mtd: allow partial block unlock

This allows sysupgrade for devices such as the Gateworks Avila/Cambria
product families based on the ixp4xx using the redboot bootloader with
combined FIS directory and RedBoot config partitions on larger FLASH
devices with larger eraseblocks.

This second iteration of this patch addresses previous issues:
  - whitespace breakage fixed
  - unlock in all scenarios
  - simplification and fix logic bug

Signed-off-by: Tim Harvey <tharvey@gateworks.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@33681 3c298f89-4303-0410-b956-a3cf2f4a3e73

target/linux/generic/patches-3.3/478-mtd-partial_eraseblock_unlock.patch

@@ -0,0 +1,18 @@
+--- a/drivers/mtd/mtdpart.c
++++ b/drivers/mtd/mtdpart.c
+@@ -356,7 +356,14 @@ static int part_unlock(struct mtd_info *
+ 	struct mtd_part *part = PART(mtd);
+ 	if ((len + ofs) > mtd->size)
+ 		return -EINVAL;
+-	return mtd_unlock(part->master, ofs + part->offset, len);
++
++	ofs += part->offset;
++	if (mtd->flags & MTD_ERASE_PARTIAL) {
++		/* round up len to next erasesize and round down offset to prev block */
++		len = (mtd_div_by_eb(len, part->master) + 1) * part->master->erasesize;
++		ofs &= ~(part->master->erasesize - 1);
++	}
++	return mtd_unlock(part->master, ofs, len);
+ }
+ 
+ static int part_is_locked(struct mtd_info *mtd, loff_t ofs, uint64_t len)