/*
 * Basic general purpose allocator for managing special purpose
 * memory, for example, memory that is not managed by the regular
 * kmalloc/kfree interface.  Uses for this includes on-device special
 * memory, uncached memory etc.
 *
 * It is safe to use the allocator in NMI handlers and other special
 * unblockable contexts that could otherwise deadlock on locks.  This
 * is implemented by using atomic operations and retries on any
 * conflicts.  The disadvantage is that there may be livelocks in
 * extreme cases.  For better scalability, one allocator can be used
 * for each CPU.
 *
 * The lockless operation only works if there is enough memory
 * available.  If new memory is added to the pool a lock has to be
 * still taken.  So any user relying on locklessness has to ensure
 * that sufficient memory is preallocated.
 *
 * The basic atomic operation of this allocator is cmpxchg on long.
 * On architectures that don't have NMI-safe cmpxchg implementation,
 * the allocator can NOT be used in NMI handler.  So code uses the
 * allocator in NMI handler should depend on
 * CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
 *
 * Copyright 2005 (C) Jes Sorensen <jes@trained-monkey.org>
 *
 * This source code is licensed under the GNU General Public License,
 * Version 2.  See the file COPYING for more details.
 */

#include <linux/slab.h>
#include <linux/module.h>
#include <linux/bitmap.h>
#include <linux/rculist.h>
#include <linux/interrupt.h>
#include <linux/genalloc.h>

static int set_bits_ll(unsigned long *addr, unsigned long mask_to_set)
{
        unsigned long val, nval;

        nval = *addr;
        do {
                val = nval;
                if (val & mask_to_set)
                        return -EBUSY;
                cpu_relax();
        } while ((nval = cmpxchg(addr, val, val | mask_to_set)) != val);

        return 0;
}

static int clear_bits_ll(unsigned long *addr, unsigned long mask_to_clear)
{
        unsigned long val, nval;

        nval = *addr;
        do {
                val = nval;
                if ((val & mask_to_clear) != mask_to_clear)
                        return -EBUSY;
                cpu_relax();
        } while ((nval = cmpxchg(addr, val, val & ~mask_to_clear)) != val);

        return 0;
}

/*
 * bitmap_set_ll - set the specified number of bits at the specified position
 * @map: pointer to a bitmap
 * @start: a bit position in @map
 * @nr: number of bits to set
 *
 * Set @nr bits start from @start in @map lock-lessly. Several users
 * can set/clear the same bitmap simultaneously without lock. If two
 * users set the same bit, one user will return remain bits, otherwise
 * return 0.
 */
static int bitmap_set_ll(unsigned long *map, int start, int nr)
{
        unsigned long *p = map + BIT_WORD(start);
        const int size = start + nr;
        int bits_to_set = BITS_PER_LONG - (start % BITS_PER_LONG);
        unsigned long mask_to_set = BITMAP_FIRST_WORD_MASK(start);

        while (nr - bits_to_set >= 0) {
                if (set_bits_ll(p, mask_to_set))
                        return nr;
                nr -= bits_to_set;
                bits_to_set = BITS_PER_LONG;
                mask_to_set = ~0UL;
                p++;
        }
        if (nr) {
                mask_to_set &= BITMAP_LAST_WORD_MASK(size);
                if (set_bits_ll(p, mask_to_set))
                        return nr;
        }

        return 0;
}

/*
 * bitmap_clear_ll - clear the specified number of bits at the specified position
 * @map: pointer to a bitmap
 * @start: a bit position in @map
 * @nr: number of bits to set
 *
 * Clear @nr bits start from @start in @map lock-lessly. Several users
 * can set/clear the same bitmap simultaneously without lock. If two
 * users clear the same bit, one user will return remain bits,
 * otherwise return 0.
 */
static int bitmap_clear_ll(unsigned long *map, int start, int nr)
{
        unsigned long *p = map + BIT_WORD(start);
        const int size = start + nr;
        int bits_to_clear = BITS_PER_LONG - (start % BITS_PER_LONG);
        unsigned long mask_to_clear = BITMAP_FIRST_WORD_MASK(start);

        while (nr - bits_to_clear >= 0) {
                if (clear_bits_ll(p, mask_to_clear))
                        return nr;
                nr -= bits_to_clear;
                bits_to_clear = BITS_PER_LONG;
                mask_to_clear = ~0UL;
                p++;
        }
        if (nr) {
                mask_to_clear &= BITMAP_LAST_WORD_MASK(size);
                if (clear_bits_ll(p, mask_to_clear))
                        return nr;
        }

        return 0;
}

/**
 * gen_pool_create - create a new special memory pool
 * @min_alloc_order: log base 2 of number of bytes each bitmap bit represents
 * @nid: node id of the node the pool structure should be allocated on, or -1
 *
 * Create a new special memory pool that can be used to manage special purpose
 * memory not managed by the regular kmalloc/kfree interface.
 */
struct gen_pool *gen_pool_create(int min_alloc_order, int nid)
{
        struct gen_pool *pool;

        pool = kmalloc_node(sizeof(struct gen_pool), GFP_KERNEL, nid);
        if (pool != NULL) {
                spin_lock_init(&pool->lock);
                INIT_LIST_HEAD(&pool->chunks);
                pool->min_alloc_order = min_alloc_order;
        }
        return pool;
}
EXPORT_SYMBOL(gen_pool_create);

/**
 * gen_pool_add_virt - add a new chunk of special memory to the pool
 * @pool: pool to add new memory chunk to
 * @virt: virtual starting address of memory chunk to add to pool
 * @phys: physical starting address of memory chunk to add to pool
 * @size: size in bytes of the memory chunk to add to pool
 * @nid: node id of the node the chunk structure and bitmap should be
 *       allocated on, or -1
 *
 * Add a new chunk of special memory to the specified pool.
 *
 * Returns 0 on success or a -ve errno on failure.
 */
int gen_pool_add_virt(struct gen_pool *pool, unsigned long virt, phys_addr_t phys,
                 size_t size, int nid)
{
        struct gen_pool_chunk *chunk;
        int nbits = size >> pool->min_alloc_order;
        int nbytes = sizeof(struct gen_pool_chunk) +
                                (nbits + BITS_PER_BYTE - 1) / BITS_PER_BYTE;

        chunk = kmalloc_node(nbytes, GFP_KERNEL | __GFP_ZERO, nid);
        if (unlikely(chunk == NULL))
                return -ENOMEM;

        chunk->phys_addr = phys;
        chunk->start_addr = virt;
        chunk->end_addr = virt + size;
        atomic_set(&chunk->avail, size);

        spin_lock(&pool->lock);
        list_add_rcu(&chunk->next_chunk, &pool->chunks);
        spin_unlock(&pool->lock);

        return 0;
}
EXPORT_SYMBOL(gen_pool_add_virt);

/**
 * gen_pool_virt_to_phys - return the physical address of memory
 * @pool: pool to allocate from
 * @addr: starting address of memory
 *
 * Returns the physical address on success, or -1 on error.
 */
phys_addr_t gen_pool_virt_to_phys(struct gen_pool *pool, unsigned long addr)
{
        struct gen_pool_chunk *chunk;
        phys_addr_t paddr = -1;

        rcu_read_lock();
        list_for_each_entry_rcu(chunk, &pool->chunks, next_chunk) {
                if (addr >= chunk->start_addr && addr < chunk->end_addr) {
                        paddr = chunk->phys_addr + (addr - chunk->start_addr);
                        break;
                }
        }
        rcu_read_unlock();

        return paddr;
}
EXPORT_SYMBOL(gen_pool_virt_to_phys);

/**
 * gen_pool_destroy - destroy a special memory pool
 * @pool: pool to destroy
 *
 * Destroy the specified special memory pool. Verifies that there are no
 * outstanding allocations.
 */
void gen_pool_destroy(struct gen_pool *pool)
{
        struct list_head *_chunk, *_next_chunk;
        struct gen_pool_chunk *chunk;
        int order = pool->min_alloc_order;
        int bit, end_bit;

        list_for_each_safe(_chunk, _next_chunk, &pool->chunks) {
                chunk = list_entry(_chunk, struct gen_pool_chunk, next_chunk);
                list_del(&chunk->next_chunk);

                end_bit = (chunk->end_addr - chunk->start_addr) >> order;
                bit = find_next_bit(chunk->bits, end_bit, 0);
                BUG_ON(bit < end_bit);

                kfree(chunk);
        }
        kfree(pool);
        return;
}
EXPORT_SYMBOL(gen_pool_destroy);

/**
 * gen_pool_alloc - allocate special memory from the pool
 * @pool: pool to allocate from
 * @size: number of bytes to allocate from the pool
 *
 * Allocate the requested number of bytes from the specified pool.
 * Uses a first-fit algorithm. Can not be used in NMI handler on
 * architectures without NMI-safe cmpxchg implementation.
 */
unsigned long gen_pool_alloc(struct gen_pool *pool, size_t size)
{
        struct gen_pool_chunk *chunk;
        unsigned long addr = 0;
        int order = pool->min_alloc_order;
        int nbits, start_bit = 0, end_bit, remain;

#ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
        BUG_ON(in_nmi());
#endif

        if (size == 0)
                return 0;

        nbits = (size + (1UL << order) - 1) >> order;
        rcu_read_lock();
        list_for_each_entry_rcu(chunk, &pool->chunks, next_chunk) {
                if (size > atomic_read(&chunk->avail))
                        continue;

                end_bit = (chunk->end_addr - chunk->start_addr) >> order;
retry:
                start_bit = bitmap_find_next_zero_area(chunk->bits, end_bit,
                                                       start_bit, nbits, 0);
                if (start_bit >= end_bit)
                        continue;
                remain = bitmap_set_ll(chunk->bits, start_bit, nbits);
                if (remain) {
                        remain = bitmap_clear_ll(chunk->bits, start_bit,
                                                 nbits - remain);
                        BUG_ON(remain);
                        goto retry;
                }

                addr = chunk->start_addr + ((unsigned long)start_bit << order);
                size = nbits << order;
                atomic_sub(size, &chunk->avail);
                break;
        }
        rcu_read_unlock();
        return addr;
}
EXPORT_SYMBOL(gen_pool_alloc);

/**
 * gen_pool_free - free allocated special memory back to the pool
 * @pool: pool to free to
 * @addr: starting address of memory to free back to pool
 * @size: size in bytes of memory to free
 *
 * Free previously allocated special memory back to the specified
 * pool.  Can not be used in NMI handler on architectures without
 * NMI-safe cmpxchg implementation.
 */
void gen_pool_free(struct gen_pool *pool, unsigned long addr, size_t size)
{
        struct gen_pool_chunk *chunk;
        int order = pool->min_alloc_order;
        int start_bit, nbits, remain;

#ifndef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
        BUG_ON(in_nmi());
#endif

        nbits = (size + (1UL << order) - 1) >> order;
        rcu_read_lock();
        list_for_each_entry_rcu(chunk, &pool->chunks, next_chunk) {
                if (addr >= chunk->start_addr && addr < chunk->end_addr) {
                        BUG_ON(addr + size > chunk->end_addr);
                        start_bit = (addr - chunk->start_addr) >> order;
                        remain = bitmap_clear_ll(chunk->bits, start_bit, nbits);
                        BUG_ON(remain);
                        size = nbits << order;
                        atomic_add(size, &chunk->avail);
                        rcu_read_unlock();
                        return;
                }
        }
        rcu_read_unlock();
        BUG();
}
EXPORT_SYMBOL(gen_pool_free);

/**
 * gen_pool_for_each_chunk - call func for every chunk of generic memory pool
 * @pool:       the generic memory pool
 * @func:       func to call
 * @data:       additional data used by @func
 *
 * Call @func for every chunk of generic memory pool.  The @func is
 * called with rcu_read_lock held.
 */
void gen_pool_for_each_chunk(struct gen_pool *pool,
        void (*func)(struct gen_pool *pool, struct gen_pool_chunk *chunk, void *data),
        void *data)
{
        struct gen_pool_chunk *chunk;

        rcu_read_lock();
        list_for_each_entry_rcu(chunk, &(pool)->chunks, next_chunk)
                func(pool, chunk, data);
        rcu_read_unlock();
}
EXPORT_SYMBOL(gen_pool_for_each_chunk);

/**
 * gen_pool_avail - get available free space of the pool
 * @pool: pool to get available free space
 *
 * Return available free space of the specified pool.
 */
size_t gen_pool_avail(struct gen_pool *pool)
{
        struct gen_pool_chunk *chunk;
        size_t avail = 0;

        rcu_read_lock();
        list_for_each_entry_rcu(chunk, &pool->chunks, next_chunk)
                avail += atomic_read(&chunk->avail);
        rcu_read_unlock();
        return avail;
}
EXPORT_SYMBOL_GPL(gen_pool_avail);

/**
 * gen_pool_size - get size in bytes of memory managed by the pool
 * @pool: pool to get size
 *
 * Return size in bytes of memory managed by the pool.
 */
size_t gen_pool_size(struct gen_pool *pool)
{
        struct gen_pool_chunk *chunk;
        size_t size = 0;

        rcu_read_lock();
        list_for_each_entry_rcu(chunk, &pool->chunks, next_chunk)
                size += chunk->end_addr - chunk->start_addr;
        rcu_read_unlock();
        return size;
}
EXPORT_SYMBOL_GPL(gen_pool_size);