linux-kernel - [PATCH v6 12/26] drm/bridge: allow bridges to be informed about added and removed bridges

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Message-Id: <20250206-hotplug-drm-bridge-v6-12-9d6f2c9c3058@bootlin.com>
Date: Thu, 06 Feb 2025 19:14:27 +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 12/26] drm/bridge: allow bridges to be informed about
 added and removed bridges

In preparation for allowing bridges to be added to and removed from a DRM
card without destroying the whole card, add a new DRM bridge function
called on addition and removal of bridges.

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

---

Changed in v6:
 - rebased fixing conflicts

Changed in v5:
 - fixed kerneldoc errors

This patch was added in v4.
---
 drivers/gpu/drm/drm_bridge.c | 12 ++++++++++++
 include/drm/drm_bridge.h     | 23 +++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
index b0834b8644284e5f7751cec81724af849b4180e7..1955a231378050abf1071d74a145831b425c47c5 100644
--- a/drivers/gpu/drm/drm_bridge.c
+++ b/drivers/gpu/drm/drm_bridge.c
@@ -207,12 +207,18 @@ LIST_HEAD(bridge_list);
  */
 void drm_bridge_add(struct drm_bridge *bridge)
 {
+	struct drm_bridge *br, *tmp;
+
 	mutex_init(&bridge->hpd_mutex);
 
 	if (bridge->ops & DRM_BRIDGE_OP_HDMI)
 		bridge->ycbcr_420_allowed = !!(bridge->supported_formats &
 					       BIT(HDMI_COLORSPACE_YUV420));
 
+	list_for_each_entry_safe(br, tmp, &bridge_list, list)
+		if (br->funcs->bridge_event_notify)
+			br->funcs->bridge_event_notify(br, DRM_EVENT_BRIDGE_ADD, bridge);
+
 	mutex_lock(&bridge_lock);
 	list_add_tail(&bridge->list, &bridge_list);
 	mutex_unlock(&bridge_lock);
@@ -249,10 +255,16 @@ EXPORT_SYMBOL(devm_drm_bridge_add);
  */
 void drm_bridge_remove(struct drm_bridge *bridge)
 {
+	struct drm_bridge *br, *tmp;
+
 	mutex_lock(&bridge_lock);
 	list_del_init(&bridge->list);
 	mutex_unlock(&bridge_lock);
 
+	list_for_each_entry_safe(br, tmp, &bridge_list, list)
+		if (br->funcs->bridge_event_notify)
+			br->funcs->bridge_event_notify(br, DRM_EVENT_BRIDGE_REMOVE, bridge);
+
 	mutex_destroy(&bridge->hpd_mutex);
 }
 EXPORT_SYMBOL(drm_bridge_remove);
diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
index 1561347c4991dac6022319774510f9560c9283c3..ad7ba444a13e5ecf16f996de3742e4ac67dc21f1 100644
--- a/include/drm/drm_bridge.h
+++ b/include/drm/drm_bridge.h
@@ -56,6 +56,11 @@ enum drm_bridge_attach_flags {
 	DRM_BRIDGE_ATTACH_NO_CONNECTOR = BIT(0),
 };
 
+enum drm_bridge_event_type {
+	DRM_EVENT_BRIDGE_ADD,
+	DRM_EVENT_BRIDGE_REMOVE,
+};
+
 /**
  * struct drm_bridge_funcs - drm_bridge control functions
  */
@@ -729,6 +734,24 @@ struct drm_bridge_funcs {
 				      struct drm_bridge *bridge,
 				      bool enable, int direction);
 
+	/**
+	 * @bridge_event_notify:
+	 *
+	 * Notify that another bridge is being added or removed.
+	 *
+	 * This callback is optional. Bridges implementing it must always
+	 * check whether the event refers to a bridge they actually need to
+	 * interact with.
+	 *
+	 * @bridge: bridge being notified
+	 * @event: event happened (add/remove bridge)
+	 * @event_bridge: the bridge mentioned by the event (i.e. the
+	 * bridge being added or removed)
+	 */
+	void (*bridge_event_notify)(struct drm_bridge *bridge,
+				    enum drm_bridge_event_type event,
+				    struct drm_bridge *event_bridge);
+
 	/**
 	 * @debugfs_init:
 	 *

-- 
2.34.1