drm: Plumb debugfs_init through to panels

We'd like panels to be able to add things to debugfs underneath the
connector's directory. Let's plumb it through. A panel will be able to
put things in a "panel" directory under the connector's
directory. Note that debugfs is not ABI and so it's always possible
that the location that the panel gets for its debugfs could change in
the future.

NOTE: this currently only works if you're using a modern
architecture. Specifically the plumbing relies on _both_
drm_bridge_connector and drm_panel_bridge. If you're not using one or
both of these things then things won't be plumbed through.

As a side effect of this change, drm_bridges can also get callbacks to
put stuff underneath the connector's debugfs directory. At the moment
all bridges in the chain have their debugfs_init() called with the
connector's root directory.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220204161245.v2.2.Ib0bd5346135cbb0b63006b69b61d4c8af6484740@changeid

drivers/gpu/drm/bridge/panel.c

@@ -138,6 +138,17 @@ static int panel_bridge_get_modes(struct drm_bridge *bridge,
 	return drm_panel_get_modes(panel_bridge->panel, connector);
 }
 
+static void panel_bridge_debugfs_init(struct drm_bridge *bridge,
+				      struct dentry *root)
+{
+	struct panel_bridge *panel_bridge = drm_bridge_to_panel_bridge(bridge);
+	struct drm_panel *panel = panel_bridge->panel;
+
+	root = debugfs_create_dir("panel", root);
+	if (panel->funcs->debugfs_init)
+		panel->funcs->debugfs_init(panel, root);
+}
+
 static const struct drm_bridge_funcs panel_bridge_bridge_funcs = {
 	.attach = panel_bridge_attach,
 	.detach = panel_bridge_detach,
@@ -150,6 +161,7 @@ static const struct drm_bridge_funcs panel_bridge_bridge_funcs = {
 	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
 	.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
 	.atomic_get_input_bus_fmts = drm_atomic_helper_bridge_propagate_bus_fmt,
+	.debugfs_init = panel_bridge_debugfs_init,
 };
 
 /**

drivers/gpu/drm/drm_bridge_connector.c

@@ -216,6 +216,20 @@ static void drm_bridge_connector_destroy(struct drm_connector *connector)
 	kfree(bridge_connector);
 }
 
+static void drm_bridge_connector_debugfs_init(struct drm_connector *connector,
+					      struct dentry *root)
+{
+	struct drm_bridge_connector *bridge_connector =
+		to_drm_bridge_connector(connector);
+	struct drm_encoder *encoder = bridge_connector->encoder;
+	struct drm_bridge *bridge;
+
+	list_for_each_entry(bridge, &encoder->bridge_chain, chain_node) {
+		if (bridge->funcs->debugfs_init)
+			bridge->funcs->debugfs_init(bridge, root);
+	}
+}
+
 static const struct drm_connector_funcs drm_bridge_connector_funcs = {
 	.reset = drm_atomic_helper_connector_reset,
 	.detect = drm_bridge_connector_detect,
@@ -223,6 +237,7 @@ static const struct drm_connector_funcs drm_bridge_connector_funcs = {
 	.destroy = drm_bridge_connector_destroy,
 	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
 	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
+	.debugfs_init = drm_bridge_connector_debugfs_init,
 };
 
 /* -----------------------------------------------------------------------------

drivers/gpu/drm/drm_debugfs.c

@@ -436,6 +436,9 @@ void drm_debugfs_connector_add(struct drm_connector *connector)
 	/* vrr range */
 	debugfs_create_file("vrr_range", S_IRUGO, root, connector,
 			    &vrr_range_fops);
+
+	if (connector->funcs->debugfs_init)
+		connector->funcs->debugfs_init(connector, root);
 }
 
 void drm_debugfs_connector_remove(struct drm_connector *connector)

include/drm/drm_bridge.h

@@ -649,6 +649,13 @@ struct drm_bridge_funcs {
 	 * the DRM_BRIDGE_OP_HPD flag in their &drm_bridge->ops.
 	 */
 	void (*hpd_disable)(struct drm_bridge *bridge);
+
+	/**
+	 * @debugfs_init:
+	 *
+	 * Allows bridges to create bridge-specific debugfs files.
+	 */
+	void (*debugfs_init)(struct drm_bridge *bridge, struct dentry *root);
 };
 
 /**

include/drm/drm_connector.h

@@ -1142,6 +1142,13 @@ struct drm_connector_funcs {
 	 * has been received from a source outside the display driver / device.
 	 */
 	void (*oob_hotplug_event)(struct drm_connector *connector);
+
+	/**
+	 * @debugfs_init:
+	 *
+	 * Allows connectors to create connector-specific debugfs files.
+	 */
+	void (*debugfs_init)(struct drm_connector *connector, struct dentry *root);
 };
 
 /**

include/drm/drm_panel.h

@@ -29,6 +29,7 @@
 #include <linux/list.h>
 
 struct backlight_device;
+struct dentry;
 struct device_node;
 struct drm_connector;
 struct drm_device;
@@ -125,6 +126,13 @@ struct drm_panel_funcs {
 	 */
 	int (*get_timings)(struct drm_panel *panel, unsigned int num_timings,
 			   struct display_timing *timings);
+
+	/**
+	 * @debugfs_init:
+	 *
+	 * Allows panels to create panels-specific debugfs files.
+	 */
+	void (*debugfs_init)(struct drm_panel *panel, struct dentry *root);
 };
 
 /**