mtd: core: Fix erase area alignment for non power of 2 erasesize

On Thu, Jan 10, 2019 at 09:32:07AM +0100, Sascha Hauer wrote:
> On Wed, Jan 09, 2019 at 12:28:14PM +0100, Ladislav Michl wrote:
> > Devices as AT45DB161 DataFlash uses non power of two page size (528)
> > while present alignment algorithm relies on erasesize being power
> > of 2.
> > Fix that by introducing helper functions rounding to any multiply.
> > Note that logic is sligthly changed to be consistent as ending
> > address is moved forward to include also last byte meant to be
> > erased while previous implementation moved it backward.
> >
> > Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
> > ---
> >  drivers/mtd/core.c     | 28 ++++++++++++++++++++++------
> >  include/linux/kernel.h |  5 +++++
> >  2 files changed, 27 insertions(+), 6 deletions(-)
>
> Applied, thanks

Hi Sascha,

I was searching for paper bag, but was unable to find anything thick
enouh to cover behind :-/ This version is buggy and I noticed right
now when testing on another board. Corrected version follows, which
is also 192 bytes shorter for my ARM target. It seems next branch
at https://git.pengutronix.de/ is not yet updated, so perhaps my fault
won't affect anyone.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 19 insertions, 6 deletions

diff --git a/drivers/mtd/core.c b/drivers/mtd/core.c
index d3cbe502fa..f44c6cfc69 100644
--- a/drivers/mtd/core.c
+++ b/drivers/mtd/core.c
@@ -141,15 +141,28 @@ static struct mtd_erase_region_info *mtd_find_erase_region(struct mtd_info *mtd,
 	return NULL;
 }
 
+static loff_t __mtd_erase_round(loff_t x, uint32_t esize, int up)
+{
+	uint64_t dividend = x;
+	uint32_t mod = do_div(dividend, esize);
+	if (mod == 0)
+		return x;
+	if (up)
+		x += esize;
+	return x - mod;
+}
+#define mtd_erase_round_up(x, esize)	__mtd_erase_round(x, esize, 1)
+#define mtd_erase_round_down(x, esize)	__mtd_erase_round(x, esize, 0)
+
 static int mtd_erase_align(struct mtd_info *mtd, loff_t *count, loff_t *offset)
 {
 	struct mtd_erase_region_info *e;
 	loff_t ofs;
 
 	if (mtd->numeraseregions == 0) {
-		ofs = *offset & ~(loff_t)(mtd->erasesize - 1);
-		*count += (*offset - ofs);
-		*count = ALIGN(*count, mtd->erasesize);
+		ofs = mtd_erase_round_down(*offset, mtd->erasesize);
+		*count += *offset - ofs;
+		*count = mtd_erase_round_up(*count, mtd->erasesize);
 		*offset = ofs;
 		return 0;
 	}
@@ -158,14 +171,14 @@ static int mtd_erase_align(struct mtd_info *mtd, loff_t *count, loff_t *offset)
 	if (!e)
 		return -EINVAL;
 
-	ofs = *offset & ~(e->erasesize - 1);
-	*count += (*offset - ofs);
+	ofs = mtd_erase_round_down(*offset, e->erasesize);
+	*count += *offset - ofs;
 
 	e = mtd_find_erase_region(mtd, *offset + *count);
 	if (!e)
 		return -EINVAL;
 
-	*count = ALIGN(*count, e->erasesize);
+	*count = mtd_erase_round_up(*count, e->erasesize);
 	*offset = ofs;
 
 	return 0;