mtd: improve calculating partition boundaries when checking for alignment

When checking for alignment mtd should check absolute offsets. It's
important for subpartitions as it doesn't make sense to check their
relative addresses.
Signed-off-by: NRafał Miłecki <rafal@milecki.pl>
Signed-off-by: NBoris Brezillon <boris.brezillon@bootlin.com>

drivers/mtd/mtdpart.c

@@ -61,6 +61,15 @@ static inline struct mtd_part *mtd_to_part(const struct mtd_info *mtd)
 	return container_of(mtd, struct mtd_part, mtd);
 }
 
+static u64 part_absolute_offset(struct mtd_info *mtd)
+{
+	struct mtd_part *part = mtd_to_part(mtd);
+
+	if (!mtd_is_partition(mtd))
+		return 0;
+
+	return part_absolute_offset(part->parent) + part->offset;
+}
 
 /*
  * MTD methods which simply translate the effective address and pass through
@@ -514,7 +523,7 @@ static struct mtd_part *allocate_partition(struct mtd_info *parent,
 	if (!(slave->mtd.flags & MTD_NO_ERASE))
 		wr_alignment = slave->mtd.erasesize;
 
-	tmp = slave->offset;
+	tmp = part_absolute_offset(parent) + slave->offset;
 	remainder = do_div(tmp, wr_alignment);
 	if ((slave->mtd.flags & MTD_WRITEABLE) && remainder) {
 		/* Doesn't start on a boundary of major erase size */
@@ -525,7 +534,7 @@ static struct mtd_part *allocate_partition(struct mtd_info *parent,
 			part->name);
 	}
 
-	tmp = slave->mtd.size;
+	tmp = part_absolute_offset(parent) + slave->mtd.size;
 	remainder = do_div(tmp, wr_alignment);
 	if ((slave->mtd.flags & MTD_WRITEABLE) && remainder) {
 		slave->mtd.flags &= ~MTD_WRITEABLE;