USB: serial: option: add support for Telit ME910 PID 0x1101

[linux/fpc-iii.git] / drivers / of / overlay.c

/*
 * Functions for working with device tree overlays
 *
 * Copyright (C) 2012 Pantelis Antoniou <panto@antoniou-consulting.com>
 * Copyright (C) 2012 Texas Instruments Inc.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * version 2 as published by the Free Software Foundation.
 */

#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/string.h>
#include <linux/ctype.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/idr.h>

#include "of_private.h"

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

/**
 * struct overlay_changeset
 * @ovcs_list:          list on which we are located
 * @overlay_tree:       expanded device tree that contains the fragment nodes
 * @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;
        struct device_node *overlay_tree;
        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 device_node *target_node,
                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);

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);

int of_overlay_notifier_unregister(struct notifier_block *nb)
{
        return blocking_notifier_chain_unregister(&overlay_notify_chain, nb);
}
EXPORT_SYMBOL_GPL(of_overlay_notifier_unregister);

static char *of_overlay_action_name[] = {
        "pre-apply",
        "post-apply",
        "pre-remove",
        "post-remove",
};

static int overlay_notify(struct overlay_changeset *ovcs,
                enum of_overlay_notify_action action)
{
        struct of_overlay_notify_data nd;
        int i, ret;

        for (i = 0; i < ovcs->count; i++) {
                struct fragment *fragment = &ovcs->fragments[i];

                nd.target = fragment->target;
                nd.overlay = fragment->overlay;

                ret = blocking_notifier_call_chain(&overlay_notify_chain,
                                                   action, &nd);
                if (ret == NOTIFY_OK || ret == NOTIFY_STOP)
                        return 0;
                if (ret) {
                        ret = notifier_to_errno(ret);
                        pr_err("overlay changeset %s notifier error %d, target: %pOF\n",
                               of_overlay_action_name[action], ret, nd.target);
                        return ret;
                }
        }

        return 0;
}

/*
 * The values of properties in the "/__symbols__" node are paths in
 * the ovcs->overlay_tree.  When duplicating the properties, the paths
 * need to be adjusted to be the correct path for the live device tree.
 *
 * The paths refer to a node in the subtree of a fragment node's "__overlay__"
 * node, for example "/fragment@0/__overlay__/symbol_path_tail",
 * where symbol_path_tail can be a single node or it may be a multi-node path.
 *
 * The duplicated property value will be modified by replacing the
 * "/fragment_name/__overlay/" portion of the value  with the target
 * path from the fragment node.
 */
static struct property *dup_and_fixup_symbol_prop(
                struct overlay_changeset *ovcs, const struct property *prop)
{
        struct fragment *fragment;
        struct property *new_prop;
        struct device_node *fragment_node;
        struct device_node *overlay_node;
        const char *path;
        const char *path_tail;
        const char *target_path;
        int k;
        int overlay_name_len;
        int path_len;
        int path_tail_len;
        int target_path_len;

        if (!prop->value)
                return NULL;
        if (strnlen(prop->value, prop->length) >= prop->length)
                return NULL;
        path = prop->value;
        path_len = strlen(path);

        if (path_len < 1)
                return NULL;
        fragment_node = __of_find_node_by_path(ovcs->overlay_tree, path + 1);
        overlay_node = __of_find_node_by_path(fragment_node, "__overlay__/");
        of_node_put(fragment_node);
        of_node_put(overlay_node);

        for (k = 0; k < ovcs->count; k++) {
                fragment = &ovcs->fragments[k];
                if (fragment->overlay == overlay_node)
                        break;
        }
        if (k >= ovcs->count)
                return NULL;

        overlay_name_len = snprintf(NULL, 0, "%pOF", fragment->overlay);

        if (overlay_name_len > path_len)
                return NULL;
        path_tail = path + overlay_name_len;
        path_tail_len = strlen(path_tail);

        target_path = kasprintf(GFP_KERNEL, "%pOF", fragment->target);
        if (!target_path)
                return NULL;
        target_path_len = strlen(target_path);

        new_prop = kzalloc(sizeof(*new_prop), GFP_KERNEL);
        if (!new_prop)
                goto err_free_target_path;

        new_prop->name = kstrdup(prop->name, GFP_KERNEL);
        new_prop->length = target_path_len + path_tail_len + 1;
        new_prop->value = kzalloc(new_prop->length, GFP_KERNEL);
        if (!new_prop->name || !new_prop->value)
                goto err_free_new_prop;

        strcpy(new_prop->value, target_path);
        strcpy(new_prop->value + target_path_len, path_tail);

        of_property_set_flag(new_prop, OF_DYNAMIC);

        return new_prop;

err_free_new_prop:
        kfree(new_prop->name);
        kfree(new_prop->value);
        kfree(new_prop);
err_free_target_path:
        kfree(target_path);

        return NULL;
}

/**
 * add_changeset_property() - add @overlay_prop to overlay changeset
 * @ovcs:               overlay changeset
 * @target_node:        where to place @overlay_prop in live tree
 * @overlay_prop:       property to add or update, from overlay tree
 * @is_symbols_prop:    1 if @overlay_prop is from node "/__symbols__"
 *
 * If @overlay_prop does not already exist in @target_node, add changeset entry
 * to add @overlay_prop in @target_node, else add changeset entry to update
 * value of @overlay_prop.
 *
 * Some special properties are not updated (no error returned).
 *
 * Update of property in symbols node is not allowed.
 *
 * Returns 0 on success, -ENOMEM if memory allocation failure, or -EINVAL if
 * invalid @overlay.
 */
static int add_changeset_property(struct overlay_changeset *ovcs,
                struct device_node *target_node,
                struct property *overlay_prop,
                bool is_symbols_prop)
{
        struct property *new_prop = NULL, *prop;
        int ret = 0;

        prop = of_find_property(target_node, overlay_prop->name, NULL);

        if (!of_prop_cmp(overlay_prop->name, "name") ||
            !of_prop_cmp(overlay_prop->name, "phandle") ||
            !of_prop_cmp(overlay_prop->name, "linux,phandle"))
                return 0;

        if (is_symbols_prop) {
                if (prop)
                        return -EINVAL;
                new_prop = dup_and_fixup_symbol_prop(ovcs, overlay_prop);
        } else {
                new_prop = __of_prop_dup(overlay_prop, GFP_KERNEL);
        }

        if (!new_prop)
                return -ENOMEM;

        if (!prop)
                ret = of_changeset_add_property(&ovcs->cset, target_node,
                                                new_prop);
        else
                ret = of_changeset_update_property(&ovcs->cset, target_node,
                                                   new_prop);

        if (ret) {
                kfree(new_prop->name);
                kfree(new_prop->value);
                kfree(new_prop);
        }
        return ret;
}

/**
 * add_changeset_node() - add @node (and children) to overlay changeset
 * @ovcs:               overlay changeset
 * @target_node:        where to place @node in live tree
 * @node:               node from within overlay device tree fragment
 *
 * If @node does not already exist in @target_node, add changeset entry
 * to add @node in @target_node.
 *
 * If @node already exists in @target_node, and the existing node has
 * a phandle, the overlay node is not allowed to have a phandle.
 *
 * If @node has child nodes, add the children recursively via
 * build_changeset_next_level().
 *
 * NOTE: Multiple mods of created nodes not supported.
 *       If more than one fragment contains a node that does not already exist
 *       in the live tree, then for each fragment of_changeset_attach_node()
 *       will add a changeset entry to add the node.  When the changeset is
 *       applied, __of_attach_node() will attach the node twice (once for
 *       each fragment).  At this point the device tree will be corrupted.
 *
 *       TODO: add integrity check to ensure that multiple fragments do not
 *             create the same node.
 *
 * Returns 0 on success, -ENOMEM if memory allocation failure, or -EINVAL if
 * invalid @overlay.
 */
static int add_changeset_node(struct overlay_changeset *ovcs,
                struct device_node *target_node, struct device_node *node)
{
        const char *node_kbasename;
        struct device_node *tchild;
        int ret = 0;

        node_kbasename = kbasename(node->full_name);

        for_each_child_of_node(target_node, tchild)
                if (!of_node_cmp(node_kbasename, kbasename(tchild->full_name)))
                        break;

        if (!tchild) {
                tchild = __of_node_dup(node, "%pOF/%s",
                                       target_node, node_kbasename);
                if (!tchild)
                        return -ENOMEM;

                tchild->parent = target_node;

                ret = of_changeset_attach_node(&ovcs->cset, tchild);
                if (ret)
                        return ret;

                return build_changeset_next_level(ovcs, tchild, node);
        }

        if (node->phandle && tchild->phandle)
                ret = -EINVAL;
        else
                ret = build_changeset_next_level(ovcs, tchild, node);
        of_node_put(tchild);

        return ret;
}

/**
 * build_changeset_next_level() - add level of overlay changeset
 * @ovcs:               overlay changeset
 * @target_node:        where to place @overlay_node in live tree
 * @overlay_node:       node from within an overlay device tree fragment
 *
 * Add the properties (if any) and nodes (if any) from @overlay_node to the
 * @ovcs->cset changeset.  If an added node has child nodes, they will
 * be added recursively.
 *
 * Do not allow symbols node to have any children.
 *
 * Returns 0 on success, -ENOMEM if memory allocation failure, or -EINVAL if
 * invalid @overlay_node.
 */
static int build_changeset_next_level(struct overlay_changeset *ovcs,
                struct device_node *target_node,
                const struct device_node *overlay_node)
{
        struct device_node *child;
        struct property *prop;
        int ret;

        for_each_property_of_node(overlay_node, prop) {
                ret = add_changeset_property(ovcs, target_node, prop, 0);
                if (ret) {
                        pr_debug("Failed to apply prop @%pOF/%s, err=%d\n",
                                 target_node, prop->name, ret);
                        return ret;
                }
        }

        for_each_child_of_node(overlay_node, child) {
                ret = add_changeset_node(ovcs, target_node, child);
                if (ret) {
                        pr_debug("Failed to apply node @%pOF/%s, err=%d\n",
                                 target_node, child->name, ret);
                        of_node_put(child);
                        return ret;
                }
        }

        return 0;
}

/*
 * Add the properties from __overlay__ node to the @ovcs->cset changeset.
 */
static int build_changeset_symbols_node(struct overlay_changeset *ovcs,
                struct device_node *target_node,
                const struct device_node *overlay_symbols_node)
{
        struct property *prop;
        int ret;

        for_each_property_of_node(overlay_symbols_node, prop) {
                ret = add_changeset_property(ovcs, target_node, prop, 1);
                if (ret) {
                        pr_debug("Failed to apply prop @%pOF/%s, err=%d\n",
                                 target_node, prop->name, ret);
                        return ret;
                }
        }

        return 0;
}

/**
 * build_changeset() - populate overlay changeset in @ovcs from @ovcs->fragments
 * @ovcs:       Overlay changeset
 *
 * Create changeset @ovcs->cset to contain the nodes and properties of the
 * overlay device tree fragments in @ovcs->fragments[].  If an error occurs,
 * any portions of the changeset that were successfully created will remain
 * in @ovcs->cset.
 *
 * Returns 0 on success, -ENOMEM if memory allocation failure, or -EINVAL if
 * invalid overlay in @ovcs->fragments[].
 */
static int build_changeset(struct overlay_changeset *ovcs)
{
        struct fragment *fragment;
        int fragments_count, i, ret;

        /*
         * if there is a symbols fragment in ovcs->fragments[i] it is
         * the final element in the array
         */
        if (ovcs->symbols_fragment)
                fragments_count = ovcs->count - 1;
        else
                fragments_count = ovcs->count;

        for (i = 0; i < fragments_count; i++) {
                fragment = &ovcs->fragments[i];

                ret = build_changeset_next_level(ovcs, fragment->target,
                                                 fragment->overlay);
                if (ret) {
                        pr_debug("apply failed '%pOF'\n", fragment->target);
                        return ret;
                }
        }

        if (ovcs->symbols_fragment) {
                fragment = &ovcs->fragments[ovcs->count - 1];
                ret = build_changeset_symbols_node(ovcs, fragment->target,
                                                   fragment->overlay);
                if (ret) {
                        pr_debug("apply failed '%pOF'\n", fragment->target);
                        return ret;
                }
        }

        return 0;
}

/*
 * Find the target node using a number of different strategies
 * in order of preference:
 *
 * 1) "target" property containing the phandle of the target
 * 2) "target-path" property containing the path of the target
 */
static struct device_node *find_target_node(struct device_node *info_node)
{
        const char *path;
        u32 val;
        int ret;

        ret = of_property_read_u32(info_node, "target", &val);
        if (!ret)
                return of_find_node_by_phandle(val);

        ret = of_property_read_string(info_node, "target-path", &path);
        if (!ret)
                return of_find_node_by_path(path);

        pr_err("Failed to find target for node %p (%s)\n",
                info_node, info_node->name);

        return NULL;
}

/**
 * init_overlay_changeset() - initialize overlay changeset from overlay tree
 * @ovcs        Overlay changeset to build
 * @tree:       Contains all the overlay fragments and overlay fixup nodes
 *
 * Initialize @ovcs.  Populate @ovcs->fragments with node information from
 * the top level of @tree.  The relevant top level nodes are the fragment
 * nodes and the __symbols__ node.  Any other top level node will be ignored.
 *
 * Returns 0 on success, -ENOMEM if memory allocation failure, -EINVAL if error
 * detected in @tree, or -ENOSPC if idr_alloc() error.
 */
static int init_overlay_changeset(struct overlay_changeset *ovcs,
                struct device_node *tree)
{
        struct device_node *node, *overlay_node;
        struct fragment *fragment;
        struct fragment *fragments;
        int cnt, id, ret;

        /*
         * Warn for some issues.  Can not return -EINVAL for these until
         * of_unittest_apply_overlay() is fixed to pass these checks.
         */
        if (!of_node_check_flag(tree, OF_DYNAMIC))
                pr_debug("%s() tree is not dynamic\n", __func__);

        if (!of_node_check_flag(tree, OF_DETACHED))
                pr_debug("%s() tree is not detached\n", __func__);

        if (!of_node_is_root(tree))
                pr_debug("%s() tree is not root\n", __func__);

        ovcs->overlay_tree = tree;

        INIT_LIST_HEAD(&ovcs->ovcs_list);

        of_changeset_init(&ovcs->cset);

        id = idr_alloc(&ovcs_idr, ovcs, 1, 0, GFP_KERNEL);
        if (id <= 0)
                return id;

        cnt = 0;

        /* fragment nodes */
        for_each_child_of_node(tree, node) {
                overlay_node = of_get_child_by_name(node, "__overlay__");
                if (overlay_node) {
                        cnt++;
                        of_node_put(overlay_node);
                }
        }

        node = of_get_child_by_name(tree, "__symbols__");
        if (node) {
                cnt++;
                of_node_put(node);
        }

        fragments = kcalloc(cnt, sizeof(*fragments), GFP_KERNEL);
        if (!fragments) {
                ret = -ENOMEM;
                goto err_free_idr;
        }

        cnt = 0;
        for_each_child_of_node(tree, node) {
                overlay_node = of_get_child_by_name(node, "__overlay__");
                if (!overlay_node)
                        continue;

                fragment = &fragments[cnt];
                fragment->overlay = overlay_node;
                fragment->target = find_target_node(node);
                if (!fragment->target) {
                        of_node_put(fragment->overlay);
                        ret = -EINVAL;
                        goto err_free_fragments;
                }

                cnt++;
        }

        /*
         * if there is a symbols fragment in ovcs->fragments[i] it is
         * the final element in the array
         */
        node = of_get_child_by_name(tree, "__symbols__");
        if (node) {
                ovcs->symbols_fragment = 1;
                fragment = &fragments[cnt];
                fragment->overlay = node;
                fragment->target = of_find_node_by_path("/__symbols__");

                if (!fragment->target) {
                        pr_err("symbols in overlay, but not in live tree\n");
                        ret = -EINVAL;
                        goto err_free_fragments;
                }

                cnt++;
        }

        if (!cnt) {
                ret = -EINVAL;
                goto err_free_fragments;
        }

        ovcs->id = id;
        ovcs->count = cnt;
        ovcs->fragments = fragments;

        return 0;

err_free_fragments:
        kfree(fragments);
err_free_idr:
        idr_remove(&ovcs_idr, id);

        pr_err("%s() failed, ret = %d\n", __func__, ret);

        return ret;
}

static void free_overlay_changeset(struct overlay_changeset *ovcs)
{
        int i;

        if (ovcs->cset.entries.next)
                of_changeset_destroy(&ovcs->cset);

        if (ovcs->id)
                idr_remove(&ovcs_idr, ovcs->id);

        for (i = 0; i < ovcs->count; i++) {
                of_node_put(ovcs->fragments[i].target);
                of_node_put(ovcs->fragments[i].overlay);
        }
        kfree(ovcs->fragments);

        kfree(ovcs);
}

/**
 * of_overlay_apply() - Create and apply an overlay changeset
 * @tree:       Expanded overlay device tree
 * @ovcs_id:    Pointer to overlay changeset id
 *
 * Creates and applies an overlay changeset.
 *
 * If an error occurs in a pre-apply notifier, then no changes are made
 * to the device tree.
 *

 * A non-zero return value will not have created the changeset if error is from:
 *   - parameter checks
 *   - building the changeset
 *   - overlay changeset pre-apply notifier
 *
 * If an error is returned by an overlay changeset pre-apply notifier
 * then no further overlay changeset pre-apply notifier will be called.
 *
 * A non-zero return value will have created the changeset if error is from:
 *   - overlay changeset entry notifier
 *   - overlay changeset post-apply notifier
 *
 * If an error is returned by an overlay changeset post-apply notifier
 * then no further overlay changeset post-apply notifier will be called.
 *
 * If more than one notifier returns an error, then the last notifier
 * error to occur is returned.
 *
 * If an error occurred while applying the overlay changeset, then an
 * attempt is made to revert any changes that were made to the
 * device tree.  If there were any errors during the revert attempt
 * then the state of the device tree can not be determined, and any
 * following attempt to apply or remove an overlay changeset will be
 * refused.
 *
 * Returns 0 on success, or a negative error number.  Overlay changeset
 * id is returned to *ovcs_id.
 */

int of_overlay_apply(struct device_node *tree, int *ovcs_id)
{
        struct overlay_changeset *ovcs;
        int ret = 0, ret_revert, ret_tmp;

        *ovcs_id = 0;

        if (devicetree_corrupt()) {
                pr_err("devicetree state suspect, refuse to apply overlay\n");
                ret = -EBUSY;
                goto out;
        }

        ovcs = kzalloc(sizeof(*ovcs), GFP_KERNEL);
        if (!ovcs) {
                ret = -ENOMEM;
                goto out;
        }

        of_overlay_mutex_lock();
        mutex_lock(&of_mutex);

        ret = of_resolve_phandles(tree);
        if (ret)
                goto err_free_overlay_changeset;

        ret = init_overlay_changeset(ovcs, tree);
        if (ret)
                goto err_free_overlay_changeset;

        ret = overlay_notify(ovcs, OF_OVERLAY_PRE_APPLY);
        if (ret) {
                pr_err("overlay changeset pre-apply notify error %d\n", ret);
                goto err_free_overlay_changeset;
        }

        ret = build_changeset(ovcs);
        if (ret)
                goto err_free_overlay_changeset;

        ret_revert = 0;
        ret = __of_changeset_apply_entries(&ovcs->cset, &ret_revert);
        if (ret) {
                if (ret_revert) {
                        pr_debug("overlay changeset revert error %d\n",
                                 ret_revert);
                        devicetree_state_flags |= DTSF_APPLY_FAIL;
                }
                goto err_free_overlay_changeset;
        }

        ret = __of_changeset_apply_notify(&ovcs->cset);
        if (ret)
                pr_err("overlay changeset entry notify error %d\n", ret);
        /* notify failure is not fatal, continue */

        list_add_tail(&ovcs->ovcs_list, &ovcs_list);
        *ovcs_id = ovcs->id;

        ret_tmp = overlay_notify(ovcs, OF_OVERLAY_POST_APPLY);
        if (ret_tmp) {
                pr_err("overlay changeset post-apply notify error %d\n",
                       ret_tmp);
                if (!ret)
                        ret = ret_tmp;
        }

        goto out_unlock;

err_free_overlay_changeset:
        free_overlay_changeset(ovcs);

out_unlock:
        mutex_unlock(&of_mutex);
        of_overlay_mutex_unlock();

out:
        pr_debug("%s() err=%d\n", __func__, ret);

        return ret;
}
EXPORT_SYMBOL_GPL(of_overlay_apply);

/*
 * Find @np in @tree.
 *
 * Returns 1 if @np is @tree or is contained in @tree, else 0
 */
static int find_node(struct device_node *tree, struct device_node *np)
{
        struct device_node *child;

        if (tree == np)
                return 1;

        for_each_child_of_node(tree, child) {
                if (find_node(child, np)) {
                        of_node_put(child);
                        return 1;
                }
        }

        return 0;
}

/*
 * Is @remove_ce_node a child of, a parent of, or the same as any
 * node in an overlay changeset more topmost than @remove_ovcs?
 *
 * Returns 1 if found, else 0
 */
static int node_overlaps_later_cs(struct overlay_changeset *remove_ovcs,
                struct device_node *remove_ce_node)
{
        struct overlay_changeset *ovcs;
        struct of_changeset_entry *ce;

        list_for_each_entry_reverse(ovcs, &ovcs_list, ovcs_list) {
                if (ovcs == remove_ovcs)
                        break;

                list_for_each_entry(ce, &ovcs->cset.entries, node) {
                        if (find_node(ce->np, remove_ce_node)) {
                                pr_err("%s: #%d overlaps with #%d @%pOF\n",
                                        __func__, remove_ovcs->id, ovcs->id,
                                        remove_ce_node);
                                return 1;
                        }
                        if (find_node(remove_ce_node, ce->np)) {
                                pr_err("%s: #%d overlaps with #%d @%pOF\n",
                                        __func__, remove_ovcs->id, ovcs->id,
                                        remove_ce_node);
                                return 1;
                        }
                }
        }

        return 0;
}

/*
 * We can safely remove the overlay only if it's the top-most one.
 * Newly applied overlays are inserted at the tail of the overlay list,
 * so a top most overlay is the one that is closest to the tail.
 *
 * The topmost check is done by exploiting this property. For each
 * affected device node in the log list we check if this overlay is
 * the one closest to the tail. If another overlay has affected this
 * device node and is closest to the tail, then removal is not permited.
 */
static int overlay_removal_is_ok(struct overlay_changeset *remove_ovcs)
{
        struct of_changeset_entry *remove_ce;

        list_for_each_entry(remove_ce, &remove_ovcs->cset.entries, node) {
                if (node_overlaps_later_cs(remove_ovcs, remove_ce->np)) {
                        pr_err("overlay #%d is not topmost\n", remove_ovcs->id);
                        return 0;
                }
        }

        return 1;
}

/**
 * of_overlay_remove() - Revert and free an overlay changeset
 * @ovcs_id:    Pointer to overlay changeset id
 *
 * Removes an overlay if it is permissible.  @ovcs_id was previously returned
 * by of_overlay_apply().
 *
 * If an error occurred while attempting to revert the overlay changeset,
 * then an attempt is made to re-apply any changeset entry that was
 * reverted.  If an error occurs on re-apply then the state of the device
 * tree can not be determined, and any following attempt to apply or remove
 * an overlay changeset will be refused.
 *
 * A non-zero return value will not revert the changeset if error is from:
 *   - parameter checks
 *   - overlay changeset pre-remove notifier
 *   - overlay changeset entry revert
 *
 * If an error is returned by an overlay changeset pre-remove notifier
 * then no further overlay changeset pre-remove notifier will be called.
 *
 * If more than one notifier returns an error, then the last notifier
 * error to occur is returned.
 *
 * A non-zero return value will revert the changeset if error is from:
 *   - overlay changeset entry notifier
 *   - overlay changeset post-remove notifier
 *
 * If an error is returned by an overlay changeset post-remove notifier
 * then no further overlay changeset post-remove notifier will be called.
 *
 * Returns 0 on success, or a negative error number.  *ovcs_id is set to
 * zero after reverting the changeset, even if a subsequent error occurs.
 */
int of_overlay_remove(int *ovcs_id)
{
        struct overlay_changeset *ovcs;
        int ret, ret_apply, ret_tmp;

        ret = 0;

        if (devicetree_corrupt()) {
                pr_err("suspect devicetree state, refuse to remove overlay\n");
                ret = -EBUSY;
                goto out;
        }

        mutex_lock(&of_mutex);

        ovcs = idr_find(&ovcs_idr, *ovcs_id);
        if (!ovcs) {
                ret = -ENODEV;
                pr_err("remove: Could not find overlay #%d\n", *ovcs_id);
                goto out_unlock;
        }

        if (!overlay_removal_is_ok(ovcs)) {
                ret = -EBUSY;
                goto out_unlock;
        }

        ret = overlay_notify(ovcs, OF_OVERLAY_PRE_REMOVE);
        if (ret) {
                pr_err("overlay changeset pre-remove notify error %d\n", ret);
                goto out_unlock;
        }

        list_del(&ovcs->ovcs_list);

        ret_apply = 0;
        ret = __of_changeset_revert_entries(&ovcs->cset, &ret_apply);
        if (ret) {
                if (ret_apply)
                        devicetree_state_flags |= DTSF_REVERT_FAIL;
                goto out_unlock;
        }

        ret = __of_changeset_revert_notify(&ovcs->cset);
        if (ret)
                pr_err("overlay changeset entry notify error %d\n", ret);
        /* notify failure is not fatal, continue */

        *ovcs_id = 0;

        ret_tmp = overlay_notify(ovcs, OF_OVERLAY_POST_REMOVE);
        if (ret_tmp) {
                pr_err("overlay changeset post-remove notify error %d\n",
                       ret_tmp);
                if (!ret)
                        ret = ret_tmp;
        }

        free_overlay_changeset(ovcs);

out_unlock:
        mutex_unlock(&of_mutex);

out:
        pr_debug("%s() err=%d\n", __func__, ret);

        return ret;
}
EXPORT_SYMBOL_GPL(of_overlay_remove);

/**
 * of_overlay_remove_all() - Reverts and frees all overlay changesets
 *
 * Removes all overlays from the system in the correct order.
 *
 * Returns 0 on success, or a negative error number
 */
int of_overlay_remove_all(void)
{
        struct overlay_changeset *ovcs, *ovcs_n;
        int ret;

        /* the tail of list is guaranteed to be safe to remove */
        list_for_each_entry_safe_reverse(ovcs, ovcs_n, &ovcs_list, ovcs_list) {
                ret = of_overlay_remove(&ovcs->id);
                if (ret)
                        return ret;
        }

        return 0;
}
EXPORT_SYMBOL_GPL(of_overlay_remove_all);