mtd: nand: add sanity check of ecc strength to nand_scan_tail()

This patch adds sanity checks that ensure that drivers for controllers with
hardware ECC set the 'strength' element in struct nand_ecc_ctrl.  Also stylistic
changes to the line that calculates strength for software ECC.

This v2 simplifies the check.  Thanks Brian!¹

¹ http://lists.infradead.org/pipermail/linux-mtd/2012-April/040890.htmlSigned-off-by: Mike Dunn <mikedunn@newsguy.com>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/nand/nand_base.c

@@ -3348,8 +3348,13 @@ int nand_scan_tail(struct mtd_info *mtd)
 		if (!chip->ecc.write_oob)
 			chip->ecc.write_oob = nand_write_oob_syndrome;
 
-		if (mtd->writesize >= chip->ecc.size)
+		if (mtd->writesize >= chip->ecc.size) {
+			if (!chip->ecc.strength) {
+				pr_warn("Driver must set ecc.strength when using hardware ECC\n");
+				BUG();
+			}
 			break;
+		}
 		pr_warn("%d byte HW ECC not possible on "
 			   "%d byte page size, fallback to SW ECC\n",
 			   chip->ecc.size, mtd->writesize);
@@ -3404,7 +3409,7 @@ int nand_scan_tail(struct mtd_info *mtd)
 			BUG();
 		}
 		chip->ecc.strength =
-			chip->ecc.bytes*8 / fls(8*chip->ecc.size);
+			chip->ecc.bytes * 8 / fls(8 * chip->ecc.size);
 		break;
 
 	case NAND_ECC_NONE: