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 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 } 108 109 110 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) 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 } 178 179 180 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 return mtd_read(mtd, pos, len, &retlen, buf); 193 194 while (len > 0) { 195 unsigned long sect_start = (pos/sect_size)*sect_size; 196 unsigned int offset = pos - sect_start; 197 unsigned int size = sect_size - offset; 198 if (size > len) 199 size = len; 200 201 /* 202 * Check if the requested data is already cached 203 * Read the requested amount of data from our internal cache if it 204 * contains what we want, otherwise we read the data directly 205 * from flash. 206 */ 207 if (mtdblk->cache_state != STATE_EMPTY && 208 mtdblk->cache_offset == sect_start) { 209 memcpy (buf, mtdblk->cache_data + offset, size); 210 } else { 211 ret = mtd_read(mtd, pos, size, &retlen, buf); 212 if (ret) 213 return ret; 214 if (retlen != size) 215 return -EIO; 216 } 217 218 buf += size; 219 pos += size; 220 len -= size; 221 } 222 223 return 0; 224 } 225 226 static int mtdblock_readsect(struct mtd_blktrans_dev *dev, 227 unsigned long block, char *buf) 228 { 229 struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd); 230 return do_cached_read(mtdblk, block<<9, 512, buf); 231 } 232 233 static int mtdblock_writesect(struct mtd_blktrans_dev *dev, 234 unsigned long block, char *buf) 235 { 236 struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd); 237 if (unlikely(!mtdblk->cache_data && mtdblk->cache_size)) { 238 mtdblk->cache_data = vmalloc(mtdblk->mbd.mtd->erasesize); 239 if (!mtdblk->cache_data) 240 return -EINTR; 241 /* -EINTR is not really correct, but it is the best match 242 * documented in man 2 write for all cases. We could also 243 * return -EAGAIN sometimes, but why bother? 244 */ 245 } 246 return do_cached_write(mtdblk, block<<9, 512, buf); 247 } 248 249 static int mtdblock_open(struct mtd_blktrans_dev *mbd) 250 { 251 struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd); 252 253 pr_debug("mtdblock_open\n"); 254 255 if (mtdblk->count) { 256 mtdblk->count++; 257 return 0; 258 } 259 260 /* OK, it's not open. Create cache info for it */ 261 mtdblk->count = 1; 262 mutex_init(&mtdblk->cache_mutex); 263 mtdblk->cache_state = STATE_EMPTY; 264 if (!(mbd->mtd->flags & MTD_NO_ERASE) && mbd->mtd->erasesize) { 265 mtdblk->cache_size = mbd->mtd->erasesize; 266 mtdblk->cache_data = NULL; 267 } 268 269 pr_debug("ok\n"); 270 271 return 0; 272 } 273 274 static void mtdblock_release(struct mtd_blktrans_dev *mbd) 275 { 276 struct mtdblk_dev *mtdblk = container_of(mbd, struct mtdblk_dev, mbd); 277 278 pr_debug("mtdblock_release\n"); 279 280 mutex_lock(&mtdblk->cache_mutex); 281 write_cached_data(mtdblk); 282 mutex_unlock(&mtdblk->cache_mutex); 283 284 if (!--mtdblk->count) { 285 /* 286 * It was the last usage. Free the cache, but only sync if 287 * opened for writing. 288 */ 289 if (mbd->file_mode & FMODE_WRITE) 290 mtd_sync(mbd->mtd); 291 vfree(mtdblk->cache_data); 292 } 293 294 pr_debug("ok\n"); 295 } 296 297 static int mtdblock_flush(struct mtd_blktrans_dev *dev) 298 { 299 struct mtdblk_dev *mtdblk = container_of(dev, struct mtdblk_dev, mbd); 300 int ret; 301 302 mutex_lock(&mtdblk->cache_mutex); 303 ret = write_cached_data(mtdblk); 304 mutex_unlock(&mtdblk->cache_mutex); 305 mtd_sync(dev->mtd); 306 return ret; 307 } 308 309 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 } 328 329 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 }; 348 349 static int __init init_mtdblock(void) 350 { 351 return register_mtd_blktrans(&mtdblock_tr); 352 } 353 354 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