3 files changed, 64 insertions, 3 deletions

diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index db0b9cb64c6c..e1f7d0a78b9d 100644
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -657,6 +657,11 @@ static int io_init(struct ubi_device *ubi)
         if (ubi->mtd->block_isbad && ubi->mtd->block_markbad)
                 ubi->bad_allowed = 1;
 
+        if (ubi->mtd->type == MTD_NORFLASH) {
+                ubi_assert(ubi->mtd->writesize == 1);
+                ubi->nor_flash = 1;
+        }
+
         ubi->min_io_size = ubi->mtd->writesize;
         ubi->hdrs_min_io_size = ubi->mtd->writesize >> ubi->mtd->subpage_sft;
 
diff --git a/drivers/mtd/ubi/io.c b/drivers/mtd/ubi/io.c
index 1ea14218de02..c3bd2e34c642 100644
--- a/drivers/mtd/ubi/io.c
+++ b/drivers/mtd/ubi/io.c
@@ -266,8 +266,8 @@ int ubi_io_write(struct ubi_device *ubi, const void *buf, int pnum, int offset,
         addr = (loff_t)pnum * ubi->peb_size + offset;
         err = ubi->mtd->write(ubi->mtd, addr, len, &written, buf);
         if (err) {
-                ubi_err("error %d while writing %d bytes to PEB %d:%d, written"
-                        " %zd bytes", err, len, pnum, offset, written);
+                ubi_err("error %d while writing %d bytes to PEB %d:%d, written "
+                        "%zd bytes", err, len, pnum, offset, written);
                 ubi_dbg_dump_stack();
         } else
                 ubi_assert(written == len);
@@ -454,6 +454,54 @@ out:
 }
 
 /**
+ * nor_erase_prepare - prepare a NOR flash PEB for erasure.
+ * @ubi: UBI device description object
+ * @pnum: physical eraseblock number to prepare
+ *
+ * NOR flash, or at least some of them, have peculiar embedded PEB erasure
+ * algorithm: the PEB is first filled with zeroes, then it is erased. And
+ * filling with zeroes starts from the end of the PEB. This was observed with
+ * Spansion S29GL512N NOR flash.
+ *
+ * This means that in case of a power cut we may end up with intact data at the
+ * beginning of the PEB, and all zeroes at the end of PEB. In other words, the
+ * EC and VID headers are OK, but a large chunk of data at the end of PEB is
+ * zeroed. This makes UBI mistakenly treat this PEB as used and associate it
+ * with an LEB, which leads to subsequent failures (e.g., UBIFS fails).
+ *
+ * This function is called before erasing NOR PEBs and it zeroes out EC and VID
+ * magic numbers in order to invalidate them and prevent the failures. Returns
+ * zero in case of success and a negative error code in case of failure.
+ */
+static int nor_erase_prepare(struct ubi_device *ubi, int pnum)
+{
+        int err;
+        size_t written;
+        loff_t addr;
+        uint32_t data = 0;
+
+        addr = (loff_t)pnum * ubi->peb_size;
+        err = ubi->mtd->write(ubi->mtd, addr, 4, &written, &data);
+        if (err) {
+                ubi_err("error %d while writing 4 bytes to PEB %d:0, written "
+                        "%zd bytes", err, pnum, 0, written);
+                ubi_dbg_dump_stack();
+                return err;
+        }
+
+        addr += ubi->vid_hdr_aloffset;
+        err = ubi->mtd->write(ubi->mtd, addr, 4, &written, &data);
+        if (err) {
+                ubi_err("error %d while writing 4 bytes to PEB %d:%d, written "
+                        "%zd bytes", err, pnum, ubi->vid_hdr_aloffset, written);
+                ubi_dbg_dump_stack();
+                return err;
+        }
+
+        return 0;
+}
+
+/**
  * ubi_io_sync_erase - synchronously erase a physical eraseblock.
  * @ubi: UBI device description object
  * @pnum: physical eraseblock number to erase
@@ -484,6 +532,12 @@ int ubi_io_sync_erase(struct ubi_device *ubi, int pnum, int torture)
                 return -EROFS;
         }
 
+        if (ubi->nor_flash) {
+                err = nor_erase_prepare(ubi, pnum);
+                if (err)
+                        return err;
+        }
+
         if (torture) {
                 ret = torture_peb(ubi, pnum);
                 if (ret < 0)
diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
index 64604e8809ec..6a5fe9633783 100644
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -373,6 +373,7 @@ struct ubi_wl_entry;
  * @vid_hdr_shift: contains @vid_hdr_offset - @vid_hdr_aloffset
  * @bad_allowed: whether the MTD device admits of bad physical eraseblocks or
  *               not
+ * @nor_flash: non-zero if working on top of NOR flash
  * @mtd: MTD device descriptor
  *
  * @peb_buf1: a buffer of PEB size used for different purposes
@@ -454,7 +455,8 @@ struct ubi_device {
         int vid_hdr_offset;
         int vid_hdr_aloffset;
         int vid_hdr_shift;
-        int bad_allowed;
+        unsigned int bad_allowed:1;
+        unsigned int nor_flash:1;
         struct mtd_info *mtd;
 
         void *peb_buf1;