RE: [PATCH] mmc: core: support zeroout using TRIM

[Avri Altman <Avri.Altman@wdc.com>]

> If the device supports TRIM and indicates that it erases to zeros, we can use
> it to support hardware offloading of REQ_OP_WRITE_ZEROES.
> 
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
I agree that zero out is indeed a privet case of trim, as indicated by ERASED_MEM_CONT.

Looks good to me.

Thanks,
Avri

> ---
> 
> Notes:
>     https://lore.kernel.org/lkml/20160303182146.GG9772@thunk.org/ seems
> to agree
>     that BLKZEROOUT can use TRIM on eMMC.
> 
>     BLKDISCARD uses DISCARD when available so it can't be used to send
> TRIM.
> 
>     If TRIM should not be used for BLKZEROOUT for some reason I guess the
> only way
>     is to use MMC_IOC_MULTI_CMD like in this commit in mmc-utils but
> that's a
>     rather low-level interface:
> 
>      https://git.kernel.org/pub/scm/utils/mmc/mmc-
> utils.git/commit/?id=43282e80e174cc73b09b81a4d17cb3a7b4dc5cfc
> 
>  drivers/mmc/core/block.c | 26 ++++++++++++++++++++++----
> drivers/mmc/core/queue.c |  2 ++
>  2 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c index
> 506dc900f5c7..0398b205a285 100644
> --- a/drivers/mmc/core/block.c
> +++ b/drivers/mmc/core/block.c
> @@ -126,6 +126,7 @@ struct mmc_blk_data {
>  #define MMC_BLK_DISCARD                BIT(2)
>  #define MMC_BLK_SECDISCARD     BIT(3)
>  #define MMC_BLK_CQE_RECOVERY   BIT(4)
> +#define MMC_BLK_TRIM           BIT(5)
> 
>         /*
>          * Only set in main mmc_blk_data associated @@ -1090,12 +1091,13
> @@ static void mmc_blk_issue_drv_op(struct mmc_queue *mq, struct
> request *req)
>         blk_mq_end_request(req, ret ? BLK_STS_IOERR : BLK_STS_OK);  }
> 
> -static void mmc_blk_issue_discard_rq(struct mmc_queue *mq, struct
> request *req)
> +static void mmc_blk_issue_erase_rq(struct mmc_queue *mq, struct
> request *req,
> +                                  int type, unsigned int erase_arg)
>  {
>         struct mmc_blk_data *md = mq->blkdata;
>         struct mmc_card *card = md->queue.card;
>         unsigned int from, nr;
> -       int err = 0, type = MMC_BLK_DISCARD;
> +       int err = 0;
>         blk_status_t status = BLK_STS_OK;
> 
>         if (!mmc_can_erase(card)) {
> @@ -1111,13 +1113,13 @@ static void mmc_blk_issue_discard_rq(struct
> mmc_queue *mq, struct request *req)
>                 if (card->quirks & MMC_QUIRK_INAND_CMD38) {
>                         err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
>                                          INAND_CMD38_ARG_EXT_CSD,
> -                                        card->erase_arg == MMC_TRIM_ARG ?
> +                                        erase_arg == MMC_TRIM_ARG ?
>                                          INAND_CMD38_ARG_TRIM :
>                                          INAND_CMD38_ARG_ERASE,
>                                          card->ext_csd.generic_cmd6_time);
>                 }
>                 if (!err)
> -                       err = mmc_erase(card, from, nr, card->erase_arg);
> +                       err = mmc_erase(card, from, nr, erase_arg);
>         } while (err == -EIO && !mmc_blk_reset(md, card->host, type));
>         if (err)
>                 status = BLK_STS_IOERR;
> @@ -1127,6 +1129,19 @@ static void mmc_blk_issue_discard_rq(struct
> mmc_queue *mq, struct request *req)
>         blk_mq_end_request(req, status);  }
> 
> +static void mmc_blk_issue_trim_rq(struct mmc_queue *mq, struct request
> +*req) {
> +       mmc_blk_issue_erase_rq(mq, req, MMC_BLK_TRIM, MMC_TRIM_ARG);
> }
> +
> +static void mmc_blk_issue_discard_rq(struct mmc_queue *mq, struct
> +request *req) {
> +       struct mmc_blk_data *md = mq->blkdata;
> +       struct mmc_card *card = md->queue.card;
> +
> +       mmc_blk_issue_erase_rq(mq, req, MMC_BLK_DISCARD,
> +card->erase_arg); }
> +
>  static void mmc_blk_issue_secdiscard_rq(struct mmc_queue *mq,
>                                        struct request *req)  { @@ -2327,6 +2342,9 @@ enum
> mmc_issued mmc_blk_mq_issue_rq(struct mmc_queue *mq, struct request
> *req)
>                 case REQ_OP_SECURE_ERASE:
>                         mmc_blk_issue_secdiscard_rq(mq, req);
>                         break;
> +               case REQ_OP_WRITE_ZEROES:
> +                       mmc_blk_issue_trim_rq(mq, req);
> +                       break;
>                 case REQ_OP_FLUSH:
>                         mmc_blk_issue_flush(mq, req);
>                         break;
> diff --git a/drivers/mmc/core/queue.c b/drivers/mmc/core/queue.c index
> c69b2d9df6f1..bbe2ea829ea7 100644
> --- a/drivers/mmc/core/queue.c
> +++ b/drivers/mmc/core/queue.c
> @@ -191,6 +191,8 @@ static void mmc_queue_setup_discard(struct
> request_queue *q,
>                 q->limits.discard_granularity = SECTOR_SIZE;
>         if (mmc_can_secure_erase_trim(card))
>                 blk_queue_flag_set(QUEUE_FLAG_SECERASE, q);
> +       if (mmc_can_trim(card) && card->erased_byte == 0)
> +               blk_queue_max_write_zeroes_sectors(q, max_discard);
>  }
> 
>  static unsigned short mmc_get_max_segments(struct mmc_host *host)
> --
> 2.34.1