On 28 January 2017 at 09:16, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: > On 27/01/2017 5:12 p.m., Ulf Hansson wrote: >> >> On 26 January 2017 at 13:39, Adrian Hunter <adrian.hunter@xxxxxxxxx> >> wrote: >>> >>> On 26/01/17 12:50, Ulf Hansson wrote: >>>> >>>> On 11 January 2017 at 18:19, Gregory CLEMENT >>>> <gregory.clement@xxxxxxxxxxxxxxxxxx> wrote: >>>>> >>>>> + priv->init_card_type = MMC_TYPE_MMC; >>>>> + mmc->caps |= MMC_CAP_NONREMOVABLE; >>>>> + >>>>> + /* >>>>> + * Force to clear BUS_TEST to >>>>> + * skip bus_test_pre and bus_test_post >>>>> + */ >>>>> + mmc->caps &= ~MMC_CAP_BUS_WIDTH_TEST; >>>>> + mmc->caps2 |= MMC_CAP2_HC_ERASE_SZ | >>>> >>>> >>>> This cap is a bit strange. It was added several years ago by Adrian >>>> Hunter, but I am wondering about the reason to why it's needed. >>>> >>> >>> MMC_CAP2_HC_ERASE_SZ relates to EXT-CSD ERASE_GROUP_DEF. >>> >>> I think it was added to enable people to choose whether they wanted a >>> large >>> or small erase granularity. That probably doesn't matter if the card >>> supports TRIM. >>> >> >> Huh, the erase/trim/discard code in the mmc core is really hairy. :-) >> >> In mmc_calc_max_discard() the following code/comment exists: >> >> /* >> * Without erase_group_def set, MMC erase timeout depends on clock >> * frequence which can change. In that case, the best choice is >> * just the preferred erase size. >> */ >> if (mmc_card_mmc(card) && !(card->ext_csd.erase_group_def & 1)) >> return card->pref_erase; >> >> >> This makes me wonder. >> >> So, when we haven't enabled the high capacity erase groups in the >> EXT_CSD register (ext_csd.erase_group_def), we will use the pref_erase >> size. >> >> In the other case, as when having MMC_CAP2_HC_ERASE_SZ set (which will >> set ext_csd.erase_group_def), we will instead do some calculations >> to find out the max discards. >> >> Are you saying that these calculations doesn't matter much - or are >> you saying that we always want to do them? > > > No, I was saying that if you have TRIM then TRIM is preferred to ERASE so > the erase group size does not come into play when discarding, since ERASE > granularity is erase groups whereas TRIM granularity is sectors. Right. Thanks for clarifying. > > However ERASE_GROUP_DEF also affects the size of write protect groups. In either case. What do you think of removing MMC_CAP2_HC_ERASE_SZ? I don't like these kind of soft polices, it's better if we can decide on a common behaviour - whatever that is. Kind regards Uffe -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
