From: Stephen Warren <swarren@xxxxxxxxxx> 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.hunter@xxxxxxxxx> Cc: Dong Aisheng <dongas86@xxxxxxxxx> Cc: Ulf Hansson <ulf.hansson@xxxxxxxxxx> Cc: Vladimir Zapolskiy <vz@xxxxxxxxx> Fixes: e056a1b5b67b "(mmc: queue: let host controllers specify maximum discard timeout") Signed-off-by: Stephen Warren <swarren@xxxxxxxxxx> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
