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.pdf

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Dave Hylands <dhylands@gmail.com>
Tested-by: Steve Sakoman <sakoman@gmail.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

2 files changed, 15 insertions, 7 deletions

diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index c0cb225bbb47..a1cb21f95302 100644
--- a/drivers/mmc/card/block.c
+++ b/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
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 16e9338944e8..a3ac9c48e5de 100644
--- a/include/linux/mmc/host.h
+++ b/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;