[PATCH v9 2/3] drm/debugfs: show lingering bridges

[Luca Ceresoli]

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 and lingering 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 lingering bridges to the /sys/kernel/debug/dri/bridges output.

Reviewed-by: Maxime Ripard <mrip...@kernel.org>
Signed-off-by: Luca Ceresoli <luca.ceres...@bootlin.com>
---

Changes in v9:
- rename leftover instances of "removed" to "lingering"

Changes in v8:
- updated to rename bridge_removed_list -> bridge_lingering_list

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 
9491ae7c884d355be4a82fb02a43a42d17fa8e0c..dda4e641a38fa38cef16296366eea08fe8702618
 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -1491,17 +1491,20 @@ 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 lingering)
 {
        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),
+                  lingering ? " [lingering]" : "");
 
        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 && !lingering)
                drm_printf(p, "\tOF: %pOFfc\n", bridge->of_node);
 
        drm_printf(p, "\tops: [0x%x]", bridge->ops);
@@ -1527,7 +1530,10 @@ 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_lingering_list, list)
+               drm_bridge_debugfs_show_bridge(&p, bridge, idx++, true);
 
        mutex_unlock(&bridge_lock);
 
@@ -1542,7 +1548,7 @@ 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;
 }

-- 
2.51.0