[PATCH] mmc: core: Fix off-by-one error in mmc_do_calc_max_discard()

David Jander
2015-06-01T09:49:30Z

qty is the maximum number of discard that _do_ fit in the timeout, not
the first amount that does _not_ fit anymore.
This seemingly harmless error has a very severe performance impact when
the timeout value is enough for only 1 erase group.

Signed-off-by: David Jander <david@protonic.nl>
---
drivers/mmc/core/core.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 92e7671..1f9573b 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -2234,16 +2234,13 @@ static unsigned int mmc_do_calc_max_discard(struct mmc_card *card,
if (!qty)
return 0;

- if (qty == 1)
- return 1;
-
/* Convert qty to sectors */
if (card->erase_shift)
- max_discard = --qty << card->erase_shift;
+ max_discard = qty << card->erase_shift;
else if (mmc_card_sd(card))
max_discard = qty;
else
- max_discard = --qty * card->erase_size;
+ max_discard = qty * card->erase_size;

return max_discard;
}
--
2.1.4