// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Direct MTD block device access
 *
 * Copyright © 1999-2010 David Woodhouse <dwmw2@infradead.org>
 * Copyright © 2000-2003 Nicolas Pitre <nico@fluxnic.net>
 */

#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/vmalloc.h>

#include <linux/mtd/mtd.h>
#include <linux/mtd/blktrans.h>
#include <linux/mutex.h>
#include <linux/major.h>


struct mtdblk_dev {
        struct mtd_blktrans_dev mbd;
        int count;
        struct mutex cache_mutex;
        unsigned char *cache_data;
        unsigned long cache_offset;
        unsigned int cache_size;
        enum { STATE_EMPTY, STATE_CLEAN, STATE_DIRTY } cache_state;
};

/*
 * Cache stuff...
 *
 * Since typical flash erasable sectors are much larger than what Linux's
 * buffer cache can handle, we must implement read-modify-write on flash
 * sectors for each block write requests.  To avoid over-erasing flash sectors
 * and to speed things up, we locally cache a whole flash sector while it is
 * being written to until a different sector is required.
 */

static int erase_write (struct mtd_info *mtd, unsigned long pos,
                        unsigned int len, const char *buf)
{
        struct erase_info erase;
        size_t retlen;
        int ret;

        /*
         * First, let's erase the flash block.
         */
        erase.addr = pos;
        erase.len = len;

        ret = mtd_erase(mtd, &erase);
        if (ret) {
                printk (KERN_WARNING "mtdblock: erase of region [0x%lx, 0x%x] "
                                     "on \"%s\" failed\n",
                        pos, len, mtd->name);
                return ret;
        }

        /*
         * Next, write the data to flash.
         */

        ret = mtd_write(mtd, pos, len, &retlen, buf);
        if (ret)
                return ret;
        if (retlen != len)
                return -EIO;
        return 0;
}


static int write_cached_data (struct mtdblk_dev *mtdblk)
{
        struct mtd_info *mtd = mtdblk->mbd.mtd;
        int ret;

        if (mtdblk->cache_state != STATE_DIRTY)
                return 0;

        pr_debug("mtdblock: writing cached data for \"%s\" "
                        "at 0x%lx, size 0x%x\n", mtd->name,
                        mtdblk->cache_offset, mtdblk->cache_size);

        ret = erase_write (mtd, mtdblk->cache_offset,
                           mtdblk->cache_size, mtdblk->cache_data);

        /*
         * Here we could arguably set the cache state to STATE_CLEAN.
         * However this could lead to inconsistency since we will not
         * be notified if this content is altered on the flash by other
         * means.  Let's declare it empty and leave buffering tasks to
         * the buffer cache instead.
         *
         * If this cache_offset points to a bad block, data cannot be
         * written to the device. Clear cache_state to avoid writing to
         * bad blocks repeatedly.
         */
        if (ret == 0 || ret == -EIO)
                mtdblk->cache_state = STATE_EMPTY;
        return ret;
}


static int do_cached_write (struct mtdblk_dev *mtdblk, unsigned long pos,
                            int len, const char *buf)
{
        struct mtd_info *mtd = mtdblk->mbd.mtd;
        unsigned int sect_size = mtdblk->cache_size;
        size_t retlen;
        int ret;

        pr_debug("mtdblock: write on \"%s\" at 0x%lx, size 0x%x\n",
                mtd->name, pos, len);

        if (!sect_size)
                return mtd_write(mtd, pos, len, &retlen, buf);

        while (len > 0) {
                unsigned long sect_start = (pos/sect_size)*sect_size;
                unsigned int offset = pos - sect_start;
                unsigned int size = sect_size - offset;
                if( size > len )
                        size = len;

                if (size == sect_size) {
                        /*
                         * We are covering a whole sector.  Thus there is no
                         * need to bother with the cache while it may still be
                         * useful for other partial writes.
                         */
                        ret = erase_write (mtd, pos, size, buf);
                        if (ret)
                                return ret;
                } else {
                        /* Partial sector: need to use the cache */

                        if (mtdblk->cache_state == STATE_DIRTY &&
                            mtdblk->cache_offset != sect_start) {
                                ret = write_cached_data(mtdblk);
                                if (ret)
                                        return ret;
                        }

                        if (mtdblk->cache_state == STATE_EMPTY ||
                            mtdblk->cache_offset != sect_start) {
                                /* fill the cache with the current sector */
                                mtdblk->cache_state = STATE_EMPTY;
                                ret = mtd_read(mtd, sect_start, sect_size,
                                               &retlen, mtdblk->cache_data);
                                if (ret)
                                        return ret;
                                if (retlen != sect_size)
                                        return -EIO;

                                mtdblk->cache_offset = sect_start;
                                mtdblk->cache_size = sect_size;
                                mtdblk->cache_state = STATE_CLEAN;
                        }

                        /* write data to our local cache */
                        memcpy (mtdblk->cache_data + offset, buf, size);
                        mtdblk->cache_state = STATE_DIRTY;
                }

                buf += size;
                pos += size;
                len -= size;
        }

        return 0;
}


static int do_cached_read (struct mtdblk_dev *mtdblk, unsigned long pos,
                           int len, char *buf)
{
        struct mtd_info *mtd = mtdblk->mbd.mtd;
        unsigned int sect_size = mtdblk->cache_size;
        size_t retlen;
        int ret;

        pr_debug("mtdblock: read on \"%s\" at 0x%lx, size 0x%x\n",
                        mtd->name, pos, len);

        if (!sect_size)
                return mtd_read(mtd, pos, len, &retlen, buf);

        while (len > 0) {
                unsigned long sect_start = (pos/sect_size)*sect_size;
                unsigned int offset = pos - sect_start;
                unsigned int size = sect_size - offset;
                if (size > len)
                        size = len;

                /*
                 * Check if the requested data is already cached
                 * Read the requested amount of data from our internal cache if it
                 * contains what we want, otherwise we read the data directly
                 * from flash.
                 */
                if (mtdblk->cache_state != STATE_EMPTY &&
                    mtdblk->cache_offset == sect_start) {
                        memcpy (buf, mtdblk->cache_data + offset, size);
                } else {
                        ret = mtd_read(mtd, pos, size, &retlen, buf);
                        if (ret)
                                return ret;
                        if (retlen != size)
                                return -EIO;
                }

                buf += size;
                pos += size;
                len -= size;
        }

        return 0;
}

static int mtdblock_readsect(struct mtd_blktrans_dev *dev,
                              unsigned long block, char *buf)
{
        struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);
        return do_cached_read(mtdblk, block<<9, 512, buf);
}

static int mtdblock_writesect(struct mtd_blktrans_dev *dev,
                              unsigned long block, char *buf)
{
        struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);
        if (unlikely(!mtdblk->cache_data && mtdblk->cache_size)) {
                mtdblk->cache_data = vmalloc(mtdblk->mbd.mtd->erasesize);
                if (!mtdblk->cache_data)
                        return -EINTR;
                /* -EINTR is not really correct, but it is the best match
                 * documented in man 2 write for all cases.  We could also
                 * return -EAGAIN sometimes, but why bother?
                 */
        }
        return do_cached_write(mtdblk, block<<9, 512, buf);
}

static int mtdblock_open(struct mtd_blktrans_dev *mbd)
{
        struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd);

        pr_debug("mtdblock_open\n");

        if (mtdblk->count) {
                mtdblk->count++;
                return 0;
        }

        /* OK, it's not open. Create cache info for it */
        mtdblk->count = 1;
        mutex_init(&mtdblk->cache_mutex);
        mtdblk->cache_state = STATE_EMPTY;
        if (!(mbd->mtd->flags & MTD_NO_ERASE) && mbd->mtd->erasesize) {
                mtdblk->cache_size = mbd->mtd->erasesize;
                mtdblk->cache_data = NULL;
        }

        pr_debug("ok\n");

        return 0;
}

static void mtdblock_release(struct mtd_blktrans_dev *mbd)
{
        struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd);

        pr_debug("mtdblock_release\n");

        mutex_lock(&mtdblk->cache_mutex);
        write_cached_data(mtdblk);
        mutex_unlock(&mtdblk->cache_mutex);

        if (!--mtdblk->count) {
                /*
                 * It was the last usage. Free the cache, but only sync if
                 * opened for writing.
                 */
                if (mbd->file_mode & FMODE_WRITE)
                        mtd_sync(mbd->mtd);
                vfree(mtdblk->cache_data);
        }

        pr_debug("ok\n");
}

static int mtdblock_flush(struct mtd_blktrans_dev *dev)
{
        struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);
        int ret;

        mutex_lock(&mtdblk->cache_mutex);
        ret = write_cached_data(mtdblk);
        mutex_unlock(&mtdblk->cache_mutex);
        mtd_sync(dev->mtd);
        return ret;
}

static void mtdblock_add_mtd(struct mtd_blktrans_ops *tr, struct mtd_info *mtd)
{
        struct mtdblk_dev *dev = kzalloc(sizeof(*dev), GFP_KERNEL);

        if (!dev)
                return;

        dev->mbd.mtd = mtd;
        dev->mbd.devnum = mtd->index;

        dev->mbd.size = mtd->size >> 9;
        dev->mbd.tr = tr;

        if (!(mtd->flags & MTD_WRITEABLE))
                dev->mbd.readonly = 1;

        if (mtd_type_is_nand(mtd))
                pr_warn("%s: MTD device '%s' is NAND, please consider using UBI block devices instead.\n",
                        tr->name, mtd->name);

        if (add_mtd_blktrans_dev(&dev->mbd))
                kfree(dev);
}

static void mtdblock_remove_dev(struct mtd_blktrans_dev *dev)
{
        del_mtd_blktrans_dev(dev);
}

static struct mtd_blktrans_ops mtdblock_tr = {
        .name           = "mtdblock",
        .major          = MTD_BLOCK_MAJOR,
        .part_bits      = 0,
        .blksize        = 512,
        .open           = mtdblock_open,
        .flush          = mtdblock_flush,
        .release        = mtdblock_release,
        .readsect       = mtdblock_readsect,
        .writesect      = mtdblock_writesect,
        .add_mtd        = mtdblock_add_mtd,
        .remove_dev     = mtdblock_remove_dev,
        .owner          = THIS_MODULE,
};

module_mtd_blktrans(mtdblock_tr);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Nicolas Pitre <nico@fluxnic.net> et al.");
MODULE_DESCRIPTION("Caching read/erase/writeback block device emulation access to MTD devices");