On Thu, Jun 2, 2016 at 5:27 PM, Gwendal Grignou <gwendal@xxxxxxxxxxxx> wrote:
> If available, eMMC stack uses HC_ERASE_GRP_SIZE as preferred erase size.
> However, that size is the minimal size we must use, not the optimal size.
> Calculate the optimal size based on whole device size and fall back to
> HC_ERASE_GRP_SIZE if too small.
>
> Signed-off-by: Gwendal Grignou <gwendal@xxxxxxxxxxxx>
> ---
> v2: fix comments
>
> drivers/mmc/core/core.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index ef76b1c..b858907 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -1987,17 +1987,17 @@ void mmc_init_erase(struct mmc_card *card)
> * to that size and alignment.
> *
> * For SD cards that define Allocation Unit size, limit erases to one
> - * Allocation Unit at a time. For MMC cards that define High Capacity
> - * Erase Size, whether it is switched on or not, limit to that size.
> - * Otherwise just have a stab at a good value. For modern cards it
> - * will end up being 4MiB. Note that if the value is too small, it
> - * can end up taking longer to erase.
> + * Allocation Unit at a time.
> + * For MMC, have a stab at a good value. For modern cards it
> + * will end up being 4MiB.
> + * Be sure the size is at least the High Capacity Erase Size, as long
> + * as it is defined, even if not used.
> + * Note that if the value is too small, it can end up taking longer to
> + * erase.
The last sentence is a key point.
I want to point out the difference in erasing ~23GB of a 32GB device
as specified by the number of secure erase commands sent:
~44K commands (default: single erase block): ~30 minutes
~700 commands (32MB chunks) : ~90 seconds
1 command: < 6 seconds
cheers,
grant
> */
> if (mmc_card_sd(card) && card->ssr.au) {
> card->pref_erase = card->ssr.au;
> card->erase_shift = ffs(card->ssr.au) - 1;
> - } else if (card->ext_csd.hc_erase_size) {
> - card->pref_erase = card->ext_csd.hc_erase_size;
> } else if (card->erase_size) {
> sz = (card->csd.capacity << (card->csd.read_blkbits - 9)) >> 11;
> if (sz < 128)
> @@ -2015,6 +2015,8 @@ void mmc_init_erase(struct mmc_card *card)
> if (sz)
> card->pref_erase += card->erase_size - sz;
> }
> + if (card->ext_csd.hc_erase_size > card->pref_erase)
> + card->pref_erase = card->ext_csd.hc_erase_size;
> } else
> card->pref_erase = 0;
> }
> --
> 2.8.0.rc3.226.g39d4020
>
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