refcounting is not
  optional
- don't show bridge address
- improve commit message

This patch was added in v6.
---
 drivers/gpu/drm/drm_bridge.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 2e688ee14b9efbc810bcdb0ab7ecd4b688be8299..4e9ad8a198e357c448b82a1ff5e07e558a6168d6 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -1498,17 +1498,20 @@ EXPORT_SYMBOL(devm_drm_put_bridge);
 
 static void drm_bridge_debugfs_show_bridge(struct drm_printer *p,
 					   struct drm_bridge *bridge,
-					   unsigned int idx)
+					   unsigned int idx,
+					   bool removed)
 {
 	drm_printf(p, "bridge[%u]: %ps\n", idx, bridge->funcs);
 
-	drm_printf(p, "\trefcount: %u\n", kref_read(&bridge->refcount));
+	drm_printf(p, "\trefcount: %u%s\n", kref_read(&bridge->refcount),
+		   removed ? " [removed]" : "");
 
 	drm_printf(p, "\ttype: [%d] %s\n",
 		   bridge->type,
 		   drm_get_connector_type_name(bridge->type));
 
-	if (bridge->of_node)
+	/* The OF node could be freed after drm_bridge_remove() */
+	if (bridge->of_node && !removed)
 		drm_printf(p, "\tOF: %pOFfc\n", bridge->of_node);
 
 	drm_printf(p, "\tops: [0x%x]", bridge->ops);
@@ -1534,7 +1537,10 @@ static int allbridges_show(struct seq_file *m, void *data)
 	mutex_lock(&bridge_lock);
 
 	list_for_each_entry(bridge, &bridge_list, list)
-		drm_bridge_debugfs_show_bridge(&p, bridge, idx++);
+		drm_bridge_debugfs_show_bridge(&p, bridge, idx++, false);
+
+	list_for_each_entry(bridge, &bridge_removed_list, list)
+		drm_bridge_debugfs_show_bridge(&p, bridge, idx++, true);
 
 	mutex_unlock(&bridge_lock);
 
@@ -1549,7 +1555,7 @@ static int encoder_bridges_show(struct seq_file *m, void *data)
 	unsigned int idx = 0;
 
 	drm_for_each_bridge_in_chain_scoped(encoder, bridge)
-		drm_bridge_debugfs_show_bridge(&p, bridge, idx++);
+		drm_bridge_debugfs_show_bridge(&p, bridge, idx++, false);
 
 	return 0;
 }

-- 
2.50.1