openwrtv4/target/linux/generic/patches-4.9/412-mtd-partial_eraseblock_unlock.patch

--- a/drivers/mtd/mtdpart.c
+++ b/drivers/mtd/mtdpart.c
@@ -343,7 +343,16 @@ static int part_lock(struct mtd_info *mt
 static int part_unlock(struct mtd_info *mtd, loff_t ofs, uint64_t len)
 {
 	struct mtd_part *part = mtd_to_part(mtd);
-	return part->parent->_unlock(part->parent, 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->parent) + 1) * part->parent->erasesize;
+		ofs &= ~(part->parent->erasesize - 1);
+	}
+
+	return part->parent->_unlock(part->parent, ofs, len);
 }
 
 static int part_is_locked(struct mtd_info *mtd, loff_t ofs, uint64_t len)