drivers/mtd/mtdblock.c

   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");