/*
 * ACPI device specific properties support.
 *
 * Copyright (C) 2014, Intel Corporation
 * All rights reserved.
 *
 * Authors: Mika Westerberg <mika.westerberg@linux.intel.com>
 *          Darren Hart <dvhart@linux.intel.com>
 *          Rafael J. Wysocki <rafael.j.wysocki@intel.com>
 *
 * 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.
 */

#include <linux/acpi.h>
#include <linux/device.h>
#include <linux/export.h>

#include "internal.h"

static int acpi_data_get_property_array(struct acpi_device_data *data,
                                        const char *name,
                                        acpi_object_type type,
                                        const union acpi_object **obj);

/* ACPI _DSD device properties UUID: daffd814-6eba-4d8c-8a91-bc9bbf4aa301 */
static const u8 prp_uuid[16] = {
        0x14, 0xd8, 0xff, 0xda, 0xba, 0x6e, 0x8c, 0x4d,
        0x8a, 0x91, 0xbc, 0x9b, 0xbf, 0x4a, 0xa3, 0x01
};
/* ACPI _DSD data subnodes UUID: dbb8e3e6-5886-4ba6-8795-1319f52a966b */
static const u8 ads_uuid[16] = {
        0xe6, 0xe3, 0xb8, 0xdb, 0x86, 0x58, 0xa6, 0x4b,
        0x87, 0x95, 0x13, 0x19, 0xf5, 0x2a, 0x96, 0x6b
};

static bool acpi_enumerate_nondev_subnodes(acpi_handle scope,
                                           const union acpi_object *desc,
                                           struct acpi_device_data *data);
static bool acpi_extract_properties(const union acpi_object *desc,
                                    struct acpi_device_data *data);

static bool acpi_nondev_subnode_ok(acpi_handle scope,
                                   const union acpi_object *link,
                                   struct list_head *list)
{
        struct acpi_buffer buf = { ACPI_ALLOCATE_BUFFER };
        struct acpi_data_node *dn;
        acpi_handle handle;
        acpi_status status;

        dn = kzalloc(sizeof(*dn), GFP_KERNEL);
        if (!dn)
                return false;

        dn->name = link->package.elements[0].string.pointer;
        dn->fwnode.type = FWNODE_ACPI_DATA;
        INIT_LIST_HEAD(&dn->data.subnodes);

        status = acpi_get_handle(scope, link->package.elements[1].string.pointer,
                                 &handle);
        if (ACPI_FAILURE(status))
                goto fail;

        status = acpi_evaluate_object_typed(handle, NULL, NULL, &buf,
                                            ACPI_TYPE_PACKAGE);
        if (ACPI_FAILURE(status))
                goto fail;

        if (acpi_extract_properties(buf.pointer, &dn->data))
                dn->handle = handle;

        /*
         * The scope for the subnode object lookup is the one of the namespace
         * node (device) containing the object that has returned the package.
         * That is, it's the scope of that object's parent.
         */
        status = acpi_get_parent(handle, &scope);
        if (ACPI_SUCCESS(status)
            && acpi_enumerate_nondev_subnodes(scope, buf.pointer, &dn->data))
                dn->handle = handle;

        if (dn->handle) {
                dn->data.pointer = buf.pointer;
                list_add_tail(&dn->sibling, list);
                return true;
        }

        acpi_handle_debug(handle, "Invalid properties/subnodes data, skipping\n");

 fail:
        ACPI_FREE(buf.pointer);
        kfree(dn);
        return false;
}

static int acpi_add_nondev_subnodes(acpi_handle scope,
                                    const union acpi_object *links,
                                    struct list_head *list)
{
        bool ret = false;
        int i;

        for (i = 0; i < links->package.count; i++) {
                const union acpi_object *link;

                link = &links->package.elements[i];
                /* Only two elements allowed, both must be strings. */
                if (link->package.count == 2
                    && link->package.elements[0].type == ACPI_TYPE_STRING
                    && link->package.elements[1].type == ACPI_TYPE_STRING
                    && acpi_nondev_subnode_ok(scope, link, list))
                        ret = true;
        }

        return ret;
}

static bool acpi_enumerate_nondev_subnodes(acpi_handle scope,
                                           const union acpi_object *desc,
                                           struct acpi_device_data *data)
{
        int i;

        /* Look for the ACPI data subnodes UUID. */
        for (i = 0; i < desc->package.count; i += 2) {
                const union acpi_object *uuid, *links;

                uuid = &desc->package.elements[i];
                links = &desc->package.elements[i + 1];

                /*
                 * The first element must be a UUID and the second one must be
                 * a package.
                 */
                if (uuid->type != ACPI_TYPE_BUFFER || uuid->buffer.length != 16
                    || links->type != ACPI_TYPE_PACKAGE)
                        break;

                if (memcmp(uuid->buffer.pointer, ads_uuid, sizeof(ads_uuid)))
                        continue;

                return acpi_add_nondev_subnodes(scope, links, &data->subnodes);
        }

        return false;
}

static bool acpi_property_value_ok(const union acpi_object *value)
{
        int j;

        /*
         * The value must be an integer, a string, a reference, or a package
         * whose every element must be an integer, a string, or a reference.
         */
        switch (value->type) {
        case ACPI_TYPE_INTEGER:
        case ACPI_TYPE_STRING:
        case ACPI_TYPE_LOCAL_REFERENCE:
                return true;

        case ACPI_TYPE_PACKAGE:
                for (j = 0; j < value->package.count; j++)
                        switch (value->package.elements[j].type) {
                        case ACPI_TYPE_INTEGER:
                        case ACPI_TYPE_STRING:
                        case ACPI_TYPE_LOCAL_REFERENCE:
                                continue;

                        default:
                                return false;
                        }

                return true;
        }
        return false;
}

static bool acpi_properties_format_valid(const union acpi_object *properties)
{
        int i;

        for (i = 0; i < properties->package.count; i++) {
                const union acpi_object *property;

                property = &properties->package.elements[i];
                /*
                 * Only two elements allowed, the first one must be a string and
                 * the second one has to satisfy certain conditions.
                 */
                if (property->package.count != 2
                    || property->package.elements[0].type != ACPI_TYPE_STRING
                    || !acpi_property_value_ok(&property->package.elements[1]))
                        return false;
        }
        return true;
}

static void acpi_init_of_compatible(struct acpi_device *adev)
{
        const union acpi_object *of_compatible;
        int ret;

        ret = acpi_data_get_property_array(&adev->data, "compatible",
                                           ACPI_TYPE_STRING, &of_compatible);
        if (ret) {
                ret = acpi_dev_get_property(adev, "compatible",
                                            ACPI_TYPE_STRING, &of_compatible);
                if (ret) {
                        if (adev->parent
                            && adev->parent->flags.of_compatible_ok)
                                goto out;

                        return;
                }
        }
        adev->data.of_compatible = of_compatible;

 out:
        adev->flags.of_compatible_ok = 1;
}

static bool acpi_extract_properties(const union acpi_object *desc,
                                    struct acpi_device_data *data)
{
        int i;

        if (desc->package.count % 2)
                return false;

        /* Look for the device properties UUID. */
        for (i = 0; i < desc->package.count; i += 2) {
                const union acpi_object *uuid, *properties;

                uuid = &desc->package.elements[i];
                properties = &desc->package.elements[i + 1];

                /*
                 * The first element must be a UUID and the second one must be
                 * a package.
                 */
                if (uuid->type != ACPI_TYPE_BUFFER || uuid->buffer.length != 16
                    || properties->type != ACPI_TYPE_PACKAGE)
                        break;

                if (memcmp(uuid->buffer.pointer, prp_uuid, sizeof(prp_uuid)))
                        continue;

                /*
                 * We found the matching UUID. Now validate the format of the
                 * package immediately following it.
                 */
                if (!acpi_properties_format_valid(properties))
                        break;

                data->properties = properties;
                return true;
        }

        return false;
}

void acpi_init_properties(struct acpi_device *adev)
{
        struct acpi_buffer buf = { ACPI_ALLOCATE_BUFFER };
        struct acpi_hardware_id *hwid;
        acpi_status status;
        bool acpi_of = false;

        INIT_LIST_HEAD(&adev->data.subnodes);

        /*
         * Check if ACPI_DT_NAMESPACE_HID is present and inthat case we fill in
         * Device Tree compatible properties for this device.
         */
        list_for_each_entry(hwid, &adev->pnp.ids, list) {
                if (!strcmp(hwid->id, ACPI_DT_NAMESPACE_HID)) {
                        acpi_of = true;
                        break;
                }
        }

        status = acpi_evaluate_object_typed(adev->handle, "_DSD", NULL, &buf,
                                            ACPI_TYPE_PACKAGE);
        if (ACPI_FAILURE(status))
                goto out;

        if (acpi_extract_properties(buf.pointer, &adev->data)) {
                adev->data.pointer = buf.pointer;
                if (acpi_of)
                        acpi_init_of_compatible(adev);
        }
        if (acpi_enumerate_nondev_subnodes(adev->handle, buf.pointer, &adev->data))
                adev->data.pointer = buf.pointer;

        if (!adev->data.pointer) {
                acpi_handle_debug(adev->handle, "Invalid _DSD data, skipping\n");
                ACPI_FREE(buf.pointer);
        }

 out:
        if (acpi_of && !adev->flags.of_compatible_ok)
                acpi_handle_info(adev->handle,
                         ACPI_DT_NAMESPACE_HID " requires 'compatible' property\n");
}

static void acpi_destroy_nondev_subnodes(struct list_head *list)
{
        struct acpi_data_node *dn, *next;

        if (list_empty(list))
                return;

        list_for_each_entry_safe_reverse(dn, next, list, sibling) {
                acpi_destroy_nondev_subnodes(&dn->data.subnodes);
                wait_for_completion(&dn->kobj_done);
                list_del(&dn->sibling);
                ACPI_FREE((void *)dn->data.pointer);
                kfree(dn);
        }
}

void acpi_free_properties(struct acpi_device *adev)
{
        acpi_destroy_nondev_subnodes(&adev->data.subnodes);
        ACPI_FREE((void *)adev->data.pointer);
        adev->data.of_compatible = NULL;
        adev->data.pointer = NULL;
        adev->data.properties = NULL;
}

/**
 * acpi_data_get_property - return an ACPI property with given name
 * @data: ACPI device deta object to get the property from
 * @name: Name of the property
 * @type: Expected property type
 * @obj: Location to store the property value (if not %NULL)
 *
 * Look up a property with @name and store a pointer to the resulting ACPI
 * object at the location pointed to by @obj if found.
 *
 * Callers must not attempt to free the returned objects.  These objects will be
 * freed by the ACPI core automatically during the removal of @data.
 *
 * Return: %0 if property with @name has been found (success),
 *         %-EINVAL if the arguments are invalid,
 *         %-EINVAL if the property doesn't exist,
 *         %-EPROTO if the property value type doesn't match @type.
 */
static int acpi_data_get_property(struct acpi_device_data *data,
                                  const char *name, acpi_object_type type,
                                  const union acpi_object **obj)
{
        const union acpi_object *properties;
        int i;

        if (!data || !name)
                return -EINVAL;

        if (!data->pointer || !data->properties)
                return -EINVAL;

        properties = data->properties;
        for (i = 0; i < properties->package.count; i++) {
                const union acpi_object *propname, *propvalue;
                const union acpi_object *property;

                property = &properties->package.elements[i];

                propname = &property->package.elements[0];
                propvalue = &property->package.elements[1];

                if (!strcmp(name, propname->string.pointer)) {
                        if (type != ACPI_TYPE_ANY && propvalue->type != type)
                                return -EPROTO;
                        if (obj)
                                *obj = propvalue;

                        return 0;
                }
        }
        return -EINVAL;
}

/**
 * acpi_dev_get_property - return an ACPI property with given name.
 * @adev: ACPI device to get the property from.
 * @name: Name of the property.
 * @type: Expected property type.
 * @obj: Location to store the property value (if not %NULL).
 */
int acpi_dev_get_property(struct acpi_device *adev, const char *name,
                          acpi_object_type type, const union acpi_object **obj)
{
        return adev ? acpi_data_get_property(&adev->data, name, type, obj) : -EINVAL;
}
EXPORT_SYMBOL_GPL(acpi_dev_get_property);

static struct acpi_device_data *acpi_device_data_of_node(struct fwnode_handle *fwnode)
{
        if (fwnode->type == FWNODE_ACPI) {
                struct acpi_device *adev = to_acpi_device_node(fwnode);
                return &adev->data;
        } else if (fwnode->type == FWNODE_ACPI_DATA) {
                struct acpi_data_node *dn = to_acpi_data_node(fwnode);
                return &dn->data;
        }
        return NULL;
}

/**
 * acpi_node_prop_get - return an ACPI property with given name.
 * @fwnode: Firmware node to get the property from.
 * @propname: Name of the property.
 * @valptr: Location to store a pointer to the property value (if not %NULL).
 */
int acpi_node_prop_get(struct fwnode_handle *fwnode, const char *propname,
                       void **valptr)
{
        return acpi_data_get_property(acpi_device_data_of_node(fwnode),
                                      propname, ACPI_TYPE_ANY,
                                      (const union acpi_object **)valptr);
}

/**
 * acpi_data_get_property_array - return an ACPI array property with given name
 * @adev: ACPI data object to get the property from
 * @name: Name of the property
 * @type: Expected type of array elements
 * @obj: Location to store a pointer to the property value (if not NULL)
 *
 * Look up an array property with @name and store a pointer to the resulting
 * ACPI object at the location pointed to by @obj if found.
 *
 * Callers must not attempt to free the returned objects.  Those objects will be
 * freed by the ACPI core automatically during the removal of @data.
 *
 * Return: %0 if array property (package) with @name has been found (success),
 *         %-EINVAL if the arguments are invalid,
 *         %-EINVAL if the property doesn't exist,
 *         %-EPROTO if the property is not a package or the type of its elements
 *           doesn't match @type.
 */
static int acpi_data_get_property_array(struct acpi_device_data *data,
                                        const char *name,
                                        acpi_object_type type,
                                        const union acpi_object **obj)
{
        const union acpi_object *prop;
        int ret, i;

        ret = acpi_data_get_property(data, name, ACPI_TYPE_PACKAGE, &prop);
        if (ret)
                return ret;

        if (type != ACPI_TYPE_ANY) {
                /* Check that all elements are of correct type. */
                for (i = 0; i < prop->package.count; i++)
                        if (prop->package.elements[i].type != type)
                                return -EPROTO;
        }
        if (obj)
                *obj = prop;

        return 0;
}

/**
 * acpi_data_get_property_reference - returns handle to the referenced object
 * @data: ACPI device data object containing the property
 * @propname: Name of the property
 * @index: Index of the reference to return
 * @args: Location to store the returned reference with optional arguments
 *
 * Find property with @name, verifify that it is a package containing at least
 * one object reference and if so, store the ACPI device object pointer to the
 * target object in @args->adev.  If the reference includes arguments, store
 * them in the @args->args[] array.
 *
 * If there's more than one reference in the property value package, @index is
 * used to select the one to return.
 *
 * Return: %0 on success, negative error code on failure.
 */
static int acpi_data_get_property_reference(struct acpi_device_data *data,
                                            const char *propname, size_t index,
                                            struct acpi_reference_args *args)
{
        const union acpi_object *element, *end;
        const union acpi_object *obj;
        struct acpi_device *device;
        int ret, idx = 0;

        ret = acpi_data_get_property(data, propname, ACPI_TYPE_ANY, &obj);
        if (ret)
                return ret;

        /*
         * The simplest case is when the value is a single reference.  Just
         * return that reference then.
         */
        if (obj->type == ACPI_TYPE_LOCAL_REFERENCE) {
                if (index)
                        return -EINVAL;

                ret = acpi_bus_get_device(obj->reference.handle, &device);
                if (ret)
                        return ret;

                args->adev = device;
                args->nargs = 0;
                return 0;
        }

        /*
         * If it is not a single reference, then it is a package of
         * references followed by number of ints as follows:
         *
         *  Package () { REF, INT, REF, INT, INT }
         *
         * The index argument is then used to determine which reference
         * the caller wants (along with the arguments).
         */
        if (obj->type != ACPI_TYPE_PACKAGE || index >= obj->package.count)
                return -EPROTO;

        element = obj->package.elements;
        end = element + obj->package.count;

        while (element < end) {
                u32 nargs, i;

                if (element->type != ACPI_TYPE_LOCAL_REFERENCE)
                        return -EPROTO;

                ret = acpi_bus_get_device(element->reference.handle, &device);
                if (ret)
                        return -ENODEV;

                element++;
                nargs = 0;

                /* assume following integer elements are all args */
                for (i = 0; element + i < end; i++) {
                        int type = element[i].type;

                        if (type == ACPI_TYPE_INTEGER)
                                nargs++;
                        else if (type == ACPI_TYPE_LOCAL_REFERENCE)
                                break;
                        else
                                return -EPROTO;
                }

                if (idx++ == index) {
                        args->adev = device;
                        args->nargs = nargs;
                        for (i = 0; i < nargs; i++)
                                args->args[i] = element[i].integer.value;

                        return 0;
                }

                element += nargs;
        }

        return -EPROTO;
}

/**
 * acpi_node_get_property_reference - get a handle to the referenced object.
 * @fwnode: Firmware node to get the property from.
 * @propname: Name of the property.
 * @index: Index of the reference to return.
 * @args: Location to store the returned reference with optional arguments.
 */
int acpi_node_get_property_reference(struct fwnode_handle *fwnode,
                                     const char *name, size_t index,
                                     struct acpi_reference_args *args)
{
        struct acpi_device_data *data = acpi_device_data_of_node(fwnode);

        return data ? acpi_data_get_property_reference(data, name, index, args) : -EINVAL;
}
EXPORT_SYMBOL_GPL(acpi_node_get_property_reference);

static int acpi_data_prop_read_single(struct acpi_device_data *data,
                                      const char *propname,
                                      enum dev_prop_type proptype, void *val)
{
        const union acpi_object *obj;
        int ret;

        if (!val)
                return -EINVAL;

        if (proptype >= DEV_PROP_U8 && proptype <= DEV_PROP_U64) {
                ret = acpi_data_get_property(data, propname, ACPI_TYPE_INTEGER, &obj);
                if (ret)
                        return ret;

                switch (proptype) {
                case DEV_PROP_U8:
                        if (obj->integer.value > U8_MAX)
                                return -EOVERFLOW;
                        *(u8 *)val = obj->integer.value;
                        break;
                case DEV_PROP_U16:
                        if (obj->integer.value > U16_MAX)
                                return -EOVERFLOW;
                        *(u16 *)val = obj->integer.value;
                        break;
                case DEV_PROP_U32:
                        if (obj->integer.value > U32_MAX)
                                return -EOVERFLOW;
                        *(u32 *)val = obj->integer.value;
                        break;
                default:
                        *(u64 *)val = obj->integer.value;
                        break;
                }
        } else if (proptype == DEV_PROP_STRING) {
                ret = acpi_data_get_property(data, propname, ACPI_TYPE_STRING, &obj);
                if (ret)
                        return ret;

                *(char **)val = obj->string.pointer;
        } else {
                ret = -EINVAL;
        }
        return ret;
}

int acpi_dev_prop_read_single(struct acpi_device *adev, const char *propname,
                              enum dev_prop_type proptype, void *val)
{
        return adev ? acpi_data_prop_read_single(&adev->data, propname, proptype, val) : -EINVAL;
}

static int acpi_copy_property_array_u8(const union acpi_object *items, u8 *val,
                                       size_t nval)
{
        int i;

        for (i = 0; i < nval; i++) {
                if (items[i].type != ACPI_TYPE_INTEGER)
                        return -EPROTO;
                if (items[i].integer.value > U8_MAX)
                        return -EOVERFLOW;

                val[i] = items[i].integer.value;
        }
        return 0;
}

static int acpi_copy_property_array_u16(const union acpi_object *items,
                                        u16 *val, size_t nval)
{
        int i;

        for (i = 0; i < nval; i++) {
                if (items[i].type != ACPI_TYPE_INTEGER)
                        return -EPROTO;
                if (items[i].integer.value > U16_MAX)
                        return -EOVERFLOW;

                val[i] = items[i].integer.value;
        }
        return 0;
}

static int acpi_copy_property_array_u32(const union acpi_object *items,
                                        u32 *val, size_t nval)
{
        int i;

        for (i = 0; i < nval; i++) {
                if (items[i].type != ACPI_TYPE_INTEGER)
                        return -EPROTO;
                if (items[i].integer.value > U32_MAX)
                        return -EOVERFLOW;

                val[i] = items[i].integer.value;
        }
        return 0;
}

static int acpi_copy_property_array_u64(const union acpi_object *items,
                                        u64 *val, size_t nval)
{
        int i;

        for (i = 0; i < nval; i++) {
                if (items[i].type != ACPI_TYPE_INTEGER)
                        return -EPROTO;

                val[i] = items[i].integer.value;
        }
        return 0;
}

static int acpi_copy_property_array_string(const union acpi_object *items,
                                           char **val, size_t nval)
{
        int i;

        for (i = 0; i < nval; i++) {
                if (items[i].type != ACPI_TYPE_STRING)
                        return -EPROTO;

                val[i] = items[i].string.pointer;
        }
        return 0;
}

static int acpi_data_prop_read(struct acpi_device_data *data,
                               const char *propname,
                               enum dev_prop_type proptype,
                               void *val, size_t nval)
{
        const union acpi_object *obj;
        const union acpi_object *items;
        int ret;

        if (val && nval == 1) {
                ret = acpi_data_prop_read_single(data, propname, proptype, val);
                if (!ret)
                        return ret;
        }

        ret = acpi_data_get_property_array(data, propname, ACPI_TYPE_ANY, &obj);
        if (ret)
                return ret;

        if (!val)
                return obj->package.count;

        if (nval > obj->package.count)
                return -EOVERFLOW;
        else if (nval <= 0)
                return -EINVAL;

        items = obj->package.elements;

        switch (proptype) {
        case DEV_PROP_U8:
                ret = acpi_copy_property_array_u8(items, (u8 *)val, nval);
                break;
        case DEV_PROP_U16:
                ret = acpi_copy_property_array_u16(items, (u16 *)val, nval);
                break;
        case DEV_PROP_U32:
                ret = acpi_copy_property_array_u32(items, (u32 *)val, nval);
                break;
        case DEV_PROP_U64:
                ret = acpi_copy_property_array_u64(items, (u64 *)val, nval);
                break;
        case DEV_PROP_STRING:
                ret = acpi_copy_property_array_string(items, (char **)val, nval);
                break;
        default:
                ret = -EINVAL;
                break;
        }
        return ret;
}

int acpi_dev_prop_read(struct acpi_device *adev, const char *propname,
                       enum dev_prop_type proptype, void *val, size_t nval)
{
        return adev ? acpi_data_prop_read(&adev->data, propname, proptype, val, nval) : -EINVAL;
}

/**
 * acpi_node_prop_read - retrieve the value of an ACPI property with given name.
 * @fwnode: Firmware node to get the property from.
 * @propname: Name of the property.
 * @proptype: Expected property type.
 * @val: Location to store the property value (if not %NULL).
 * @nval: Size of the array pointed to by @val.
 *
 * If @val is %NULL, return the number of array elements comprising the value
 * of the property.  Otherwise, read at most @nval values to the array at the
 * location pointed to by @val.
 */
int acpi_node_prop_read(struct fwnode_handle *fwnode,  const char *propname,
                        enum dev_prop_type proptype, void *val, size_t nval)
{
        return acpi_data_prop_read(acpi_device_data_of_node(fwnode),
                                   propname, proptype, val, nval);
}

/**
 * acpi_get_next_subnode - Return the next child node handle for a device.
 * @dev: Device to find the next child node for.
 * @child: Handle to one of the device's child nodes or a null handle.
 */
struct fwnode_handle *acpi_get_next_subnode(struct device *dev,
                                            struct fwnode_handle *child)
{
        struct acpi_device *adev = ACPI_COMPANION(dev);
        struct list_head *head, *next;

        if (!adev)
                return NULL;

        if (!child || child->type == FWNODE_ACPI) {
                head = &adev->children;
                if (list_empty(head))
                        goto nondev;

                if (child) {
                        adev = to_acpi_device_node(child);
                        next = adev->node.next;
                        if (next == head) {
                                child = NULL;
                                adev = ACPI_COMPANION(dev);
                                goto nondev;
                        }
                        adev = list_entry(next, struct acpi_device, node);
                } else {
                        adev = list_first_entry(head, struct acpi_device, node);
                }
                return acpi_fwnode_handle(adev);
        }

 nondev:
        if (!child || child->type == FWNODE_ACPI_DATA) {
                struct acpi_data_node *dn;

                head = &adev->data.subnodes;
                if (list_empty(head))
                        return NULL;

                if (child) {
                        dn = to_acpi_data_node(child);
                        next = dn->sibling.next;
                        if (next == head)
                                return NULL;

                        dn = list_entry(next, struct acpi_data_node, sibling);
                } else {
                        dn = list_first_entry(head, struct acpi_data_node, sibling);
                }
                return &dn->fwnode;
        }
        return NULL;
}