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 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 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 } 105 106 107 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) 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 } 175 176 177 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 return mtd_read(mtd, pos, len, &retlen, buf); 190 191 while (len > 0) { 192 unsigned long sect_start = (pos/sect_size)*sect_size; 193 unsigned int offset = pos - sect_start; 194 unsigned int size = sect_size - offset; 195 if (size > len) 196 size = len; 197 198 /* 199 * Check if the requested data is already cached 200 * Read the requested amount of data from our internal cache if it 201 * contains what we want, otherwise we read the data directly 202 * from flash. 203 */ 204 if (mtdblk->cache_state != STATE_EMPTY && 205 mtdblk->cache_offset == sect_start) { 206 memcpy (buf, mtdblk->cache_data + offset, size); 207 } else { 208 ret = mtd_read(mtd, pos, size, &retlen, buf); 209 if (ret) 210 return ret; 211 if (retlen != size) 212 return -EIO; 213 } 214 215 buf += size; 216 pos += size; 217 len -= size; 218 } 219 220 return 0; 221 } 222 223 static int mtdblock_readsect(struct mtd_blktrans_dev *dev, 224 unsigned long block, char *buf) 225 { 226 struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd); 227 return do_cached_read(mtdblk, block<<9, 512, buf); 228 } 229 230 static int mtdblock_writesect(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 if (unlikely(!mtdblk->cache_data && mtdblk->cache_size)) { 235 mtdblk->cache_data = vmalloc(mtdblk->mbd.mtd->erasesize); 236 if (!mtdblk->cache_data) 237 return -EINTR; 238 /* -EINTR is not really correct, but it is the best match 239 * documented in man 2 write for all cases. We could also 240 * return -EAGAIN sometimes, but why bother? 241 */ 242 } 243 return do_cached_write(mtdblk, block<<9, 512, buf); 244 } 245 246 static int mtdblock_open(struct mtd_blktrans_dev *mbd) 247 { 248 struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd); 249 250 pr_debug("mtdblock_open\n"); 251 252 if (mtdblk->count) { 253 mtdblk->count++; 254 return 0; 255 } 256 257 /* OK, it's not open. Create cache info for it */ 258 mtdblk->count = 1; 259 mutex_init(&mtdblk->cache_mutex); 260 mtdblk->cache_state = STATE_EMPTY; 261 if (!(mbd->mtd->flags & MTD_NO_ERASE) && mbd->mtd->erasesize) { 262 mtdblk->cache_size = mbd->mtd->erasesize; 263 mtdblk->cache_data = NULL; 264 } 265 266 pr_debug("ok\n"); 267 268 return 0; 269 } 270 271 static void mtdblock_release(struct mtd_blktrans_dev *mbd) 272 { 273 struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd); 274 275 pr_debug("mtdblock_release\n"); 276 277 mutex_lock(&mtdblk->cache_mutex); 278 write_cached_data(mtdblk); 279 mutex_unlock(&mtdblk->cache_mutex); 280 281 if (!--mtdblk->count) { 282 /* 283 * It was the last usage. Free the cache, but only sync if 284 * opened for writing. 285 */ 286 if (mbd->file_mode & FMODE_WRITE) 287 mtd_sync(mbd->mtd); 288 vfree(mtdblk->cache_data); 289 } 290 291 pr_debug("ok\n"); 292 } 293 294 static int mtdblock_flush(struct mtd_blktrans_dev *dev) 295 { 296 struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd); 297 298 mutex_lock(&mtdblk->cache_mutex); 299 write_cached_data(mtdblk); 300 mutex_unlock(&mtdblk->cache_mutex); 301 mtd_sync(dev->mtd); 302 return 0; 303 } 304 305 static void mtdblock_add_mtd(struct mtd_blktrans_ops *tr, struct mtd_info *mtd) 306 { 307 struct mtdblk_dev *dev = kzalloc(sizeof(*dev), GFP_KERNEL); 308 309 if (!dev) 310 return; 311 312 dev->mbd.mtd = mtd; 313 dev->mbd.devnum = mtd->index; 314 315 dev->mbd.size = mtd->size >> 9; 316 dev->mbd.tr = tr; 317 318 if (!(mtd->flags & MTD_WRITEABLE)) 319 dev->mbd.readonly = 1; 320 321 if (add_mtd_blktrans_dev(&dev->mbd)) 322 kfree(dev); 323 } 324 325 static void mtdblock_remove_dev(struct mtd_blktrans_dev *dev) 326 { 327 del_mtd_blktrans_dev(dev); 328 } 329 330 static struct mtd_blktrans_ops mtdblock_tr = { 331 .name = "mtdblock", 332 .major = MTD_BLOCK_MAJOR, 333 .part_bits = 0, 334 .blksize = 512, 335 .open = mtdblock_open, 336 .flush = mtdblock_flush, 337 .release = mtdblock_release, 338 .readsect = mtdblock_readsect, 339 .writesect = mtdblock_writesect, 340 .add_mtd = mtdblock_add_mtd, 341 .remove_dev = mtdblock_remove_dev, 342 .owner = THIS_MODULE, 343 }; 344 345 static int __init init_mtdblock(void) 346 { 347 return register_mtd_blktrans(&mtdblock_tr); 348 } 349 350 static void __exit cleanup_mtdblock(void) 351 { 352 deregister_mtd_blktrans(&mtdblock_tr); 353 } 354 355 module_init(init_mtdblock); 356 module_exit(cleanup_mtdblock); 357 358 359 MODULE_LICENSE("GPL"); 360 MODULE_AUTHOR("Nicolas Pitre <nico@fluxnic.net> et al."); 361 MODULE_DESCRIPTION("Caching read/erase/writeback block device emulation access to MTD devices"); 362