UBI: use mtd->writebufsize to set minimal I/O unit size

[deliverable/linux.git] / drivers / mtd / ubi / build.c

diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index 5ebe280225d60a69f28bc81c5c4593a47e017365..f49e49dc5928cf1acfa5b25d019162f99a3eb1db 100644 (file)
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -672,7 +672,33 @@ static int io_init(struct ubi_device *ubi)
                ubi->nor_flash = 1;
        }
 
-       ubi->min_io_size = ubi->mtd->writesize;
+       /*
+        * Set UBI min. I/O size (@ubi->min_io_size). We use @mtd->writebufsize
+        * for these purposes, not @mtd->writesize. At the moment this does not
+        * matter for NAND, because currently @mtd->writebufsize is equivalent to
+        * @mtd->writesize for all NANDs. However, some CFI NOR flashes may
+        * have @mtd->writebufsize which is multiple of @mtd->writesize.
+        *
+        * The reason we use @mtd->writebufsize for @ubi->min_io_size is that
+        * UBI and UBIFS recovery algorithms rely on the fact that if there was
+        * an unclean power cut, then we can find offset of the last corrupted
+        * node, align the offset to @ubi->min_io_size, read the rest of the
+        * eraseblock starting from this offset, and check whether there are
+        * only 0xFF bytes. If yes, then we are probably dealing with a
+        * corruption caused by a power cut, if not, then this is probably some
+        * severe corruption.
+        *
+        * Thus, we have to use the maximum write unit size of the flash, which
+        * is @mtd->writebufsize, because @mtd->writesize is the minimum write
+        * size, not the maximum.
+        */
+       if (ubi->mtd->type == MTD_NANDFLASH)
+               ubi_assert(ubi->mtd->writebufsize == ubi->mtd->writesize);
+       else if (ubi->mtd->type == MTD_NORFLASH)
+               ubi_assert(ubi->mtd->writebufsize % ubi->mtd->writesize == 0);
+
+       ubi->min_io_size = ubi->mtd->writebufsize;
+
        ubi->hdrs_min_io_size = ubi->mtd->writesize >> ubi->mtd->subpage_sft;
 
        /*