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         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");