linux-kernel - Re: [PATCH v3 1/2] mmc: block: Issue flush only if allowed

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Date:   Tue, 20 Apr 2021 14:20:30 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Avri Altman <avri.altman@....com>,
        Ulf Hansson <ulf.hansson@...aro.org>, linux-mmc@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Brendan Peter <bpeter@...x.com>
Subject: Re: [PATCH v3 1/2] mmc: block: Issue flush only if allowed

On 20/04/21 8:53 am, Avri Altman wrote:
> The cache may be flushed to the nonvolatile storage by writing to
> FLUSH_CACHE byte (EXT_CSD byte [32]). When in command queueing mode, the
> cache may be flushed by issuing a CMDQ_TASK_ DEV_MGMT (CMD48) with a
> FLUSH_CACHE op-code.  Either way, verify that The cache function is
> turned ON before doing so.
> 
> fixes: 1e8e55b67030 (mmc: block: Add CQE support)
> 
> Reported-by: Brendan Peter <bpeter@...x.com>
> Tested-by: Brendan Peter <bpeter@...x.com>
> Signed-off-by: Avri Altman <avri.altman@....com>
> ---
>  drivers/mmc/core/block.c   | 7 +++++++
>  drivers/mmc/core/mmc.c     | 2 +-
>  drivers/mmc/core/mmc_ops.h | 5 +++++
>  3 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
> index 8bfd4d95b386..5b6501fc9fb7 100644
> --- a/drivers/mmc/core/block.c
> +++ b/drivers/mmc/core/block.c
> @@ -1476,6 +1476,11 @@ static int mmc_blk_cqe_issue_flush(struct mmc_queue *mq, struct request *req)
>  	struct mmc_queue_req *mqrq = req_to_mmc_queue_req(req);
>  	struct mmc_request *mrq = mmc_blk_cqe_prep_dcmd(mqrq, req);
>  
> +	if (mmc_card_mmc(mq->card) && !mmc_flush_allowed(mq->card)) {
> +		blk_mq_end_request(req, BLK_STS_OK);
> +		return -EPERM;
> +	}
> +
>  	mrq->cmd->opcode = MMC_SWITCH;
>  	mrq->cmd->arg = (MMC_SWITCH_MODE_WRITE_BYTE << 24) |
>  			(EXT_CSD_FLUSH_CACHE << 16) |
> @@ -2226,6 +2231,8 @@ enum mmc_issued mmc_blk_mq_issue_rq(struct mmc_queue *mq, struct request *req)
>  		switch (req_op(req)) {
>  		case REQ_OP_FLUSH:
>  			ret = mmc_blk_cqe_issue_flush(mq, req);
> +			if (ret == -EPERM)
> +				return MMC_REQ_FINISHED;

Using an error code for this case seems a little fragile.

How about something like:

 		case REQ_OP_FLUSH:
			if (mmc_blk_cache_disabled(mq->card)) {
				blk_mq_end_request(req, BLK_STS_OK);
				return MMC_REQ_FINISHED;
			}
 			ret = mmc_blk_cqe_issue_flush(mq, req);


static bool mmc_blk_cache_disabled(struct mmc_card *card)
{
	return mmc_card_mmc(mq->card) && !mmc_flush_allowed(card);
}

>  			break;
>  		case REQ_OP_READ:
>  		case REQ_OP_WRITE:
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index 9ad4aa537867..e3da62ffcb5e 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -2037,7 +2037,7 @@ static int _mmc_flush_cache(struct mmc_card *card)
>  {
>  	int err = 0;
>  
> -	if (card->ext_csd.cache_size > 0 && card->ext_csd.cache_ctrl & 1) {
> +	if (mmc_flush_allowed(card)) {
>  		err = mmc_switch(card, EXT_CSD_CMD_SET_NORMAL,
>  				 EXT_CSD_FLUSH_CACHE, 1,
>  				 CACHE_FLUSH_TIMEOUT_MS);
> diff --git a/drivers/mmc/core/mmc_ops.h b/drivers/mmc/core/mmc_ops.h
> index 5782fdf4e8e9..2682bf66708a 100644
> --- a/drivers/mmc/core/mmc_ops.h
> +++ b/drivers/mmc/core/mmc_ops.h
> @@ -19,6 +19,11 @@ enum mmc_busy_cmd {
>  struct mmc_host;
>  struct mmc_card;
>  
> +static inline bool mmc_flush_allowed(struct mmc_card *card)
> +{
> +	return card->ext_csd.cache_size > 0 && card->ext_csd.cache_ctrl & 1;
> +}
> +
>  int mmc_select_card(struct mmc_card *card);
>  int mmc_deselect_cards(struct mmc_host *host);
>  int mmc_set_dsr(struct mmc_host *host);
>