mmc: Add .multi_io_quirk callback for multi I/O HW bug

Historically, we have been using MMC_CAP* to handle host HW issues and
currently the block layer uses MMC_CAP2_NO_MULTI_READ flag for a multi
I/O HW bug workaround.

There are a few tweaks needed to make MMC_CAP2_NO_MULTI_READ suite all
situations. Therefore let's add an optional host ops callback to enable
host drivers to return the number of blocks it allows per request.

In a future patch and when host drivers have converted to the new
callback, MMC_CAP2_NO_MULTI_READ shall be removed.
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/card/block.c

@@ -1402,6 +1402,16 @@ static void mmc_blk_rw_rq_prep(struct mmc_queue_req *mqrq,
 		if (card->host->caps2 & MMC_CAP2_NO_MULTI_READ &&
 		    rq_data_dir(req) == READ)
 			brq->data.blocks = 1;
+
+		/*
+		 * Some controllers have HW issues while operating
+		 * in multiple I/O mode
+		 */
+		if (card->host->ops->multi_io_quirk)
+			brq->data.blocks = card->host->ops->multi_io_quirk(card,
+						(rq_data_dir(req) == READ) ?
+						MMC_DATA_READ : MMC_DATA_WRITE,
+						brq->data.blocks);
 	}
 
 	if (brq->data.blocks > 1 || do_rel_wr) {

include/linux/mmc/host.h

@@ -139,6 +139,13 @@ struct mmc_host_ops {
 	int	(*select_drive_strength)(unsigned int max_dtr, int host_drv, int card_drv);
 	void	(*hw_reset)(struct mmc_host *host);
 	void	(*card_event)(struct mmc_host *host);
+
+	/*
+	 * Optional callback to support controllers with HW issues for multiple
+	 * I/O. Returns the number of supported blocks for the request.
+	 */
+	int	(*multi_io_quirk)(struct mmc_card *card,
+				  unsigned int direction, int blk_size);
 };
 
 struct mmc_card;