mmc: core: add workaround for controllers with broken multiblock reads

Due to hardware bugs, some MMC host controllers don't support
multiple-block reads[1].  To resolve, add a new MMC capability flag,
MMC_CAP2_NO_MULTI_READ, which can be set by affected host controller
drivers.  When this capability is set, all reads will be issued one
sector at a time.

1. See for example Advisory 2.1.1.128 "MMC: Multiple Block Read
Operation Issue" in _OMAP3530/3525/3515/3503 Silicon Errata_
Revision F (October 2010) (SPRZ278F), available from
http://focus.ti.com/lit/er/sprz278f/sprz278f.pdfSigned-off-by: NPaul Walmsley <paul@pwsan.com>
Cc: Dave Hylands <dhylands@gmail.com>
Tested-by: NSteve Sakoman <sakoman@gmail.com>
Signed-off-by: NChris Ball <cjb@laptop.org>

drivers/mmc/card/block.c

@@ -1030,13 +1030,20 @@ static void mmc_blk_rw_rq_prep(struct mmc_queue_req *mqrq,
 	if (brq->data.blocks > card->host->max_blk_count)
 		brq->data.blocks = card->host->max_blk_count;
 
-	/*
-	 * After a read error, we redo the request one sector at a time
-	 * in order to accurately determine which sectors can be read
-	 * successfully.
-	 */
-	if (disable_multi && brq->data.blocks > 1)
-		brq->data.blocks = 1;
+	if (brq->data.blocks > 1) {
+		/*
+		 * After a read error, we redo the request one sector
+		 * at a time in order to accurately determine which
+		 * sectors can be read successfully.
+		 */
+		if (disable_multi)
+			brq->data.blocks = 1;
+
+		/* Some controllers can't do multiblock reads due to hw bugs */
+		if (card->host->caps2 & MMC_CAP2_NO_MULTI_READ &&
+		    rq_data_dir(req) == READ)
+			brq->data.blocks = 1;
+	}
 
 	if (brq->data.blocks > 1 || do_rel_wr) {
 		/* SPI multiblock writes terminate using a special

include/linux/mmc/host.h

@@ -241,6 +241,7 @@ struct mmc_host {
 #define MMC_CAP2_BOOTPART_NOACC	(1 << 0)	/* Boot partition no access */
 #define MMC_CAP2_CACHE_CTRL	(1 << 1)	/* Allow cache control */
 #define MMC_CAP2_POWEROFF_NOTIFY (1 << 2)	/* Notify poweroff supported */
+#define MMC_CAP2_NO_MULTI_READ	(1 << 3)	/* Multiblock reads don't work */
 
 	mmc_pm_flag_t		pm_caps;	/* supported pm features */
 	unsigned int        power_notify_type;