mmc: Allow forward compatibility for eMMC

As stated by the eMMC 5.0 specification, a chip should not be rejected
only because of the revision stated in the EXT_CSD_REV field of the
EXT_CSD register.

Remove the control on this value, the control of the CSD_STRUCTURE field
should be sufficient to reject future incompatible changes.
Signed-off-by: Romain Izard <romain.izard.pro@gmail.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/mmc.c

@@ -324,13 +324,12 @@ static int mmc_read_ext_csd(struct mmc_card *card, u8 *ext_csd)
 		}
 	}
 
+	/*
+	 * The EXT_CSD format is meant to be forward compatible. As long
+	 * as CSD_STRUCTURE does not change, all values for EXT_CSD_REV
+	 * are authorized, see JEDEC JESD84-B50 section B.8.
+	 */
 	card->ext_csd.rev = ext_csd[EXT_CSD_REV];
-	if (card->ext_csd.rev > 7) {
-		pr_err("%s: unrecognised EXT_CSD revision %d\n",
-			mmc_hostname(card->host), card->ext_csd.rev);
-		err = -EINVAL;
-		goto out;
-	}
 
 	card->ext_csd.raw_sectors[0] = ext_csd[EXT_CSD_SEC_CNT + 0];
 	card->ext_csd.raw_sectors[1] = ext_csd[EXT_CSD_SEC_CNT + 1];