drm/bridge: add devm_drm_bridge_alloc()

Add a macro to allocate and initialize a DRM bridge embedded within a
private driver struct.

Compared to current practice, which is based on [devm_]kzalloc() allocation
followed by open-coded initialization of fields, this allows to have a
common and explicit API to allocate and initialize DRM bridges.

Besides being useful to consolidate bridge driver code, this is a
fundamental step in preparation for adding dynamic lifetime to bridges
based on refcount.

Reviewed-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250326-drm-bridge-refcount-v9-1-5e0661fe1f84@bootlin.com
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>

drivers/gpu/drm/drm_bridge.c

@@ -199,6 +199,28 @@
 static DEFINE_MUTEX(bridge_lock);
 static LIST_HEAD(bridge_list);
 
+void *__devm_drm_bridge_alloc(struct device *dev, size_t size, size_t offset,
+			      const struct drm_bridge_funcs *funcs)
+{
+	void *container;
+	struct drm_bridge *bridge;
+
+	if (!funcs) {
+		dev_warn(dev, "Missing funcs pointer\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	container = devm_kzalloc(dev, size, GFP_KERNEL);
+	if (!container)
+		return ERR_PTR(-ENOMEM);
+
+	bridge = container + offset;
+	bridge->funcs = funcs;
+
+	return container;
+}
+EXPORT_SYMBOL(__devm_drm_bridge_alloc);
+
 /**
  * drm_bridge_add - add the given bridge to the global bridge list
  *

include/drm/drm_bridge.h

@@ -941,6 +941,23 @@ drm_priv_to_bridge(struct drm_private_obj *priv)
 	return container_of(priv, struct drm_bridge, base);
 }
 
+void *__devm_drm_bridge_alloc(struct device *dev, size_t size, size_t offset,
+			      const struct drm_bridge_funcs *funcs);
+
+/**
+ * devm_drm_bridge_alloc - Allocate and initialize a bridge
+ * @dev: struct device of the bridge device
+ * @type: the type of the struct which contains struct &drm_bridge
+ * @member: the name of the &drm_bridge within @type
+ * @funcs: callbacks for this bridge
+ *
+ * Returns:
+ * Pointer to new bridge, or ERR_PTR on failure.
+ */
+#define devm_drm_bridge_alloc(dev, type, member, funcs) \
+	((type *)__devm_drm_bridge_alloc(dev, sizeof(type), \
+					 offsetof(type, member), funcs))
+
 void drm_bridge_add(struct drm_bridge *bridge);
 int devm_drm_bridge_add(struct device *dev, struct drm_bridge *bridge);
 void drm_bridge_remove(struct drm_bridge *bridge);