// SPDX-License-Identifier: GPL-2.0-only

#define pr_fmt(fmt)     "rtas-work-area: " fmt

#include <linux/genalloc.h>
#include <linux/log2.h>
#include <linux/kernel.h>
#include <linux/memblock.h>
#include <linux/mempool.h>
#include <linux/minmax.h>
#include <linux/mutex.h>
#include <linux/numa.h>
#include <linux/sizes.h>
#include <linux/wait.h>

#include <asm/machdep.h>
#include <asm/rtas-work-area.h>
#include <asm/rtas.h>

enum {
        /*
         * Ensure the pool is page-aligned.
         */
        RTAS_WORK_AREA_ARENA_ALIGN = PAGE_SIZE,
        /*
         * Don't let a single allocation claim the whole arena.
         */
        RTAS_WORK_AREA_ARENA_SZ = RTAS_WORK_AREA_MAX_ALLOC_SZ * 2,
        /*
         * The smallest known work area size is for ibm,get-vpd's
         * location code argument, which is limited to 79 characters
         * plus 1 nul terminator.
         *
         * PAPR+ 7.3.20 ibm,get-vpd RTAS Call
         * PAPR+ 12.3.2.4 Converged Location Code Rules - Length Restrictions
         */
        RTAS_WORK_AREA_MIN_ALLOC_SZ = roundup_pow_of_two(80),
};

static struct {
        struct gen_pool *gen_pool;
        char *arena;
        struct mutex mutex; /* serializes allocations */
        struct wait_queue_head wqh;
        mempool_t descriptor_pool;
        bool available;
} rwa_state = {
        .mutex = __MUTEX_INITIALIZER(rwa_state.mutex),
        .wqh = __WAIT_QUEUE_HEAD_INITIALIZER(rwa_state.wqh),
};

/*
 * A single work area buffer and descriptor to serve requests early in
 * boot before the allocator is fully initialized. We know 4KB is the
 * most any boot time user needs (they all call ibm,get-system-parameter).
 */
static bool early_work_area_in_use __initdata;
static char early_work_area_buf[SZ_4K] __initdata __aligned(SZ_4K);
static struct rtas_work_area early_work_area __initdata = {
        .buf = early_work_area_buf,
        .size = sizeof(early_work_area_buf),
};


static struct rtas_work_area * __init rtas_work_area_alloc_early(size_t size)
{
        WARN_ON(size > early_work_area.size);
        WARN_ON(early_work_area_in_use);
        early_work_area_in_use = true;
        memset(early_work_area.buf, 0, early_work_area.size);
        return &early_work_area;
}

static void __init rtas_work_area_free_early(struct rtas_work_area *work_area)
{
        WARN_ON(work_area != &early_work_area);
        WARN_ON(!early_work_area_in_use);
        early_work_area_in_use = false;
}

struct rtas_work_area * __ref __rtas_work_area_alloc(size_t size)
{
        struct rtas_work_area *area;
        unsigned long addr;

        might_sleep();

        /*
         * The rtas_work_area_alloc() wrapper enforces this at build
         * time. Requests that exceed the arena size will block
         * indefinitely.
         */
        WARN_ON(size > RTAS_WORK_AREA_MAX_ALLOC_SZ);

        if (!rwa_state.available)
                return rtas_work_area_alloc_early(size);
        /*
         * To ensure FCFS behavior and prevent a high rate of smaller
         * requests from starving larger ones, use the mutex to queue
         * allocations.
         */
        mutex_lock(&rwa_state.mutex);
        wait_event(rwa_state.wqh,
                   (addr = gen_pool_alloc(rwa_state.gen_pool, size)) != 0);
        mutex_unlock(&rwa_state.mutex);

        area = mempool_alloc(&rwa_state.descriptor_pool, GFP_KERNEL);
        area->buf = (char *)addr;
        area->size = size;

        return area;
}

void __ref rtas_work_area_free(struct rtas_work_area *area)
{
        if (!rwa_state.available) {
                rtas_work_area_free_early(area);
                return;
        }

        gen_pool_free(rwa_state.gen_pool, (unsigned long)area->buf, area->size);
        mempool_free(area, &rwa_state.descriptor_pool);
        wake_up(&rwa_state.wqh);
}

/*
 * Initialization of the work area allocator happens in two parts. To
 * reliably reserve an arena that satisfies RTAS addressing
 * requirements, we must perform a memblock allocation early,
 * immmediately after RTAS instantiation. Then we have to wait until
 * the slab allocator is up before setting up the descriptor mempool
 * and adding the arena to a gen_pool.
 */
static __init int rtas_work_area_allocator_init(void)
{
        const unsigned int order = ilog2(RTAS_WORK_AREA_MIN_ALLOC_SZ);
        const phys_addr_t pa_start = __pa(rwa_state.arena);
        const phys_addr_t pa_end = pa_start + RTAS_WORK_AREA_ARENA_SZ - 1;
        struct gen_pool *pool;
        const int nid = NUMA_NO_NODE;
        int err;

        err = -ENOMEM;
        if (!rwa_state.arena)
                goto err_out;

        pool = gen_pool_create(order, nid);
        if (!pool)
                goto err_out;
        /*
         * All RTAS functions that consume work areas are OK with
         * natural alignment, when they have alignment requirements at
         * all.
         */
        gen_pool_set_algo(pool, gen_pool_first_fit_order_align, NULL);

        err = gen_pool_add(pool, (unsigned long)rwa_state.arena,
                           RTAS_WORK_AREA_ARENA_SZ, nid);
        if (err)
                goto err_destroy;

        err = mempool_init_kmalloc_pool(&rwa_state.descriptor_pool, 1,
                                        sizeof(struct rtas_work_area));
        if (err)
                goto err_destroy;

        rwa_state.gen_pool = pool;
        rwa_state.available = true;

        pr_debug("arena [%pa-%pa] (%uK), min/max alloc sizes %u/%u\n",
                 &pa_start, &pa_end,
                 RTAS_WORK_AREA_ARENA_SZ / SZ_1K,
                 RTAS_WORK_AREA_MIN_ALLOC_SZ,
                 RTAS_WORK_AREA_MAX_ALLOC_SZ);

        return 0;

err_destroy:
        gen_pool_destroy(pool);
err_out:
        return err;
}
machine_arch_initcall(pseries, rtas_work_area_allocator_init);

/**
 * rtas_work_area_reserve_arena() - Reserve memory suitable for RTAS work areas.
 * @limit: Upper limit for memblock allocation.
 */
void __init rtas_work_area_reserve_arena(const phys_addr_t limit)
{
        const phys_addr_t align = RTAS_WORK_AREA_ARENA_ALIGN;
        const phys_addr_t size = RTAS_WORK_AREA_ARENA_SZ;
        const phys_addr_t min = MEMBLOCK_LOW_LIMIT;
        const int nid = NUMA_NO_NODE;

        /*
         * Too early for a machine_is(pseries) check. But PAPR
         * effectively mandates that ibm,get-system-parameter is
         * present:
         *
         * R1–7.3.16–1. All platforms must support the System
         * Parameters option.
         *
         * So set up the arena if we find that, with a fallback to
         * ibm,configure-connector, just in case.
         */
        if (rtas_function_implemented(RTAS_FN_IBM_GET_SYSTEM_PARAMETER) ||
            rtas_function_implemented(RTAS_FN_IBM_CONFIGURE_CONNECTOR))
                rwa_state.arena = memblock_alloc_try_nid(size, align, min, limit, nid);
}