// SPDX-License-Identifier: GPL-2.0
/*
 * pptt.c - parsing of Processor Properties Topology Table (PPTT)
 *
 * Copyright (C) 2018, ARM
 *
 * This file implements parsing of the Processor Properties Topology Table
 * which is optionally used to describe the processor and cache topology.
 * Due to the relative pointers used throughout the table, this doesn't
 * leverage the existing subtable parsing in the kernel.
 *
 * The PPTT structure is an inverted tree, with each node potentially
 * holding one or two inverted tree data structures describing
 * the caches available at that level. Each cache structure optionally
 * contains properties describing the cache at a given level which can be
 * used to override hardware probed values.
 */
#define pr_fmt(fmt) "ACPI PPTT: " fmt

#include <linux/acpi.h>
#include <linux/cacheinfo.h>
#include <acpi/processor.h>

static struct acpi_subtable_header *fetch_pptt_subtable(struct acpi_table_header *table_hdr,
                                                        u32 pptt_ref)
{
        struct acpi_subtable_header *entry;

        /* there isn't a subtable at reference 0 */
        if (pptt_ref < sizeof(struct acpi_subtable_header))
                return NULL;

        if (pptt_ref + sizeof(struct acpi_subtable_header) > table_hdr->length)
                return NULL;

        entry = ACPI_ADD_PTR(struct acpi_subtable_header, table_hdr, pptt_ref);

        if (entry->length == 0)
                return NULL;

        if (pptt_ref + entry->length > table_hdr->length)
                return NULL;

        return entry;
}

static struct acpi_pptt_processor *fetch_pptt_node(struct acpi_table_header *table_hdr,
                                                   u32 pptt_ref)
{
        return (struct acpi_pptt_processor *)fetch_pptt_subtable(table_hdr, pptt_ref);
}

static struct acpi_pptt_cache *fetch_pptt_cache(struct acpi_table_header *table_hdr,
                                                u32 pptt_ref)
{
        return (struct acpi_pptt_cache *)fetch_pptt_subtable(table_hdr, pptt_ref);
}

static struct acpi_subtable_header *acpi_get_pptt_resource(struct acpi_table_header *table_hdr,
                                                           struct acpi_pptt_processor *node,
                                                           int resource)
{
        u32 *ref;

        if (resource >= node->number_of_priv_resources)
                return NULL;

        ref = ACPI_ADD_PTR(u32, node, sizeof(struct acpi_pptt_processor));
        ref += resource;

        return fetch_pptt_subtable(table_hdr, *ref);
}

static inline bool acpi_pptt_match_type(int table_type, int type)
{
        return ((table_type & ACPI_PPTT_MASK_CACHE_TYPE) == type ||
                table_type & ACPI_PPTT_CACHE_TYPE_UNIFIED & type);
}

/**
 * acpi_pptt_walk_cache() - Attempt to find the requested acpi_pptt_cache
 * @table_hdr: Pointer to the head of the PPTT table
 * @local_level: passed res reflects this cache level
 * @res: cache resource in the PPTT we want to walk
 * @found: returns a pointer to the requested level if found
 * @level: the requested cache level
 * @type: the requested cache type
 *
 * Attempt to find a given cache level, while counting the max number
 * of cache levels for the cache node.
 *
 * Given a pptt resource, verify that it is a cache node, then walk
 * down each level of caches, counting how many levels are found
 * as well as checking the cache type (icache, dcache, unified). If a
 * level & type match, then we set found, and continue the search.
 * Once the entire cache branch has been walked return its max
 * depth.
 *
 * Return: The cache structure and the level we terminated with.
 */
static int acpi_pptt_walk_cache(struct acpi_table_header *table_hdr,
                                int local_level,
                                struct acpi_subtable_header *res,
                                struct acpi_pptt_cache **found,
                                int level, int type)
{
        struct acpi_pptt_cache *cache;

        if (res->type != ACPI_PPTT_TYPE_CACHE)
                return 0;

        cache = (struct acpi_pptt_cache *) res;
        while (cache) {
                local_level++;

                if (local_level == level &&
                    cache->flags & ACPI_PPTT_CACHE_TYPE_VALID &&
                    acpi_pptt_match_type(cache->attributes, type)) {
                        if (*found != NULL && cache != *found)
                                pr_warn("Found duplicate cache level/type unable to determine uniqueness\n");

                        pr_debug("Found cache @ level %d\n", level);
                        *found = cache;
                        /*
                         * continue looking at this node's resource list
                         * to verify that we don't find a duplicate
                         * cache node.
                         */
                }
                cache = fetch_pptt_cache(table_hdr, cache->next_level_of_cache);
        }
        return local_level;
}

static struct acpi_pptt_cache *acpi_find_cache_level(struct acpi_table_header *table_hdr,
                                                     struct acpi_pptt_processor *cpu_node,
                                                     int *starting_level, int level,
                                                     int type)
{
        struct acpi_subtable_header *res;
        int number_of_levels = *starting_level;
        int resource = 0;
        struct acpi_pptt_cache *ret = NULL;
        int local_level;

        /* walk down from processor node */
        while ((res = acpi_get_pptt_resource(table_hdr, cpu_node, resource))) {
                resource++;

                local_level = acpi_pptt_walk_cache(table_hdr, *starting_level,
                                                   res, &ret, level, type);
                /*
                 * we are looking for the max depth. Since its potentially
                 * possible for a given node to have resources with differing
                 * depths verify that the depth we have found is the largest.
                 */
                if (number_of_levels < local_level)
                        number_of_levels = local_level;
        }
        if (number_of_levels > *starting_level)
                *starting_level = number_of_levels;

        return ret;
}

/**
 * acpi_count_levels() - Given a PPTT table, and a CPU node, count the caches
 * @table_hdr: Pointer to the head of the PPTT table
 * @cpu_node: processor node we wish to count caches for
 *
 * Given a processor node containing a processing unit, walk into it and count
 * how many levels exist solely for it, and then walk up each level until we hit
 * the root node (ignore the package level because it may be possible to have
 * caches that exist across packages). Count the number of cache levels that
 * exist at each level on the way up.
 *
 * Return: Total number of levels found.
 */
static int acpi_count_levels(struct acpi_table_header *table_hdr,
                             struct acpi_pptt_processor *cpu_node)
{
        int total_levels = 0;

        do {
                acpi_find_cache_level(table_hdr, cpu_node, &total_levels, 0, 0);
                cpu_node = fetch_pptt_node(table_hdr, cpu_node->parent);
        } while (cpu_node);

        return total_levels;
}

/**
 * acpi_pptt_leaf_node() - Given a processor node, determine if its a leaf
 * @table_hdr: Pointer to the head of the PPTT table
 * @node: passed node is checked to see if its a leaf
 *
 * Determine if the *node parameter is a leaf node by iterating the
 * PPTT table, looking for nodes which reference it.
 *
 * Return: 0 if we find a node referencing the passed node (or table error),
 * or 1 if we don't.
 */
static int acpi_pptt_leaf_node(struct acpi_table_header *table_hdr,
                               struct acpi_pptt_processor *node)
{
        struct acpi_subtable_header *entry;
        unsigned long table_end;
        u32 node_entry;
        struct acpi_pptt_processor *cpu_node;
        u32 proc_sz;

        if (table_hdr->revision > 1)
                return (node->flags & ACPI_PPTT_ACPI_LEAF_NODE);

        table_end = (unsigned long)table_hdr + table_hdr->length;
        node_entry = ACPI_PTR_DIFF(node, table_hdr);
        entry = ACPI_ADD_PTR(struct acpi_subtable_header, table_hdr,
                             sizeof(struct acpi_table_pptt));
        proc_sz = sizeof(struct acpi_pptt_processor *);

        while ((unsigned long)entry + proc_sz < table_end) {
                cpu_node = (struct acpi_pptt_processor *)entry;
                if (entry->type == ACPI_PPTT_TYPE_PROCESSOR &&
                    cpu_node->parent == node_entry)
                        return 0;
                if (entry->length == 0)
                        return 0;
                entry = ACPI_ADD_PTR(struct acpi_subtable_header, entry,
                                     entry->length);

        }
        return 1;
}

/**
 * acpi_find_processor_node() - Given a PPTT table find the requested processor
 * @table_hdr:  Pointer to the head of the PPTT table
 * @acpi_cpu_id: CPU we are searching for
 *
 * Find the subtable entry describing the provided processor.
 * This is done by iterating the PPTT table looking for processor nodes
 * which have an acpi_processor_id that matches the acpi_cpu_id parameter
 * passed into the function. If we find a node that matches this criteria
 * we verify that its a leaf node in the topology rather than depending
 * on the valid flag, which doesn't need to be set for leaf nodes.
 *
 * Return: NULL, or the processors acpi_pptt_processor*
 */
static struct acpi_pptt_processor *acpi_find_processor_node(struct acpi_table_header *table_hdr,
                                                            u32 acpi_cpu_id)
{
        struct acpi_subtable_header *entry;
        unsigned long table_end;
        struct acpi_pptt_processor *cpu_node;
        u32 proc_sz;

        table_end = (unsigned long)table_hdr + table_hdr->length;
        entry = ACPI_ADD_PTR(struct acpi_subtable_header, table_hdr,
                             sizeof(struct acpi_table_pptt));
        proc_sz = sizeof(struct acpi_pptt_processor *);

        /* find the processor structure associated with this cpuid */
        while ((unsigned long)entry + proc_sz < table_end) {
                cpu_node = (struct acpi_pptt_processor *)entry;

                if (entry->length == 0) {
                        pr_warn("Invalid zero length subtable\n");
                        break;
                }
                if (entry->type == ACPI_PPTT_TYPE_PROCESSOR &&
                    acpi_cpu_id == cpu_node->acpi_processor_id &&
                     acpi_pptt_leaf_node(table_hdr, cpu_node)) {
                        return (struct acpi_pptt_processor *)entry;
                }

                entry = ACPI_ADD_PTR(struct acpi_subtable_header, entry,
                                     entry->length);
        }

        return NULL;
}

static int acpi_find_cache_levels(struct acpi_table_header *table_hdr,
                                  u32 acpi_cpu_id)
{
        int number_of_levels = 0;
        struct acpi_pptt_processor *cpu;

        cpu = acpi_find_processor_node(table_hdr, acpi_cpu_id);
        if (cpu)
                number_of_levels = acpi_count_levels(table_hdr, cpu);

        return number_of_levels;
}

static u8 acpi_cache_type(enum cache_type type)
{
        switch (type) {
        case CACHE_TYPE_DATA:
                pr_debug("Looking for data cache\n");
                return ACPI_PPTT_CACHE_TYPE_DATA;
        case CACHE_TYPE_INST:
                pr_debug("Looking for instruction cache\n");
                return ACPI_PPTT_CACHE_TYPE_INSTR;
        default:
        case CACHE_TYPE_UNIFIED:
                pr_debug("Looking for unified cache\n");
                /*
                 * It is important that ACPI_PPTT_CACHE_TYPE_UNIFIED
                 * contains the bit pattern that will match both
                 * ACPI unified bit patterns because we use it later
                 * to match both cases.
                 */
                return ACPI_PPTT_CACHE_TYPE_UNIFIED;
        }
}

static struct acpi_pptt_cache *acpi_find_cache_node(struct acpi_table_header *table_hdr,
                                                    u32 acpi_cpu_id,
                                                    enum cache_type type,
                                                    unsigned int level,
                                                    struct acpi_pptt_processor **node)
{
        int total_levels = 0;
        struct acpi_pptt_cache *found = NULL;
        struct acpi_pptt_processor *cpu_node;
        u8 acpi_type = acpi_cache_type(type);

        pr_debug("Looking for CPU %d's level %d cache type %d\n",
                 acpi_cpu_id, level, acpi_type);

        cpu_node = acpi_find_processor_node(table_hdr, acpi_cpu_id);

        while (cpu_node && !found) {
                found = acpi_find_cache_level(table_hdr, cpu_node,
                                              &total_levels, level, acpi_type);
                *node = cpu_node;
                cpu_node = fetch_pptt_node(table_hdr, cpu_node->parent);
        }

        return found;
}

/**
 * update_cache_properties() - Update cacheinfo for the given processor
 * @this_leaf: Kernel cache info structure being updated
 * @found_cache: The PPTT node describing this cache instance
 * @cpu_node: A unique reference to describe this cache instance
 *
 * The ACPI spec implies that the fields in the cache structures are used to
 * extend and correct the information probed from the hardware. Lets only
 * set fields that we determine are VALID.
 *
 * Return: nothing. Side effect of updating the global cacheinfo
 */
static void update_cache_properties(struct cacheinfo *this_leaf,
                                    struct acpi_pptt_cache *found_cache,
                                    struct acpi_pptt_processor *cpu_node)
{
        this_leaf->fw_token = cpu_node;
        if (found_cache->flags & ACPI_PPTT_SIZE_PROPERTY_VALID)
                this_leaf->size = found_cache->size;
        if (found_cache->flags & ACPI_PPTT_LINE_SIZE_VALID)
                this_leaf->coherency_line_size = found_cache->line_size;
        if (found_cache->flags & ACPI_PPTT_NUMBER_OF_SETS_VALID)
                this_leaf->number_of_sets = found_cache->number_of_sets;
        if (found_cache->flags & ACPI_PPTT_ASSOCIATIVITY_VALID)
                this_leaf->ways_of_associativity = found_cache->associativity;
        if (found_cache->flags & ACPI_PPTT_WRITE_POLICY_VALID) {
                switch (found_cache->attributes & ACPI_PPTT_MASK_WRITE_POLICY) {
                case ACPI_PPTT_CACHE_POLICY_WT:
                        this_leaf->attributes = CACHE_WRITE_THROUGH;
                        break;
                case ACPI_PPTT_CACHE_POLICY_WB:
                        this_leaf->attributes = CACHE_WRITE_BACK;
                        break;
                }
        }
        if (found_cache->flags & ACPI_PPTT_ALLOCATION_TYPE_VALID) {
                switch (found_cache->attributes & ACPI_PPTT_MASK_ALLOCATION_TYPE) {
                case ACPI_PPTT_CACHE_READ_ALLOCATE:
                        this_leaf->attributes |= CACHE_READ_ALLOCATE;
                        break;
                case ACPI_PPTT_CACHE_WRITE_ALLOCATE:
                        this_leaf->attributes |= CACHE_WRITE_ALLOCATE;
                        break;
                case ACPI_PPTT_CACHE_RW_ALLOCATE:
                case ACPI_PPTT_CACHE_RW_ALLOCATE_ALT:
                        this_leaf->attributes |=
                                CACHE_READ_ALLOCATE | CACHE_WRITE_ALLOCATE;
                        break;
                }
        }
        /*
         * If cache type is NOCACHE, then the cache hasn't been specified
         * via other mechanisms.  Update the type if a cache type has been
         * provided.
         *
         * Note, we assume such caches are unified based on conventional system
         * design and known examples.  Significant work is required elsewhere to
         * fully support data/instruction only type caches which are only
         * specified in PPTT.
         */
        if (this_leaf->type == CACHE_TYPE_NOCACHE &&
            found_cache->flags & ACPI_PPTT_CACHE_TYPE_VALID)
                this_leaf->type = CACHE_TYPE_UNIFIED;
}

static void cache_setup_acpi_cpu(struct acpi_table_header *table,
                                 unsigned int cpu)
{
        struct acpi_pptt_cache *found_cache;
        struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
        u32 acpi_cpu_id = get_acpi_id_for_cpu(cpu);
        struct cacheinfo *this_leaf;
        unsigned int index = 0;
        struct acpi_pptt_processor *cpu_node = NULL;

        while (index < get_cpu_cacheinfo(cpu)->num_leaves) {
                this_leaf = this_cpu_ci->info_list + index;
                found_cache = acpi_find_cache_node(table, acpi_cpu_id,
                                                   this_leaf->type,
                                                   this_leaf->level,
                                                   &cpu_node);
                pr_debug("found = %p %p\n", found_cache, cpu_node);
                if (found_cache)
                        update_cache_properties(this_leaf,
                                                found_cache,
                                                cpu_node);

                index++;
        }
}

static bool flag_identical(struct acpi_table_header *table_hdr,
                           struct acpi_pptt_processor *cpu)
{
        struct acpi_pptt_processor *next;

        /* heterogeneous machines must use PPTT revision > 1 */
        if (table_hdr->revision < 2)
                return false;

        /* Locate the last node in the tree with IDENTICAL set */
        if (cpu->flags & ACPI_PPTT_ACPI_IDENTICAL) {
                next = fetch_pptt_node(table_hdr, cpu->parent);
                if (!(next && next->flags & ACPI_PPTT_ACPI_IDENTICAL))
                        return true;
        }

        return false;
}

/* Passing level values greater than this will result in search termination */
#define PPTT_ABORT_PACKAGE 0xFF

static struct acpi_pptt_processor *acpi_find_processor_tag(struct acpi_table_header *table_hdr,
                                                           struct acpi_pptt_processor *cpu,
                                                           int level, int flag)
{
        struct acpi_pptt_processor *prev_node;

        while (cpu && level) {
                /* special case the identical flag to find last identical */
                if (flag == ACPI_PPTT_ACPI_IDENTICAL) {
                        if (flag_identical(table_hdr, cpu))
                                break;
                } else if (cpu->flags & flag)
                        break;
                pr_debug("level %d\n", level);
                prev_node = fetch_pptt_node(table_hdr, cpu->parent);
                if (prev_node == NULL)
                        break;
                cpu = prev_node;
                level--;
        }
        return cpu;
}

static void acpi_pptt_warn_missing(void)
{
        pr_warn_once("No PPTT table found, CPU and cache topology may be inaccurate\n");
}

/**
 * topology_get_acpi_cpu_tag() - Find a unique topology value for a feature
 * @table: Pointer to the head of the PPTT table
 * @cpu: Kernel logical CPU number
 * @level: A level that terminates the search
 * @flag: A flag which terminates the search
 *
 * Get a unique value given a CPU, and a topology level, that can be
 * matched to determine which cpus share common topological features
 * at that level.
 *
 * Return: Unique value, or -ENOENT if unable to locate CPU
 */
static int topology_get_acpi_cpu_tag(struct acpi_table_header *table,
                                     unsigned int cpu, int level, int flag)
{
        struct acpi_pptt_processor *cpu_node;
        u32 acpi_cpu_id = get_acpi_id_for_cpu(cpu);

        cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
        if (cpu_node) {
                cpu_node = acpi_find_processor_tag(table, cpu_node,
                                                   level, flag);
                /*
                 * As per specification if the processor structure represents
                 * an actual processor, then ACPI processor ID must be valid.
                 * For processor containers ACPI_PPTT_ACPI_PROCESSOR_ID_VALID
                 * should be set if the UID is valid
                 */
                if (level == 0 ||
                    cpu_node->flags & ACPI_PPTT_ACPI_PROCESSOR_ID_VALID)
                        return cpu_node->acpi_processor_id;
                return ACPI_PTR_DIFF(cpu_node, table);
        }
        pr_warn_once("PPTT table found, but unable to locate core %d (%d)\n",
                    cpu, acpi_cpu_id);
        return -ENOENT;
}

static int find_acpi_cpu_topology_tag(unsigned int cpu, int level, int flag)
{
        struct acpi_table_header *table;
        acpi_status status;
        int retval;

        status = acpi_get_table(ACPI_SIG_PPTT, 0, &table);
        if (ACPI_FAILURE(status)) {
                acpi_pptt_warn_missing();
                return -ENOENT;
        }
        retval = topology_get_acpi_cpu_tag(table, cpu, level, flag);
        pr_debug("Topology Setup ACPI CPU %d, level %d ret = %d\n",
                 cpu, level, retval);
        acpi_put_table(table);

        return retval;
}

/**
 * acpi_find_last_cache_level() - Determines the number of cache levels for a PE
 * @cpu: Kernel logical CPU number
 *
 * Given a logical CPU number, returns the number of levels of cache represented
 * in the PPTT. Errors caused by lack of a PPTT table, or otherwise, return 0
 * indicating we didn't find any cache levels.
 *
 * Return: Cache levels visible to this core.
 */
int acpi_find_last_cache_level(unsigned int cpu)
{
        u32 acpi_cpu_id;
        struct acpi_table_header *table;
        int number_of_levels = 0;
        acpi_status status;

        pr_debug("Cache Setup find last level CPU=%d\n", cpu);

        acpi_cpu_id = get_acpi_id_for_cpu(cpu);
        status = acpi_get_table(ACPI_SIG_PPTT, 0, &table);
        if (ACPI_FAILURE(status)) {
                acpi_pptt_warn_missing();
        } else {
                number_of_levels = acpi_find_cache_levels(table, acpi_cpu_id);
                acpi_put_table(table);
        }
        pr_debug("Cache Setup find last level level=%d\n", number_of_levels);

        return number_of_levels;
}

/**
 * cache_setup_acpi() - Override CPU cache topology with data from the PPTT
 * @cpu: Kernel logical CPU number
 *
 * Updates the global cache info provided by cpu_get_cacheinfo()
 * when there are valid properties in the acpi_pptt_cache nodes. A
 * successful parse may not result in any updates if none of the
 * cache levels have any valid flags set.  Further, a unique value is
 * associated with each known CPU cache entry. This unique value
 * can be used to determine whether caches are shared between CPUs.
 *
 * Return: -ENOENT on failure to find table, or 0 on success
 */
int cache_setup_acpi(unsigned int cpu)
{
        struct acpi_table_header *table;
        acpi_status status;

        pr_debug("Cache Setup ACPI CPU %d\n", cpu);

        status = acpi_get_table(ACPI_SIG_PPTT, 0, &table);
        if (ACPI_FAILURE(status)) {
                acpi_pptt_warn_missing();
                return -ENOENT;
        }

        cache_setup_acpi_cpu(table, cpu);
        acpi_put_table(table);

        return status;
}

/**
 * find_acpi_cpu_topology() - Determine a unique topology value for a given CPU
 * @cpu: Kernel logical CPU number
 * @level: The topological level for which we would like a unique ID
 *
 * Determine a topology unique ID for each thread/core/cluster/mc_grouping
 * /socket/etc. This ID can then be used to group peers, which will have
 * matching ids.
 *
 * The search terminates when either the requested level is found or
 * we reach a root node. Levels beyond the termination point will return the
 * same unique ID. The unique id for level 0 is the acpi processor id. All
 * other levels beyond this use a generated value to uniquely identify
 * a topological feature.
 *
 * Return: -ENOENT if the PPTT doesn't exist, or the CPU cannot be found.
 * Otherwise returns a value which represents a unique topological feature.
 */
int find_acpi_cpu_topology(unsigned int cpu, int level)
{
        return find_acpi_cpu_topology_tag(cpu, level, 0);
}

/**
 * find_acpi_cpu_cache_topology() - Determine a unique cache topology value
 * @cpu: Kernel logical CPU number
 * @level: The cache level for which we would like a unique ID
 *
 * Determine a unique ID for each unified cache in the system
 *
 * Return: -ENOENT if the PPTT doesn't exist, or the CPU cannot be found.
 * Otherwise returns a value which represents a unique topological feature.
 */
int find_acpi_cpu_cache_topology(unsigned int cpu, int level)
{
        struct acpi_table_header *table;
        struct acpi_pptt_cache *found_cache;
        acpi_status status;
        u32 acpi_cpu_id = get_acpi_id_for_cpu(cpu);
        struct acpi_pptt_processor *cpu_node = NULL;
        int ret = -1;

        status = acpi_get_table(ACPI_SIG_PPTT, 0, &table);
        if (ACPI_FAILURE(status)) {
                acpi_pptt_warn_missing();
                return -ENOENT;
        }

        found_cache = acpi_find_cache_node(table, acpi_cpu_id,
                                           CACHE_TYPE_UNIFIED,
                                           level,
                                           &cpu_node);
        if (found_cache)
                ret = ACPI_PTR_DIFF(cpu_node, table);

        acpi_put_table(table);

        return ret;
}


/**
 * find_acpi_cpu_topology_package() - Determine a unique CPU package value
 * @cpu: Kernel logical CPU number
 *
 * Determine a topology unique package ID for the given CPU.
 * This ID can then be used to group peers, which will have matching ids.
 *
 * The search terminates when either a level is found with the PHYSICAL_PACKAGE
 * flag set or we reach a root node.
 *
 * Return: -ENOENT if the PPTT doesn't exist, or the CPU cannot be found.
 * Otherwise returns a value which represents the package for this CPU.
 */
int find_acpi_cpu_topology_package(unsigned int cpu)
{
        return find_acpi_cpu_topology_tag(cpu, PPTT_ABORT_PACKAGE,
                                          ACPI_PPTT_PHYSICAL_PACKAGE);
}

/**
 * find_acpi_cpu_topology_hetero_id() - Get a core architecture tag
 * @cpu: Kernel logical CPU number
 *
 * Determine a unique heterogeneous tag for the given CPU. CPUs with the same
 * implementation should have matching tags.
 *
 * The returned tag can be used to group peers with identical implementation.
 *
 * The search terminates when a level is found with the identical implementation
 * flag set or we reach a root node.
 *
 * Due to limitations in the PPTT data structure, there may be rare situations
 * where two cores in a heterogeneous machine may be identical, but won't have
 * the same tag.
 *
 * Return: -ENOENT if the PPTT doesn't exist, or the CPU cannot be found.
 * Otherwise returns a value which represents a group of identical cores
 * similar to this CPU.
 */
int find_acpi_cpu_topology_hetero_id(unsigned int cpu)
{
        return find_acpi_cpu_topology_tag(cpu, PPTT_ABORT_PACKAGE,
                                          ACPI_PPTT_ACPI_IDENTICAL);
}