[PATCH v2 1/4] mtdchar: calculate OOB capacity from the starting column

[James Hilliard <james.hilliard1@gmail.com>]

adjust_oob_length() needs the number of pages covered by an operation,
not their absolute indices. Calculate that count from the initial page
column and the data length instead of subtracting absolute page numbers.

Use a u64 product for the resulting OOB capacity before limiting the
requested OOB length. This keeps the calculation independent of the
absolute flash offset and avoids narrowing the capacity before the
comparison.

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
 drivers/mtd/mtdchar.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index bf01e6ac7293..19d33dacb62d 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -576,18 +576,17 @@ static int mtdchar_blkpg_ioctl(struct mtd_info *mtd,
 static void adjust_oob_length(struct mtd_info *mtd, uint64_t start,
 			      struct mtd_oob_ops *ops)
 {
-	uint32_t start_page, end_page;
+	u64 pages;
 	u32 oob_per_page;
 
 	if (ops->len == 0 || ops->ooblen == 0)
 		return;
 
-	start_page = mtd_div_by_ws(start, mtd);
-	end_page = mtd_div_by_ws(start + ops->len - 1, mtd);
+	pages = mtd_div_by_ws(mtd_mod_by_ws(start, mtd) + (u64)ops->len - 1,
+			      mtd) + 1;
 	oob_per_page = mtd_oobavail(mtd, ops);
 
-	ops->ooblen = min_t(size_t, ops->ooblen,
-			    (end_page - start_page + 1) * oob_per_page);
+	ops->ooblen = min_t(u64, ops->ooblen, pages * oob_per_page);
 }
 
 static noinline_for_stack int

-- 
2.53.0