Re: [v5 2/5] MMC: Use CMD23 for multiblock transfers when we can.

From: Andrei Warkentin <andreiw@motorola.com>
To: Jaehoon Chung <jh80.chung@samsung.com>
Cc: linux-mmc@vger.kernel.org, cjb@laptop.org, arindam.nath@amd.com,
	arnd@arndb.de, malchev@google.com,
	Kyungmin Park <kyungmin.park@samsung.com>
Subject: Re: [v5 2/5] MMC: Use CMD23 for multiblock transfers when we can.
Date: Fri, 20 May 2011 13:12:07 -0500	[thread overview]
Message-ID: <BANLkTimyCO1vwjG5jnYVg+Yb=eLr6+C6hQ@mail.gmail.com> (raw)
In-Reply-To: <4DD642A0.1040608@samsung.com>

On Fri, May 20, 2011 at 5:29 AM, Jaehoon Chung <jh80.chung@samsung.com> wrote:
> Hi Andrei.
>
> I have some question..
> In mmc_blk_issue_rw_rq() of block.c, there is the below code.
>
> static int mmc_blk_issue_rw_rq(struct mmc_queue *mq, struct request *req)
> {
>        struct mmc_blk_data *md = mq->data;
>        struct mmc_card *card = md->queue.card;
>        struct mmc_blk_request brq;
>        int ret = 1, disable_multi = 0;
>
>        /*
>         * Reliable writes are used to implement Forced Unit Access and
>         * REQ_META accesses, and are supported only on MMCs.
>         */
>        bool do_rel_wr = ((req->cmd_flags & REQ_FUA) ||
>                          (req->cmd_flags & REQ_META)) &&
>                (rq_data_dir(req) == WRITE) &&
>                REL_WRITES_SUPPORTED(card);
>
>        do {
>                struct mmc_command cmd = {0};
>                u32 readcmd, writecmd, status = 0;
>
>                memset(&brq, 0, sizeof(struct mmc_blk_request));
>                brq.mrq.cmd = &brq.cmd;
>                brq.mrq.data = &brq.data;
>
>                brq.cmd.arg = blk_rq_pos(req);
>                if (!mmc_card_blockaddr(card))
>                        brq.cmd.arg <<= 9;
>                brq.cmd.flags = MMC_RSP_SPI_R1 | MMC_RSP_R1 | MMC_CMD_ADTC;
>                brq.data.blksz = 512;
>                brq.stop.opcode = MMC_STOP_TRANSMISSION;
>                brq.stop.arg = 0;
>                brq.stop.flags = MMC_RSP_SPI_R1B | MMC_RSP_R1B | MMC_CMD_AC;
>                brq.data.blocks = blk_rq_sectors(req);
>
> There is "brq.stop.opcode = MMC_STOP_TRANSMISSION".
> If we use CMD23, this line didn't need? Actually i don't know, so i ask to you.
>

Nope. Needed. CMD23 support might not be implemented by host driver
(like it isn't right now for anything non-SDHCI). And even it if were,
you still need to send stop command on any error conditions. I suggest
you read the relevant sections in the publically available eMMC spec.

A