of: overlay: Kobjectify overlay objects

We are going to need the overlays to appear on sysfs with runtime
global properties (like master enable) so turn them into kobjects.

They have to be in sysfs so that people can have information about the
overlays applied in the system, i.e. where their targets are and whether
removal is possible. In a future more attributes can be added
in a backwards compatible manner.

Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
[geert: Rebase to v4.15-rc1]
[Fengguang Wu: Make overlay_changeset_release() static]
[geert: Rebase on top of commit 39a751a ("of: change overlay apply input data from unflattened to FDT") in v4.17-rc1]
[geert: Rebase on top of commit 421f4d1 ("of: overlay: do not free changeset when of_overlay_apply returns error") in v5.19-rc1]
[geert: Rebase on top of commit 73aca58 ("of: Move of_platform_register_reconfig_notifier() into DT core") in v6.6-rc1]
[geert: Add kerneldoc for fragment.kobj]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Author: pantoniou

drivers/of/base.c

@@ -166,6 +166,7 @@ void __of_phandle_cache_inv_entry(phandle handle)
 void __init of_core_init(void)
 {
 	struct device_node *np;
+	int ret;
 
 	of_platform_register_reconfig_notifier();
 
@@ -187,6 +188,10 @@ void __init of_core_init(void)
 	/* Symlink in /proc as required by userspace ABI */
 	if (of_root)
 		proc_symlink("device-tree", NULL, "/sys/firmware/devicetree/base");
+
+	ret = of_overlay_init();
+	if (ret != 0)
+		pr_warn("of_init: of_overlay_init failed!\n");
 }
 
 static struct property *__of_find_property(const struct device_node *np,

drivers/of/of_private.h

@@ -182,4 +182,13 @@ void fdt_init_reserved_mem(void);
 void fdt_reserved_mem_save_node(unsigned long node, const char *uname,
 			       phys_addr_t base, phys_addr_t size);
 
+#if defined(CONFIG_OF_OVERLAY)
+extern int of_overlay_init(void);
+#else
+static inline int of_overlay_init(void)
+{
+	return 0;
+}
+#endif
+
 #endif /* _LINUX_OF_PRIVATE_H */

drivers/of/overlay.c

@@ -20,6 +20,7 @@
 #include <linux/libfdt.h>
 #include <linux/err.h>
 #include <linux/idr.h>
+#include <linux/sysfs.h>
 
 #include "of_private.h"
 
@@ -65,6 +66,7 @@ struct fragment {
  * @fragments:		fragment nodes in the overlay expanded device tree
  * @symbols_fragment:	last element of @fragments[] is the  __symbols__ node
  * @cset:		changeset to apply fragments to live device tree
+ * @kobj:		kernel object handle
  */
 struct overlay_changeset {
 	int id;
@@ -77,6 +79,7 @@ struct overlay_changeset {
 	struct fragment *fragments;
 	bool symbols_fragment;
 	struct of_changeset cset;
+	struct kobject kobj;
 };
 
 /* flags are sticky - once set, do not reset */
@@ -868,6 +871,17 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
 		of_node_put(ovcs->fragments[i].overlay);
 	}
 	kfree(ovcs->fragments);
+	kobject_put(&ovcs->kobj);
+}
+
+static inline struct overlay_changeset *kobj_to_ovcs(struct kobject *kobj)
+{
+	return container_of(kobj, struct overlay_changeset, kobj);
+}
+
+static void overlay_changeset_release(struct kobject *kobj)
+{
+	struct overlay_changeset *ovcs = kobj_to_ovcs(kobj);
 
 	/*
 	 * There should be no live pointers into ovcs->overlay_mem and
@@ -887,6 +901,12 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
 	kfree(ovcs);
 }
 
+static struct kobj_type overlay_changeset_ktype = {
+	.release = overlay_changeset_release,
+};
+
+static struct kset *ov_kset;
+
 /*
  * internal documentation
  *
@@ -1015,6 +1035,8 @@ int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
 	if (!ovcs)
 		return -ENOMEM;
 
+	kobject_init(&ovcs->kobj, &overlay_changeset_ktype);
+
 	of_overlay_mutex_lock();
 	mutex_lock(&of_mutex);
 
@@ -1064,6 +1086,16 @@ int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
 	 * can call of_overlay_remove();
 	 */
 	*ret_ovcs_id = ovcs->id;
+
+	if (ret)
+		goto out_unlock;
+
+	ovcs->kobj.kset = ov_kset;
+	ret = kobject_add(&ovcs->kobj, NULL, "%d", ovcs->id);
+	if (ret) {
+		pr_err("%s: kobject_add() failed for tree@%s\n", __func__,
+		       ovcs->overlay_root->full_name);
+	}
 	goto out_unlock;
 
 err_free_ovcs:
@@ -1284,3 +1316,13 @@ int of_overlay_remove_all(void)
 	return 0;
 }
 EXPORT_SYMBOL_GPL(of_overlay_remove_all);
+
+/* called from of_init() */
+int of_overlay_init(void)
+{
+	ov_kset = kset_create_and_add("overlays", NULL, &of_kset->kobj);
+	if (!ov_kset)
+		return -ENOMEM;
+
+	return 0;
+}