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 if (ret)
93 return ret;
94
95 /*
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.
101 */
102 mtdblk->cache_state = STATE_EMPTY;
103 return 0;
104 }
105
106
do_cached_write(struct mtdblk_dev * mtdblk,unsigned long pos,int len,const char * buf)107 static int do_cached_write (struct mtdblk_dev *mtdblk, unsigned long pos,
108 int len, const char *buf)
109 {
110 struct mtd_info *mtd = mtdblk->mbd.mtd;
111 unsigned int sect_size = mtdblk->cache_size;
112 size_t retlen;
113 int ret;
114
115 pr_debug("mtdblock: write on \"%s\" at 0x%lx, size 0x%x\n",
116 mtd->name, pos, len);
117
118 if (!sect_size)
119 return mtd_write(mtd, pos, len, &retlen, buf);
120
121 while (len > 0) {
122 unsigned long sect_start = (pos/sect_size)*sect_size;
123 unsigned int offset = pos - sect_start;
124 unsigned int size = sect_size - offset;
125 if( size > len )
126 size = len;
127
128 if (size == sect_size) {
129 /*
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.
133 */
134 ret = erase_write (mtd, pos, size, buf);
135 if (ret)
136 return ret;
137 } else {
138 /* Partial sector: need to use the cache */
139
140 if (mtdblk->cache_state == STATE_DIRTY &&
141 mtdblk->cache_offset != sect_start) {
142 ret = write_cached_data(mtdblk);
143 if (ret)
144 return ret;
145 }
146
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))
154 return ret;
155 if (retlen != sect_size)
156 return -EIO;
157
158 mtdblk->cache_offset = sect_start;
159 mtdblk->cache_size = sect_size;
160 mtdblk->cache_state = STATE_CLEAN;
161 }
162
163 /* write data to our local cache */
164 memcpy (mtdblk->cache_data + offset, buf, size);
165 mtdblk->cache_state = STATE_DIRTY;
166 }
167
168 buf += size;
169 pos += size;
170 len -= size;
171 }
172
173 return 0;
174 }
175
176
do_cached_read(struct mtdblk_dev * mtdblk,unsigned long pos,int len,char * buf)177 static int do_cached_read (struct mtdblk_dev *mtdblk, unsigned long pos,
178 int len, char *buf)
179 {
180 struct mtd_info *mtd = mtdblk->mbd.mtd;
181 unsigned int sect_size = mtdblk->cache_size;
182 size_t retlen;
183 int ret;
184
185 pr_debug("mtdblock: read on \"%s\" at 0x%lx, size 0x%x\n",
186 mtd->name, pos, len);
187
188 if (!sect_size) {
189 ret = mtd_read(mtd, pos, len, &retlen, buf);
190 if (ret && !mtd_is_bitflip(ret))
191 return ret;
192 return 0;
193 }
194
195 while (len > 0) {
196 unsigned long sect_start = (pos/sect_size)*sect_size;
197 unsigned int offset = pos - sect_start;
198 unsigned int size = sect_size - offset;
199 if (size > len)
200 size = len;
201
202 /*
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
206 * from flash.
207 */
208 if (mtdblk->cache_state != STATE_EMPTY &&
209 mtdblk->cache_offset == sect_start) {
210 memcpy (buf, mtdblk->cache_data + offset, size);
211 } else {
212 ret = mtd_read(mtd, pos, size, &retlen, buf);
213 if (ret && !mtd_is_bitflip(ret))
214 return ret;
215 if (retlen != size)
216 return -EIO;
217 }
218
219 buf += size;
220 pos += size;
221 len -= size;
222 }
223
224 return 0;
225 }
226
mtdblock_readsect(struct mtd_blktrans_dev * dev,unsigned long block,char * buf)227 static int mtdblock_readsect(struct mtd_blktrans_dev *dev,
228 unsigned long block, char *buf)
229 {
230 struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);
231 return do_cached_read(mtdblk, block<<9, 512, buf);
232 }
233
mtdblock_writesect(struct mtd_blktrans_dev * dev,unsigned long block,char * buf)234 static int mtdblock_writesect(struct mtd_blktrans_dev *dev,
235 unsigned long block, char *buf)
236 {
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)
241 return -EINTR;
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?
245 */
246 }
247 return do_cached_write(mtdblk, block<<9, 512, buf);
248 }
249
mtdblock_open(struct mtd_blktrans_dev * mbd)250 static int mtdblock_open(struct mtd_blktrans_dev *mbd)
251 {
252 struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd);
253
254 pr_debug("mtdblock_open\n");
255
256 if (mtdblk->count) {
257 mtdblk->count++;
258 return 0;
259 }
260
261 /* OK, it's not open. Create cache info for it */
262 mtdblk->count = 1;
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;
268 }
269
270 pr_debug("ok\n");
271
272 return 0;
273 }
274
mtdblock_release(struct mtd_blktrans_dev * mbd)275 static void mtdblock_release(struct mtd_blktrans_dev *mbd)
276 {
277 struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd);
278
279 pr_debug("mtdblock_release\n");
280
281 mutex_lock(&mtdblk->cache_mutex);
282 write_cached_data(mtdblk);
283 mutex_unlock(&mtdblk->cache_mutex);
284
285 if (!--mtdblk->count) {
286 /*
287 * It was the last usage. Free the cache, but only sync if
288 * opened for writing.
289 */
290 if (mbd->file_mode & FMODE_WRITE)
291 mtd_sync(mbd->mtd);
292 vfree(mtdblk->cache_data);
293 }
294
295 pr_debug("ok\n");
296 }
297
mtdblock_flush(struct mtd_blktrans_dev * dev)298 static int mtdblock_flush(struct mtd_blktrans_dev *dev)
299 {
300 struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd);
301
302 mutex_lock(&mtdblk->cache_mutex);
303 write_cached_data(mtdblk);
304 mutex_unlock(&mtdblk->cache_mutex);
305 mtd_sync(dev->mtd);
306 return 0;
307 }
308
mtdblock_add_mtd(struct mtd_blktrans_ops * tr,struct mtd_info * mtd)309 static void mtdblock_add_mtd(struct mtd_blktrans_ops *tr, struct mtd_info *mtd)
310 {
311 struct mtdblk_dev *dev = kzalloc(sizeof(*dev), GFP_KERNEL);
312
313 if (!dev)
314 return;
315
316 dev->mbd.mtd = mtd;
317 dev->mbd.devnum = mtd->index;
318
319 dev->mbd.size = mtd->size >> 9;
320 dev->mbd.tr = tr;
321
322 if (!(mtd->flags & MTD_WRITEABLE))
323 dev->mbd.readonly = 1;
324
325 if (add_mtd_blktrans_dev(&dev->mbd))
326 kfree(dev);
327 }
328
mtdblock_remove_dev(struct mtd_blktrans_dev * dev)329 static void mtdblock_remove_dev(struct mtd_blktrans_dev *dev)
330 {
331 del_mtd_blktrans_dev(dev);
332 }
333
334 static struct mtd_blktrans_ops mtdblock_tr = {
335 .name = "mtdblock",
336 .major = MTD_BLOCK_MAJOR,
337 .part_bits = 0,
338 .blksize = 512,
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,
347 };
348
init_mtdblock(void)349 static int __init init_mtdblock(void)
350 {
351 return register_mtd_blktrans(&mtdblock_tr);
352 }
353
cleanup_mtdblock(void)354 static void __exit cleanup_mtdblock(void)
355 {
356 deregister_mtd_blktrans(&mtdblock_tr);
357 }
358
359 module_init(init_mtdblock);
360 module_exit(cleanup_mtdblock);
361
362
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");
366