1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * Direct MTD block device access
4 *
5 * Copyright © 1999-2010 David Woodhouse <dwmw2@infradead.org>
6 * Copyright © 2000-2003 Nicolas Pitre <nico@fluxnic.net>
7 */
8
9 #include <linux/fs.h>
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>
17
18 #include <linux/mtd/mtd.h>
19 #include <linux/mtd/blktrans.h>
20 #include <linux/mutex.h>
21 #include <linux/major.h>
22
23
24 struct mtdblk_dev {
25 struct mtd_blktrans_dev mbd;
26 int count;
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;
32 };
33
34 /*
35 * Cache stuff...
36 *
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.
42 */
43
erase_write(struct mtd_info * mtd,unsigned long pos,unsigned int len,const char * buf)44 static int erase_write (struct mtd_info *mtd, unsigned long pos,
45 unsigned int len, const char *buf)
46 {
47 struct erase_info erase;
48 size_t retlen;
49 int ret;
50
51 /*
52 * First, let's erase the flash block.
53 */
54 erase.addr = pos;
55 erase.len = len;
56
57 ret = mtd_erase(mtd, &erase);
58 if (ret) {
59 printk (KERN_WARNING "mtdblock: erase of region [0x%lx, 0x%x] "
60 "on \"%s\" failed\n",
61 pos, len, mtd->name);
62 return ret;
63 }
64
65 /*
66 * Next, write the data to flash.
67 */
68
69 ret = mtd_write(mtd, pos, len, &retlen, buf);
70 if (ret)
71 return ret;
72 if (retlen != len)
73 return -EIO;
74 return 0;
75 }
76
77
write_cached_data(struct mtdblk_dev * mtdblk)78 static int write_cached_data (struct mtdblk_dev *mtdblk)
79 {
80 struct mtd_info *mtd = mtdblk->mbd.mtd;
81 int ret;
82
83 if (mtdblk->cache_state != STATE_DIRTY)
84 return 0;
85
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);
89
90 ret = erase_write (mtd, mtdblk->cache_offset,
91 mtdblk->cache_size, mtdblk->cache_data);
92
93 /*
94 * Here we could arguably set the cache state to STATE_CLEAN.
95 * However this could lead to inconsistency since we will not
96 * be notified if this content is altered on the flash by other
97 * means. Let's declare it empty and leave buffering tasks to
98 * the buffer cache instead.
99 *
100 * If this cache_offset points to a bad block, data cannot be
101 * written to the device. Clear cache_state to avoid writing to
102 * bad blocks repeatedly.
103 */
104 if (ret == 0 || ret == -EIO)
105 mtdblk->cache_state = STATE_EMPTY;
106 return ret;
107 }
108
109
do_cached_write(struct mtdblk_dev * mtdblk,unsigned long pos,int len,const char * buf)110 static int do_cached_write (struct mtdblk_dev *mtdblk, unsigned long pos,
111 int len, const char *buf)
112 {
113 struct mtd_info *mtd = mtdblk->mbd.mtd;
114 unsigned int sect_size = mtdblk->cache_size;
115 size_t retlen;
116 int ret;
117
118 pr_debug("mtdblock: write on \"%s\" at 0x%lx, size 0x%x\n",
119 mtd->name, pos, len);
120
121 if (!sect_size)
122 return mtd_write(mtd, pos, len, &retlen, buf);
123
124 while (len > 0) {
125 unsigned long sect_start = (pos/sect_size)*sect_size;
126 unsigned int offset = pos - sect_start;
127 unsigned int size = sect_size - offset;
128 if( size > len )
129 size = len;
130
131 if (size == sect_size) {
132 /*
133 * We are covering a whole sector. Thus there is no
134 * need to bother with the cache while it may still be
135 * useful for other partial writes.
136 */
137 ret = erase_write (mtd, pos, size, buf);
138 if (ret)
139 return ret;
140 } else {
141 /* Partial sector: need to use the cache */
142
143 if (mtdblk->cache_state == STATE_DIRTY &&
144 mtdblk->cache_offset != sect_start) {
145 ret = write_cached_data(mtdblk);
146 if (ret)
147 return ret;
148 }
149
150 if (mtdblk->cache_state == STATE_EMPTY ||
151 mtdblk->cache_offset != sect_start) {
152 /* fill the cache with the current sector */
153 mtdblk->cache_state = STATE_EMPTY;
154 ret = mtd_read(mtd, sect_start, sect_size,
155 &retlen, mtdblk->cache_data);
156 if (ret && !mtd_is_bitflip(ret))
157 return ret;
158 if (retlen != sect_size)
159 return -EIO;
160
161 mtdblk->cache_offset = sect_start;
162 mtdblk->cache_size = sect_size;
163 mtdblk->cache_state = STATE_CLEAN;
164 }
165
166 /* write data to our local cache */
167 memcpy (mtdblk->cache_data + offset, buf, size);
168 mtdblk->cache_state = STATE_DIRTY;
169 }
170
171 buf += size;
172 pos += size;
173 len -= size;
174 }
175
176 return 0;
177 }
178
179
do_cached_read(struct mtdblk_dev * mtdblk,unsigned long pos,int len,char * buf)180 static int do_cached_read (struct mtdblk_dev *mtdblk, unsigned long pos,
181 int len, char *buf)
182 {
183 struct mtd_info *mtd = mtdblk->mbd.mtd;
184 unsigned int sect_size = mtdblk->cache_size;
185 size_t retlen;
186 int ret;
187
188 pr_debug("mtdblock: read on \"%s\" at 0x%lx, size 0x%x\n",
189 mtd->name, pos, len);
190
191 if (!sect_size) {
192 ret = mtd_read(mtd, pos, len, &retlen, buf);
193 if (ret && !mtd_is_bitflip(ret))
194 return ret;
195 return 0;
196 }
197
198 while (len > 0) {
199 unsigned long sect_start = (pos/sect_size)*sect_size;
200 unsigned int offset = pos - sect_start;
201 unsigned int size = sect_size - offset;
202 if (size > len)
203 size = len;
204
205 /*
206 * Check if the requested data is already cached
207 * Read the requested amount of data from our internal cache if it
208 * contains what we want, otherwise we read the data directly
209 * from flash.
210 */
211 if (mtdblk->cache_state != STATE_EMPTY &&
212 mtdblk->cache_offset == sect_start) {
213 memcpy (buf, mtdblk->cache_data + offset, size);
214 } else {
215 ret = mtd_read(mtd, pos, size, &retlen, buf);
216 if (ret && !mtd_is_bitflip(ret))
217 return ret;
218 if (retlen != size)
219 return -EIO;
220 }
221
222 buf += size;
223 pos += size;
224 len -= size;
225 }
226
227 return 0;
228 }
229
mtdblock_readsect(struct mtd_blktrans_dev * dev,unsigned long block,char * buf)230 static int mtdblock_readsect(struct mtd_blktrans_dev *dev,
231 unsigned long block, char *buf)
232 {
233 struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);
234 return do_cached_read(mtdblk, block<<9, 512, buf);
235 }
236
mtdblock_writesect(struct mtd_blktrans_dev * dev,unsigned long block,char * buf)237 static int mtdblock_writesect(struct mtd_blktrans_dev *dev,
238 unsigned long block, char *buf)
239 {
240 struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);
241 if (unlikely(!mtdblk->cache_data && mtdblk->cache_size)) {
242 mtdblk->cache_data = vmalloc(mtdblk->mbd.mtd->erasesize);
243 if (!mtdblk->cache_data)
244 return -EINTR;
245 /* -EINTR is not really correct, but it is the best match
246 * documented in man 2 write for all cases. We could also
247 * return -EAGAIN sometimes, but why bother?
248 */
249 }
250 return do_cached_write(mtdblk, block<<9, 512, buf);
251 }
252
mtdblock_open(struct mtd_blktrans_dev * mbd)253 static int mtdblock_open(struct mtd_blktrans_dev *mbd)
254 {
255 struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd);
256
257 pr_debug("mtdblock_open\n");
258
259 if (mtdblk->count) {
260 mtdblk->count++;
261 return 0;
262 }
263
264 /* OK, it's not open. Create cache info for it */
265 mtdblk->count = 1;
266 mutex_init(&mtdblk->cache_mutex);
267 mtdblk->cache_state = STATE_EMPTY;
268 if (!(mbd->mtd->flags & MTD_NO_ERASE) && mbd->mtd->erasesize) {
269 mtdblk->cache_size = mbd->mtd->erasesize;
270 mtdblk->cache_data = NULL;
271 }
272
273 pr_debug("ok\n");
274
275 return 0;
276 }
277
mtdblock_release(struct mtd_blktrans_dev * mbd)278 static void mtdblock_release(struct mtd_blktrans_dev *mbd)
279 {
280 struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd);
281
282 pr_debug("mtdblock_release\n");
283
284 mutex_lock(&mtdblk->cache_mutex);
285 write_cached_data(mtdblk);
286 mutex_unlock(&mtdblk->cache_mutex);
287
288 if (!--mtdblk->count) {
289 /*
290 * It was the last usage. Free the cache, but only sync if
291 * opened for writing.
292 */
293 if (mbd->file_mode & FMODE_WRITE)
294 mtd_sync(mbd->mtd);
295 vfree(mtdblk->cache_data);
296 }
297
298 pr_debug("ok\n");
299 }
300
mtdblock_flush(struct mtd_blktrans_dev * dev)301 static int mtdblock_flush(struct mtd_blktrans_dev *dev)
302 {
303 struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);
304 int ret;
305
306 mutex_lock(&mtdblk->cache_mutex);
307 ret = write_cached_data(mtdblk);
308 mutex_unlock(&mtdblk->cache_mutex);
309 mtd_sync(dev->mtd);
310 return ret;
311 }
312
mtdblock_add_mtd(struct mtd_blktrans_ops * tr,struct mtd_info * mtd)313 static void mtdblock_add_mtd(struct mtd_blktrans_ops *tr, struct mtd_info *mtd)
314 {
315 struct mtdblk_dev *dev = kzalloc(sizeof(*dev), GFP_KERNEL);
316
317 if (!dev)
318 return;
319
320 dev->mbd.mtd = mtd;
321 dev->mbd.devnum = mtd->index;
322
323 dev->mbd.size = mtd->size >> 9;
324 dev->mbd.tr = tr;
325
326 if (!(mtd->flags & MTD_WRITEABLE))
327 dev->mbd.readonly = 1;
328
329 if (add_mtd_blktrans_dev(&dev->mbd))
330 kfree(dev);
331 }
332
mtdblock_remove_dev(struct mtd_blktrans_dev * dev)333 static void mtdblock_remove_dev(struct mtd_blktrans_dev *dev)
334 {
335 del_mtd_blktrans_dev(dev);
336 }
337
338 static struct mtd_blktrans_ops mtdblock_tr = {
339 .name = "mtdblock",
340 .major = MTD_BLOCK_MAJOR,
341 .part_bits = 0,
342 .blksize = 512,
343 .open = mtdblock_open,
344 .flush = mtdblock_flush,
345 .release = mtdblock_release,
346 .readsect = mtdblock_readsect,
347 .writesect = mtdblock_writesect,
348 .add_mtd = mtdblock_add_mtd,
349 .remove_dev = mtdblock_remove_dev,
350 .owner = THIS_MODULE,
351 };
352
init_mtdblock(void)353 static int __init init_mtdblock(void)
354 {
355 return register_mtd_blktrans(&mtdblock_tr);
356 }
357
cleanup_mtdblock(void)358 static void __exit cleanup_mtdblock(void)
359 {
360 deregister_mtd_blktrans(&mtdblock_tr);
361 }
362
363 module_init(init_mtdblock);
364 module_exit(cleanup_mtdblock);
365
366
367 MODULE_LICENSE("GPL");
368 MODULE_AUTHOR("Nicolas Pitre <nico@fluxnic.net> et al.");
369 MODULE_DESCRIPTION("Caching read/erase/writeback block device emulation access to MTD devices");
370