linux-kernel - [PATCH 3/4] drm/bridge: document that adding a bridge is mandatory before attach

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Message-Id: <20251003-b4-drm-bridge-alloc-add-before-attach-v1-3-92fb40d27704@bootlin.com>
Date: Fri, 03 Oct 2025 10:59:57 +0200
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Alain Volmat <alain.volmat@...s.st.com>, 
 Raphael Gallais-Pou <rgallaispou@...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>, 
 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>
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>
Subject: [PATCH 3/4] drm/bridge: document that adding a bridge is mandatory
 before attach

At the moment it's not documented that you need to add a bridge before
attaching it. Clarify that.

Suggested-by: Maxime Ripard <mripard@...nel.org>
Link: https://lore.kernel.org/all/20250709-sophisticated-loon-of-rain-6ccdd8@houat/
Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
---
 drivers/gpu/drm/drm_bridge.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index 53e7ece36dd940aabd1c0880f296fce7224a12ac..1246a52f8767b52c5f10139aa897824b3c2f28da 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -422,6 +422,9 @@ static bool drm_bridge_is_atomic(struct drm_bridge *bridge)
  * If non-NULL the previous bridge must be already attached by a call to this
  * function.
  *
+ * The bridge to be attached must have been previously added by
+ * drm_bridge_add().
+ *
  * Note that bridges attached to encoders are auto-detached during encoder
  * cleanup in drm_encoder_cleanup(), so drm_bridge_attach() should generally
  * *not* be balanced with a drm_bridge_detach() in driver code.

-- 
2.51.0