From: Stephen Warren <swar...@nvidia.com>
In mmc_do_calc_max_discard(), if only a single erase block can be
discarded within the host controller's timeout, don't allow discard
operations at all.
Previously, the code allowed sector-at-a-time discard (rather than
erase-block-at-a-time), which was chronically slow.
Without this patch, on the NVIDIA Tegra Cardhu board, the loops result
in qty == 1, which is immediately returned. This causes discard to
operate a single sector at a time, which is chronically slow. With this
patch in place, discard operates a single erase block at a time, which
is reasonably fast.
Cc: Adrian Hunter <adrian.hun...@intel.com>
Cc: Dong Aisheng <donga...@gmail.com>
Cc: Ulf Hansson <ulf.hans...@linaro.org>
Cc: Vladimir Zapolskiy <v...@mleia.com>
Fixes: e056a1b5b67b "(mmc: queue: let host controllers specify maximum discard
timeout")
Signed-off-by: Stephen Warren <swar...@nvidia.com>
---
drivers/mmc/core/core.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 57a2b403bf8e..eb952ca634ea 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -2150,8 +2150,25 @@ static unsigned int mmc_do_calc_max_discard(struct
mmc_card *card,
if (!qty)
return 0;
- if (qty == 1)
- return 1;
+ /*
+ * Discard operations may not be aligned to an erase block. In an
+ * unaligned case, we need to issue 1 more discard operation to HW
+ * than strictly calculated by:
+ * sectors_to_erase / sectors_per_discard_operation
+ *
+ * To account for this in the timeout calculations, we assume we can
+ * actually discard one less erase block than fits into the HW
+ * timeout. This explains the --qty below.
+ *
+ * When only a single discard block operation fits into the timeout,
+ * disallow any discard operations at all. For example, discarding one
+ * sector at a time is so chronically slow as to be useless. However,
+ * make an exception for SD cards without an erase shift, since qty
+ * isn't multiplied up by an erase block size in the code below for
+ * that case.
+ */
+ if (qty == 1 && !(!card->erase_shift && mmc_card_sd(card)))
+ return 0;
/* Convert qty to sectors */
if (card->erase_shift)
--
1.8.1.5
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