On 17/12/13 20:02, Stephen Warren wrote: > From: Stephen Warren <[email protected]> > > In mmc_do_calc_max_discard(), if any value has been assigned to qty, > that value must have passed the timeout checks in the loop. Hence, > qty is the maximum number of erase blocks that fit within the timeout, > not the first value that does not fit into the timeout. In turn, this > means we don't need any special case for (qty == 1); any value of qty > needs to be multiplied by the card's erase shift, and we don't need to > decrement qty before doing so. > > 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 <[email protected]> > Cc: Dong Aisheng <[email protected]> > Cc: Ulf Hansson <[email protected]> > Cc: Vladimir Zapolskiy <[email protected]> > Fixes: e056a1b5b67b "(mmc: queue: let host controllers specify maximum > discard timeout") > Signed-off-by: Stephen Warren <[email protected]> > --- > If this makes sense, I wonder if it should be Cc: stable? > --- > 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 57a2b403bf8e..dd793cf4ef46 100644 > --- a/drivers/mmc/core/core.c > +++ b/drivers/mmc/core/core.c > @@ -2150,16 +2150,13 @@ 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; > } >
The quantity is decreased by 1 to account for the fact that the erase can cross the boundary between 1 erase block and another. i.e. even though the size is 1 erase block it touches 2 erase blocks. -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
