path: root/drivers/of/overlay.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Functions for working with device tree overlays
 *
 * Copyright (C) 2012 Pantelis Antoniou <panto@antoniou-consulting.com>
 * Copyright (C) 2012 Texas Instruments Inc.
 */

#define pr_fmt(fmt)	"OF: overlay: " fmt

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/of_device.h>
#include <linux/of_fdt.h>
#include <linux/string.h>
#include <linux/ctype.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/libfdt.h>
#include <linux/err.h>
#include <linux/idr.h>

#include "of_private.h"

/**
 * struct target - info about current target node as recursing through overlay
 * @np:			node where current level of overlay will be applied
 * @in_livetree:	@np is a node in the live devicetree
 *
 * Used in the algorithm to create the portion of a changeset that describes
 * an overlay fragment, which is a devicetree subtree.  Initially @np is a node
 * in the live devicetree where the overlay subtree is targeted to be grafted
 * into.  When recursing to the next level of the overlay subtree, the target
 * also recurses to the next level of the live devicetree, as long as overlay
 * subtree node also exists in the live devicetree.  When a node in the overlay
 * subtree does not exist at the same level in the live devicetree, target->np
 * points to a newly allocated node, and all subsequent targets in the subtree
 * will be newly allocated nodes.
 */
struct target {
	struct device_node *np;
	bool in_livetree;
};

/**
 * struct fragment - info about fragment nodes in overlay expanded device tree
 * @overlay:	pointer to the __overlay__ node
 * @target:	target of the overlay operation
 */
struct fragment {
	struct device_node *overlay;
	struct device_node *target;
};

/**
 * struct overlay_changeset
 * @id:			changeset identifier
 * @ovcs_list:		list on which we are located
 * @new_fdt:		Memory allocated to hold unflattened aligned FDT
 * @overlay_mem:	the memory chunk that contains @overlay_root
 * @overlay_root:	expanded device tree that contains the fragment nodes
 * @notify_state:	most recent notify action used on overlay
 * @count:		count of fragment structures
 * @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
 */
struct overlay_changeset {
	int id;
	struct list_head ovcs_list;
	const void *new_fdt;
	const void *overlay_mem;
	struct device_node *overlay_root;
	enum of_overlay_notify_action notify_state;
	int count;
	struct fragment *fragments;
	bool symbols_fragment;
	struct of_changeset cset;
};

/* flags are sticky - once set, do not reset */
static int devicetree_state_flags;
#define DTSF_APPLY_FAIL		0x01
#define DTSF_REVERT_FAIL	0x02

/*
 * If a changeset apply or revert encounters an error, an attempt will
 * be made to undo partial changes, but may fail.  If the undo fails
 * we do not know the state of the devicetree.
 */
static int devicetree_corrupt(void)
{
	return devicetree_state_flags &
		(DTSF_APPLY_FAIL | DTSF_REVERT_FAIL);
}

static int build_changeset_next_level(struct overlay_changeset *ovcs,
		struct target *target, const struct device_node *overlay_node);

/*
 * of_resolve_phandles() finds the largest phandle in the live tree.
 * of_overlay_apply() may add a larger phandle to the live tree.
 * Do not allow race between two overlays being applied simultaneously:
 *    mutex_lock(&of_overlay_phandle_mutex)
 *    of_resolve_phandles()
 *    of_overlay_apply()
 *    mutex_unlock(&of_overlay_phandle_mutex)
 */
static DEFINE_MUTEX(of_overlay_phandle_mutex);

void of_overlay_mutex_lock(void)
{
	mutex_lock(&of_overlay_phandle_mutex);
}

void of_overlay_mutex_unlock(void)
{
	mutex_unlock(&of_overlay_phandle_mutex);
}

static LIST_HEAD(ovcs_list);
static DEFINE_IDR(ovcs_idr);

static BLOCKING_NOTIFIER_HEAD(overlay_notify_chain);

/**
 * of_overlay_notifier_register() - Register notifier for overlay operations
 * @nb:		Notifier block to register
 *
 * Register for notification on overlay operations on device tree nodes. The
 * reported actions definied by @of_reconfig_change. The notifier callback
 * furthermore receives a pointer to the affected device tree node.
 *
 * Note that a notifier callback is not supposed to store pointers to a device
 * tree node or its content beyond @OF_OVERLAY_POST_REMOVE corresponding to the
 * respective node it received.
 */
int of_overlay_notifier_register(struct notifier_block *nb)
{
	return blocking_notifier_chain_register(&overlay_notify_chain, nb);
}
EXPORT_SYMBOL_GPL(of_overlay_notifier_register);

/**
 * of_overlay_notifier_unregister() - Unregister notifier for overlay operations
 * @nb:		Notifier block to unregister
 */
int of_overlay_notifier_unregister(struct notifier_block *nb)
{
	return blocking_notifier_chain_unregister(&overlay_notify_chain, nb);
}