linux-kernel - [PATCH] drm/bridge: drm_bridge_get/put(): document NULL pointer behaviour

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Message-Id: <20260129-drm-bridge-alloc-getput-document-null-check-v1-1-2e5334b9e78e@bootlin.com>
Date: Thu, 29 Jan 2026 10:30:52 +0100
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: Liu Ying <victor.liu@....com>, Hui Pu <Hui.Pu@...ealthcare.com>, 
 Ian Ray <ian.ray@...ealthcare.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] drm/bridge: drm_bridge_get/put(): document NULL pointer
 behaviour

drm_bridge_get and drm_bridge_put() do nothing when they are passed a NULL
pointer, and they do so since their initial addition in commit 30d1b37d4c02
("drm/bridge: add support for refcounting").

This allows simpler code in various places when using these
functions. However it's not documented, so it's not clear whether it is
part of the API "contract" or just a current implementation detail that
might change in the future.

There is no visible reason to remove this NULL check, so document it,
making it part of the contract, letting users count on it.

Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
---
Historical note: I thought this was documented from the beginning and
realized it's not the case when someone proposed adding a 'if (bridge)
drm_bridge_put(bridge)' to a driver [0]. Let's fix it now.

[0] https://lore.kernel.org/lkml/DG0CHD0TAH9A.27UW4KKY2O9V7@bootlin.com/
---
 drivers/gpu/drm/drm_bridge.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 3b165a0d1e77..3108249a63cd 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -282,7 +282,7 @@ static void __drm_bridge_free(struct kref *kref)
 
 /**
  * drm_bridge_get - Acquire a bridge reference
- * @bridge: DRM bridge
+ * @bridge: DRM bridge; if NULL this function does nothing
  *
  * This function increments the bridge's refcount.
  *
@@ -300,7 +300,7 @@ EXPORT_SYMBOL(drm_bridge_get);
 
 /**
  * drm_bridge_put - Release a bridge reference
- * @bridge: DRM bridge
+ * @bridge: DRM bridge; if NULL this function does nothing
  *
  * This function decrements the bridge's reference count and frees the
  * object if the reference count drops to zero.

---
base-commit: a50007089e078a1b7a826559a02277b1601ee189
change-id: 20260129-drm-bridge-alloc-getput-document-null-check-a551e64b8fc1

Best regards,
-- 
Luca Ceresoli <luca.ceresoli@...tlin.com>