driver core: Add fwnode link support

Add support for creating supplier-consumer links between fwnodes. It is
intended for internal use the driver core and generic firmware support
code (eg. Device Tree, ACPI), so it is simple by design and the API
provided is limited.

Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Saravana Kannan <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/base/core.c

···
 static DEFINE_MUTEX(wfs_lock);
 static LIST_HEAD(deferred_sync);
 static unsigned int defer_sync_state_count = 1;
+static DEFINE_MUTEX(fwnode_link_lock);
+
+/**
+ * fwnode_link_add - Create a link between two fwnode_handles.
+ * @con: Consumer end of the link.
+ * @sup: Supplier end of the link.
+ *
+ * Create a fwnode link between fwnode handles @con and @sup. The fwnode link
+ * represents the detail that the firmware lists @sup fwnode as supplying a
+ * resource to @con.
+ *
+ * The driver core will use the fwnode link to create a device link between the
+ * two device objects corresponding to @con and @sup when they are created. The
+ * driver core will automatically delete the fwnode link between @con and @sup
+ * after doing that.
+ *
+ * Attempts to create duplicate links between the same pair of fwnode handles
+ * are ignored and there is no reference counting.
+ */
+int fwnode_link_add(struct fwnode_handle *con, struct fwnode_handle *sup)
+{
+	struct fwnode_link *link;
+	int ret = 0;
+
+	mutex_lock(&fwnode_link_lock);
+
+	list_for_each_entry(link, &sup->consumers, s_hook)
+		if (link->consumer == con)
+			goto out;
+
+	link = kzalloc(sizeof(*link), GFP_KERNEL);
+	if (!link) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	link->supplier = sup;
+	INIT_LIST_HEAD(&link->s_hook);
+	link->consumer = con;
+	INIT_LIST_HEAD(&link->c_hook);
+
+	list_add(&link->s_hook, &sup->consumers);
+	list_add(&link->c_hook, &con->suppliers);
+out:
+	mutex_unlock(&fwnode_link_lock);
+
+	return ret;
+}
+
+/**
+ * fwnode_links_purge_suppliers - Delete all supplier links of fwnode_handle.
+ * @fwnode: fwnode whose supplier links need to be deleted
+ *
+ * Deletes all supplier links connecting directly to @fwnode.
+ */
+static void fwnode_links_purge_suppliers(struct fwnode_handle *fwnode)
+{
+	struct fwnode_link *link, *tmp;
+
+	mutex_lock(&fwnode_link_lock);
+	list_for_each_entry_safe(link, tmp, &fwnode->suppliers, c_hook) {
+		list_del(&link->s_hook);
+		list_del(&link->c_hook);
+		kfree(link);
+	}
+	mutex_unlock(&fwnode_link_lock);
+}
+
+/**
+ * fwnode_links_purge_consumers - Delete all consumer links of fwnode_handle.
+ * @fwnode: fwnode whose consumer links need to be deleted
+ *
+ * Deletes all consumer links connecting directly to @fwnode.
+ */
+static void fwnode_links_purge_consumers(struct fwnode_handle *fwnode)
+{
+	struct fwnode_link *link, *tmp;
+
+	mutex_lock(&fwnode_link_lock);
+	list_for_each_entry_safe(link, tmp, &fwnode->consumers, s_hook) {
+		list_del(&link->s_hook);
+		list_del(&link->c_hook);
+		kfree(link);
+	}
+	mutex_unlock(&fwnode_link_lock);
+}
+
+/**
+ * fwnode_links_purge - Delete all links connected to a fwnode_handle.
+ * @fwnode: fwnode whose links needs to be deleted
+ *
+ * Deletes all links connecting directly to a fwnode.
+ */
+void fwnode_links_purge(struct fwnode_handle *fwnode)
+{
+	fwnode_links_purge_suppliers(fwnode);
+	fwnode_links_purge_consumers(fwnode);
+}
 
 #ifdef CONFIG_SRCU
 static DEFINE_MUTEX(device_links_lock);

drivers/of/dynamic.c

···
 
 	property_list_free(node->properties);
 	property_list_free(node->deadprops);
+	fwnode_links_purge(of_fwnode_handle(node));
 
 	kfree(node->full_name);
 	kfree(node->data);

include/linux/fwnode.h

···
 #define _LINUX_FWNODE_H_
 
 #include <linux/types.h>
+#include <linux/list.h>
 
 struct fwnode_operations;
 struct device;
···
 	struct fwnode_handle *secondary;
 	const struct fwnode_operations *ops;
 	struct device *dev;
+	struct list_head suppliers;
+	struct list_head consumers;
+};
+
+struct fwnode_link {
+	struct fwnode_handle *supplier;
+	struct list_head s_hook;
+	struct fwnode_handle *consumer;
+	struct list_head c_hook;
 };
 
 /**
···
 			       const struct fwnode_operations *ops)
 {
 	fwnode->ops = ops;
+	INIT_LIST_HEAD(&fwnode->consumers);
+	INIT_LIST_HEAD(&fwnode->suppliers);
 }
 
 extern u32 fw_devlink_get_flags(void);
+int fwnode_link_add(struct fwnode_handle *con, struct fwnode_handle *sup);
+void fwnode_links_purge(struct fwnode_handle *fwnode);
 
 #endif