linux-kernel - [PATCH v6 22/26] drm/debugfs: show removed bridges

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Message-Id: <20250206-hotplug-drm-bridge-v6-22-9d6f2c9c3058@bootlin.com>
Date: Thu, 06 Feb 2025 19:14:37 +0100
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Simona Vetter <simona@...ll.ch>, Inki Dae <inki.dae@...sung.com>, 
 Jagan Teki <jagan@...rulasolutions.com>, 
 Marek Szyprowski <m.szyprowski@...sung.com>, 
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
 Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, 
 Pengutronix Kernel Team <kernel@...gutronix.de>, 
 Fabio Estevam <festevam@...il.com>, Daniel Thompson <danielt@...nel.org>, 
 Andrzej Hajda <andrzej.hajda@...el.com>, Jonathan Corbet <corbet@....net>, 
 Sam Ravnborg <sam@...nborg.org>, Boris Brezillon <bbrezillon@...nel.org>, 
 Nicolas Ferre <nicolas.ferre@...rochip.com>, 
 Alexandre Belloni <alexandre.belloni@...tlin.com>, 
 Claudiu Beznea <claudiu.beznea@...on.dev>, 
 Jessica Zhang <quic_jesszhan@...cinc.com>
Cc: Paul Kocialkowski <contact@...lk.fr>, 
 Maxime Ripard <mripard@...nel.org>, 
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, 
 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>, 
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
 Hervé Codina <herve.codina@...tlin.com>, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
 linux-doc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
 Paul Kocialkowski <paul.kocialkowski@...tlin.com>, 
 Luca Ceresoli <luca.ceresoli@...tlin.com>
Subject: [PATCH v6 22/26] drm/debugfs: show removed bridges

The usefulness of /sys/kernel/debug/dri/bridges is limited as it only shows
bridges betweeb drm_bridge_add() and drm_bridge_remove(). However
refcounted bridges can stay allocated for way longer, 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.

Now however if a bridge is added and removed multiple times (as in
hot-pluggable hardware) and not freed immediately, there would be multiple
identical entries for the same bridge model/driver. To distinguish between
each instance add the bridge pointer to the output.

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

---

This patch was added in v6.
---
 drivers/gpu/drm/drm_debugfs.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_debugfs.c b/drivers/gpu/drm/drm_debugfs.c
index 629074247ffec4fa18df7af2d9023255abed501c..b04e1fba8faf7320794277c2017c97216320f017 100644
--- a/drivers/gpu/drm/drm_debugfs.c
+++ b/drivers/gpu/drm/drm_debugfs.c
@@ -740,12 +740,16 @@ void drm_debugfs_crtc_remove(struct drm_crtc *crtc)
 	crtc->debugfs_entry = NULL;
 }
 
-static void bridge_print(struct drm_printer *p, struct drm_bridge *bridge, unsigned int idx)
+static void bridge_print(struct drm_printer *p, struct drm_bridge *bridge, unsigned int idx,
+			 bool removed)
 {
 	drm_printf(p, "bridge[%u]: %ps\n", idx, bridge->funcs);
 
+	drm_printf(p, "\taddr: %p\n", bridge);
+
 	if (drm_bridge_is_refcounted(bridge))
-		drm_printf(p, "\trefcount: %u\n", kref_read(&bridge->refcount));
+		drm_printf(p, "\trefcount: %u%s\n", kref_read(&bridge->refcount),
+			   removed ? " [removed]" : "");
 	else
 		drm_printf(p, "\trefcount: N/A\n");
 
@@ -753,7 +757,8 @@ static void bridge_print(struct drm_printer *p, struct drm_bridge *bridge, unsig
 		   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);
@@ -778,7 +783,7 @@ static int bridges_show(struct seq_file *m, void *data)
 	unsigned int idx = 0;
 
 	drm_for_each_bridge_in_chain(encoder, bridge)
-		bridge_print(&p, bridge, idx++);
+		bridge_print(&p, bridge, idx++, false);
 
 	return 0;
 }
@@ -822,7 +827,10 @@ static int allbridges_show(struct seq_file *m, void *data)
 	mutex_lock(&bridge_lock);
 
 	list_for_each_entry(bridge, &bridge_list, list)
-		bridge_print(&p, bridge, idx++);
+		bridge_print(&p, bridge, idx++, false);
+
+	list_for_each_entry(bridge, &bridge_removed_list, list)
+		bridge_print(&p, bridge, idx++, true);
 
 	mutex_unlock(&bridge_lock);
 

-- 
2.34.1