mmc: core: enable CMD19 tuning for DDR50 mode

As SD Specifications Part1 Physical Layer Specification Version
3.01 says, CMD19 tuning is available for unlocked cards in transfer
state of 1.8V signaling mode. The small difference between v3.00
and 3.01 spec means that CMD19 tuning is also available for DDR50
mode.

Signed-off-by: Weijun Yang <york.yang@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/sd.c

@@ -627,8 +627,24 @@ static int mmc_sd_init_uhs_card(struct mmc_card *card)
 	 */
 	if (!mmc_host_is_spi(card->host) &&
 		(card->sd_bus_speed == UHS_SDR50_BUS_SPEED ||
-	     card->sd_bus_speed == UHS_SDR104_BUS_SPEED))
+		 card->sd_bus_speed == UHS_DDR50_BUS_SPEED ||
+		 card->sd_bus_speed == UHS_SDR104_BUS_SPEED)) {
 		err = mmc_execute_tuning(card);
+
+		/*
+		 * As SD Specifications Part1 Physical Layer Specification
+		 * Version 3.01 says, CMD19 tuning is available for unlocked
+		 * cards in transfer state of 1.8V signaling mode. The small
+		 * difference between v3.00 and 3.01 spec means that CMD19
+		 * tuning is also available for DDR50 mode.
+		 */
+		if (err && card->sd_bus_speed == UHS_DDR50_BUS_SPEED) {
+			pr_warn("%s: ddr50 tuning failed\n",
+				mmc_hostname(card->host));
+			err = 0;
+		}
+	}
+
 out:
 	kfree(status);