// SPDX-License-Identifier: GPL-2.0-only
#include <linux/module.h>
#include <linux/scatterlist.h>
#include <linux/mempool.h>
#include <linux/slab.h>

#define SG_MEMPOOL_NR           ARRAY_SIZE(sg_pools)
#define SG_MEMPOOL_SIZE         2

struct sg_pool {
        size_t          size;
        char            *name;
        struct kmem_cache       *slab;
        mempool_t       *pool;
};

#define SP(x) { .size = x, "sgpool-" __stringify(x) }
#if (SG_CHUNK_SIZE < 32)
#error SG_CHUNK_SIZE is too small (must be 32 or greater)
#endif
static struct sg_pool sg_pools[] = {
        SP(8),
        SP(16),
#if (SG_CHUNK_SIZE > 32)
        SP(32),
#if (SG_CHUNK_SIZE > 64)
        SP(64),
#if (SG_CHUNK_SIZE > 128)
        SP(128),
#if (SG_CHUNK_SIZE > 256)
#error SG_CHUNK_SIZE is too large (256 MAX)
#endif
#endif
#endif
#endif
        SP(SG_CHUNK_SIZE)
};
#undef SP

static inline unsigned int sg_pool_index(unsigned short nents)
{
        unsigned int index;

        BUG_ON(nents > SG_CHUNK_SIZE);

        if (nents <= 8)
                index = 0;
        else
                index = get_count_order(nents) - 3;

        return index;
}

static void sg_pool_free(struct scatterlist *sgl, unsigned int nents)
{
        struct sg_pool *sgp;

        sgp = sg_pools + sg_pool_index(nents);
        mempool_free(sgl, sgp->pool);
}

static struct scatterlist *sg_pool_alloc(unsigned int nents, gfp_t gfp_mask)
{
        struct sg_pool *sgp;

        sgp = sg_pools + sg_pool_index(nents);
        return mempool_alloc(sgp->pool, gfp_mask);
}

/**
 * sg_free_table_chained - Free a previously mapped sg table
 * @table:      The sg table header to use
 * @nents_first_chunk: size of the first_chunk SGL passed to
 *              sg_alloc_table_chained
 *
 *  Description:
 *    Free an sg table previously allocated and setup with
 *    sg_alloc_table_chained().
 *
 *    @nents_first_chunk has to be same with that same parameter passed
 *    to sg_alloc_table_chained().
 *
 **/
void sg_free_table_chained(struct sg_table *table,
                unsigned nents_first_chunk)
{
        if (table->orig_nents <= nents_first_chunk)
                return;

        if (nents_first_chunk == 1)
                nents_first_chunk = 0;

        __sg_free_table(table, SG_CHUNK_SIZE, nents_first_chunk, sg_pool_free,
                        table->orig_nents);
}
EXPORT_SYMBOL_GPL(sg_free_table_chained);

/**
 * sg_alloc_table_chained - Allocate and chain SGLs in an sg table
 * @table:      The sg table header to use
 * @nents:      Number of entries in sg list
 * @first_chunk: first SGL
 * @nents_first_chunk: number of the SGL of @first_chunk
 *
 *  Description:
 *    Allocate and chain SGLs in an sg table. If @nents@ is larger than
 *    @nents_first_chunk a chained sg table will be setup. @first_chunk is
 *    ignored if nents_first_chunk <= 1 because user expects the SGL points
 *    non-chain SGL.
 *
 **/
int sg_alloc_table_chained(struct sg_table *table, int nents,
                struct scatterlist *first_chunk, unsigned nents_first_chunk)
{
        int ret;

        BUG_ON(!nents);

        if (first_chunk && nents_first_chunk) {
                if (nents <= nents_first_chunk) {
                        table->nents = table->orig_nents = nents;
                        sg_init_table(table->sgl, nents);
                        return 0;
                }
        }

        /* User supposes that the 1st SGL includes real entry */
        if (nents_first_chunk <= 1) {
                first_chunk = NULL;
                nents_first_chunk = 0;
        }

        ret = __sg_alloc_table(table, nents, SG_CHUNK_SIZE,
                               first_chunk, nents_first_chunk,
                               GFP_ATOMIC, sg_pool_alloc);
        if (unlikely(ret))
                sg_free_table_chained(table, nents_first_chunk);
        return ret;
}
EXPORT_SYMBOL_GPL(sg_alloc_table_chained);

static __init int sg_pool_init(void)
{
        int i;

        for (i = 0; i < SG_MEMPOOL_NR; i++) {
                struct sg_pool *sgp = sg_pools + i;
                int size = sgp->size * sizeof(struct scatterlist);

                sgp->slab = kmem_cache_create(sgp->name, size, 0,
                                SLAB_HWCACHE_ALIGN, NULL);
                if (!sgp->slab) {
                        printk(KERN_ERR "SG_POOL: can't init sg slab %s\n",
                                        sgp->name);
                        goto cleanup_sdb;
                }

                sgp->pool = mempool_create_slab_pool(SG_MEMPOOL_SIZE,
                                                     sgp->slab);
                if (!sgp->pool) {
                        printk(KERN_ERR "SG_POOL: can't init sg mempool %s\n",
                                        sgp->name);
                        goto cleanup_sdb;
                }
        }

        return 0;

cleanup_sdb:
        for (i = 0; i < SG_MEMPOOL_NR; i++) {
                struct sg_pool *sgp = sg_pools + i;

                mempool_destroy(sgp->pool);
                kmem_cache_destroy(sgp->slab);
        }

        return -ENOMEM;
}

static __exit void sg_pool_exit(void)
{
        int i;

        for (i = 0; i < SG_MEMPOOL_NR; i++) {
                struct sg_pool *sgp = sg_pools + i;
                mempool_destroy(sgp->pool);
                kmem_cache_destroy(sgp->slab);
        }
}

module_init(sg_pool_init);
module_exit(sg_pool_exit);