/*

   * Direct MTD block device access
   *

   * Copyright © 1999-2010 David Woodhouse <dwmw2@infradead.org>
   * Copyright © 2000-2003 Nicolas Pitre <nico@fluxnic.net>
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
   *

   */

  #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>

  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;

  };

  static DEFINE_MUTEX(mtdblks_lock);

  /*
   * 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 void erase_callback(struct erase_info *done)
  {
  	wait_queue_head_t *wait_q = (wait_queue_head_t *)done->priv;
  	wake_up(wait_q);
  }

  static int erase_write (struct mtd_info *mtd, unsigned long pos,

  			int len, const char *buf)
  {
  	struct erase_info erase;
  	DECLARE_WAITQUEUE(wait, current);
  	wait_queue_head_t wait_q;
  	size_t retlen;
  	int ret;
  
  	/*
  	 * First, let's erase the flash block.
  	 */
  
  	init_waitqueue_head(&wait_q);
  	erase.mtd = mtd;
  	erase.callback = erase_callback;
  	erase.addr = pos;
  	erase.len = len;
  	erase.priv = (u_long)&wait_q;
  
  	set_current_state(TASK_INTERRUPTIBLE);
  	add_wait_queue(&wait_q, &wait);

  	ret = mtd_erase(mtd, &erase);

  	if (ret) {
  		set_current_state(TASK_RUNNING);
  		remove_wait_queue(&wait_q, &wait);
  		printk (KERN_WARNING "mtdblock: erase of region [0x%lx, 0x%x] "
  				     "on \"%s\" failed
  ",
  			pos, len, mtd->name);
  		return ret;
  	}
  
  	schedule();  /* Wait for erase to finish. */
  	remove_wait_queue(&wait_q, &wait);
  
  	/*

  	 * 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
  ", mtd->name,

  			mtdblk->cache_offset, mtdblk->cache_size);

  
  	ret = erase_write (mtd, mtdblk->cache_offset,

  			   mtdblk->cache_size, mtdblk->cache_data);
  	if (ret)
  		return ret;
  
  	/*

  	 * 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.
  	 */
  	mtdblk->cache_state = STATE_EMPTY;
  	return 0;
  }

  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
  ",

  		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
  ",

  			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
  ");

  	mutex_lock(&mtdblks_lock);

  	if (mtdblk->count) {
  		mtdblk->count++;

  		mutex_unlock(&mtdblks_lock);

  		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;
  	}

  	mutex_unlock(&mtdblks_lock);

  	pr_debug("ok
  ");

  
  	return 0;
  }
  
  static int mtdblock_release(struct mtd_blktrans_dev *mbd)
  {

  	struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd);

  	pr_debug("mtdblock_release
  ");

  	mutex_lock(&mtdblks_lock);

  	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 */

  		mtd_sync(mbd->mtd);

  		vfree(mtdblk->cache_data);

  	}

  
  	mutex_unlock(&mtdblks_lock);

  	pr_debug("ok
  ");

  
  	return 0;

  }

  
  static int mtdblock_flush(struct mtd_blktrans_dev *dev)
  {

  	struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);

  	mutex_lock(&mtdblk->cache_mutex);

  	write_cached_data(mtdblk);

  	mutex_unlock(&mtdblk->cache_mutex);

  	mtd_sync(dev->mtd);

  	return 0;
  }
  
  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 (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		= 31,
  	.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,
  };
  
  static int __init init_mtdblock(void)
  {
  	return register_mtd_blktrans(&mtdblock_tr);
  }
  
  static void __exit cleanup_mtdblock(void)
  {
  	deregister_mtd_blktrans(&mtdblock_tr);
  }
  
  module_init(init_mtdblock);
  module_exit(cleanup_mtdblock);
  
  
  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");