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

Luca Ceresoli
2025-02-06T18:15:38Z

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@bootlin.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