mmc: block: avoid multiblock reads for the last sector in SPI mode

On some SD cards over SPI, reading with the multiblock read command the last
sector will leave the card in a bad state.

Remove last sectors from the multiblock reading cmd.
Signed-off-by: Chris Boot <bootc@bootc.net>
Signed-off-by: Clément Péron <peron.clem@gmail.com>
Cc: stable@vger.kernel.org # v4.10+
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/block.c

@@ -1370,6 +1370,16 @@ static void mmc_blk_data_prep(struct mmc_queue *mq, struct mmc_queue_req *mqrq,
 		brq->data.blocks = card->host->max_blk_count;
 
 	if (brq->data.blocks > 1) {
+		/*
+		 * Some SD cards in SPI mode return a CRC error or even lock up
+		 * completely when trying to read the last block using a
+		 * multiblock read command.
+		 */
+		if (mmc_host_is_spi(card->host) && (rq_data_dir(req) == READ) &&
+		    (blk_rq_pos(req) + blk_rq_sectors(req) ==
+		     get_capacity(md->disk)))
+			brq->data.blocks--;
+
 		/*
 		 * After a read error, we redo the request one sector
 		 * at a time in order to accurately determine which