On Tue, Dec 13, 2016 at 11:19 PM, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: > On 13/12/16 21:20, Gwendal Grignou wrote: >> Working with a SDHCI controller and a Toshiba 16GB THGBMFG7C2LBAIL. >> The Toshiba part has a large erase group size and a long erase timeout. >> It barely fits within the controller timeout, but mmc reports a >> 512B discard size to the block layer instead of the expected 4MB: >> /sys/block/mmcblk0/queue/discard_max_bytes = 512 >> >> The host caps[0] is 0x...b2, so host->max_busy_timeout is set to >> 2684.35ms: (1 << 27 / ((0xb2 & 0x3f) * 1000). >> >> In Toshiba EXT_CSD, HC_ERASE_GRP_SIZE is set to 7 (2100ms erase timeout) >> HC_ERASE_GRP_SIZE is set to 8, (8192 512B sectors erase size). >> >> In mmc_do_calc_max_discard(), as a safety, for eMMC device, number of >> erase groups that could safely be erased with the host timeout (qty) was >> reduced by 1. > > It was not for safety - it was to allow for crossing an erase group boundary. Got it. > > But the current code is quite different now, so please have a look at that > because this code does not apply anymore. Indeed, looking at the block layer, it is paying attention not to cross boundary, issuing an extra erase command when necessary. in blkdev_issue_discard(), we use bdev_discard_alignment to be sure erasing within a partition still start on a erase group boundary. It has been addressed with c6e66634 (block: split discard into aligned requests) and following changes. > -- 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
