1 // SPDX-License-Identifier: GPL-2.0-or-later
3 * Direct MTD block device access
5 * Copyright © 1999-2010 David Woodhouse <dwmw2@infradead.org>
6 * Copyright © 2000-2003 Nicolas Pitre <nico@fluxnic.net>
10 #include <linux/init.h>
11 #include <linux/kernel.h>
12 #include <linux/module.h>
13 #include <linux/sched.h>
14 #include <linux/slab.h>
15 #include <linux/types.h>
16 #include <linux/vmalloc.h>
18 #include <linux/mtd/mtd.h>
19 #include <linux/mtd/blktrans.h>
20 #include <linux/mutex.h>
21 #include <linux/major.h>
25 struct mtd_blktrans_dev mbd;
27 struct mutex cache_mutex;
28 unsigned char *cache_data;
29 unsigned long cache_offset;
30 unsigned int cache_size;
31 enum { STATE_EMPTY, STATE_CLEAN, STATE_DIRTY } cache_state;
37 * Since typical flash erasable sectors are much larger than what Linux's
38 * buffer cache can handle, we must implement read-modify-write on flash
39 * sectors for each block write requests. To avoid over-erasing flash sectors
40 * and to speed things up, we locally cache a whole flash sector while it is
41 * being written to until a different sector is required.
44 static int erase_write (struct mtd_info *mtd, unsigned long pos,
45 unsigned int len, const char *buf)
47 struct erase_info erase;
52 * First, let's erase the flash block.
57 ret = mtd_erase(mtd, &erase);
59 printk (KERN_WARNING "mtdblock: erase of region [0x%lx, 0x%x] "
66 * Next, write the data to flash.
69 ret = mtd_write(mtd, pos, len, &retlen, buf);
78 static int write_cached_data (struct mtdblk_dev *mtdblk)
80 struct mtd_info *mtd = mtdblk->mbd.mtd;
83 if (mtdblk->cache_state != STATE_DIRTY)
86 pr_debug("mtdblock: writing cached data for \"%s\" "
87 "at 0x%lx, size 0x%x\n", mtd->name,
88 mtdblk->cache_offset, mtdblk->cache_size);
90 ret = erase_write (mtd, mtdblk->cache_offset,
91 mtdblk->cache_size, mtdblk->cache_data);
96 * Here we could arguably set the cache state to STATE_CLEAN.
97 * However this could lead to inconsistency since we will not
98 * be notified if this content is altered on the flash by other
99 * means. Let's declare it empty and leave buffering tasks to
100 * the buffer cache instead.
102 mtdblk->cache_state = STATE_EMPTY;
107 static int do_cached_write (struct mtdblk_dev *mtdblk, unsigned long pos,
108 int len, const char *buf)
110 struct mtd_info *mtd = mtdblk->mbd.mtd;
111 unsigned int sect_size = mtdblk->cache_size;
115 pr_debug("mtdblock: write on \"%s\" at 0x%lx, size 0x%x\n",
116 mtd->name, pos, len);
119 return mtd_write(mtd, pos, len, &retlen, buf);
122 unsigned long sect_start = (pos/sect_size)*sect_size;
123 unsigned int offset = pos - sect_start;
124 unsigned int size = sect_size - offset;
128 if (size == sect_size) {
130 * We are covering a whole sector. Thus there is no
131 * need to bother with the cache while it may still be
132 * useful for other partial writes.
134 ret = erase_write (mtd, pos, size, buf);
138 /* Partial sector: need to use the cache */
140 if (mtdblk->cache_state == STATE_DIRTY &&
141 mtdblk->cache_offset != sect_start) {
142 ret = write_cached_data(mtdblk);
147 if (mtdblk->cache_state == STATE_EMPTY ||
148 mtdblk->cache_offset != sect_start) {
149 /* fill the cache with the current sector */
150 mtdblk->cache_state = STATE_EMPTY;
151 ret = mtd_read(mtd, sect_start, sect_size,
152 &retlen, mtdblk->cache_data);
153 if (ret && !mtd_is_bitflip(ret))
155 if (retlen != sect_size)
158 mtdblk->cache_offset = sect_start;
159 mtdblk->cache_size = sect_size;
160 mtdblk->cache_state = STATE_CLEAN;
163 /* write data to our local cache */
164 memcpy (mtdblk->cache_data + offset, buf, size);
165 mtdblk->cache_state = STATE_DIRTY;
177 static int do_cached_read (struct mtdblk_dev *mtdblk, unsigned long pos,
180 struct mtd_info *mtd = mtdblk->mbd.mtd;
181 unsigned int sect_size = mtdblk->cache_size;
185 pr_debug("mtdblock: read on \"%s\" at 0x%lx, size 0x%x\n",
186 mtd->name, pos, len);
189 ret = mtd_read(mtd, pos, len, &retlen, buf);
190 if (ret && !mtd_is_bitflip(ret))
196 unsigned long sect_start = (pos/sect_size)*sect_size;
197 unsigned int offset = pos - sect_start;
198 unsigned int size = sect_size - offset;
203 * Check if the requested data is already cached
204 * Read the requested amount of data from our internal cache if it
205 * contains what we want, otherwise we read the data directly
208 if (mtdblk->cache_state != STATE_EMPTY &&
209 mtdblk->cache_offset == sect_start) {
210 memcpy (buf, mtdblk->cache_data + offset, size);
212 ret = mtd_read(mtd, pos, size, &retlen, buf);
213 if (ret && !mtd_is_bitflip(ret))
227 static int mtdblock_readsect(struct mtd_blktrans_dev *dev,
228 unsigned long block, char *buf)
230 struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);
231 return do_cached_read(mtdblk, block<<9, 512, buf);
234 static int mtdblock_writesect(struct mtd_blktrans_dev *dev,
235 unsigned long block, char *buf)
237 struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);
238 if (unlikely(!mtdblk->cache_data && mtdblk->cache_size)) {
239 mtdblk->cache_data = vmalloc(mtdblk->mbd.mtd->erasesize);
240 if (!mtdblk->cache_data)
242 /* -EINTR is not really correct, but it is the best match
243 * documented in man 2 write for all cases. We could also
244 * return -EAGAIN sometimes, but why bother?
247 return do_cached_write(mtdblk, block<<9, 512, buf);
250 static int mtdblock_open(struct mtd_blktrans_dev *mbd)
252 struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd);
254 pr_debug("mtdblock_open\n");
261 /* OK, it's not open. Create cache info for it */
263 mutex_init(&mtdblk->cache_mutex);
264 mtdblk->cache_state = STATE_EMPTY;
265 if (!(mbd->mtd->flags & MTD_NO_ERASE) && mbd->mtd->erasesize) {
266 mtdblk->cache_size = mbd->mtd->erasesize;
267 mtdblk->cache_data = NULL;
275 static void mtdblock_release(struct mtd_blktrans_dev *mbd)
277 struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd);
279 pr_debug("mtdblock_release\n");
281 mutex_lock(&mtdblk->cache_mutex);
282 write_cached_data(mtdblk);
283 mutex_unlock(&mtdblk->cache_mutex);
285 if (!--mtdblk->count) {
287 * It was the last usage. Free the cache, but only sync if
288 * opened for writing.
290 if (mbd->file_mode & FMODE_WRITE)
292 vfree(mtdblk->cache_data);
298 static int mtdblock_flush(struct mtd_blktrans_dev *dev)
300 struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);
302 mutex_lock(&mtdblk->cache_mutex);
303 write_cached_data(mtdblk);
304 mutex_unlock(&mtdblk->cache_mutex);
309 static void mtdblock_add_mtd(struct mtd_blktrans_ops *tr, struct mtd_info *mtd)
311 struct mtdblk_dev *dev = kzalloc(sizeof(*dev), GFP_KERNEL);
317 dev->mbd.devnum = mtd->index;
319 dev->mbd.size = mtd->size >> 9;
322 if (!(mtd->flags & MTD_WRITEABLE))
323 dev->mbd.readonly = 1;
325 if (add_mtd_blktrans_dev(&dev->mbd))
329 static void mtdblock_remove_dev(struct mtd_blktrans_dev *dev)
331 del_mtd_blktrans_dev(dev);
334 static struct mtd_blktrans_ops mtdblock_tr = {
336 .major = MTD_BLOCK_MAJOR,
339 .open = mtdblock_open,
340 .flush = mtdblock_flush,
341 .release = mtdblock_release,
342 .readsect = mtdblock_readsect,
343 .writesect = mtdblock_writesect,
344 .add_mtd = mtdblock_add_mtd,
345 .remove_dev = mtdblock_remove_dev,
346 .owner = THIS_MODULE,
349 static int __init init_mtdblock(void)
351 return register_mtd_blktrans(&mtdblock_tr);
354 static void __exit cleanup_mtdblock(void)
356 deregister_mtd_blktrans(&mtdblock_tr);
359 module_init(init_mtdblock);
360 module_exit(cleanup_mtdblock);
363 MODULE_LICENSE("GPL");
364 MODULE_AUTHOR("Nicolas Pitre <nico@fluxnic.net> et al.");
365 MODULE_DESCRIPTION("Caching read/erase/writeback block device emulation access to MTD devices");