mtd: nand: omap: ecc.correct: omap_elm_correct_data: fix programmed-page bit-flip correction logic

This patch updates following checks when bit-flips are detected by ELM:

 - Do not evaluate bit-flips when un-correctable bit-flips is reported by ELM,
   because as per [1] when ELM reports an un-correctable bit-flips,
   'number of error' field in its ELM_LOCATION_STATUS register is also invalid.

 - Return with error-code '-EBADMSG' on detection of un-correctable bit-flip.

 - Return with error-code '-EBADMSG' when bit-flips position is outside current
   Sector and OOB area.

[1] ELM IP spec Table-25 ELM_LOCATION_STATUS Register.
    ELM_LOCATION_STATUS[8] = ECC_CORRECTABLE: Error location process exit status
        0x0: ECC error location process failed.
             Number of errors and error locations are invalid.
        0x1: all errors were successfully located.
             Number of errors and error locations are valid.
Tested-by: Stefan Roese <sr@denx.de>
Signed-off-by: Pekon Gupta <pekon@ti.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/nand/omap2.c

@@ -1353,6 +1353,7 @@ static int omap_elm_correct_data(struct mtd_info *mtd, u_char *data,
 	int bitflip_count;
 	bool is_error_reported = false;
 	u32 bit_pos, byte_pos, error_max, pos;
+	int err;
 
 	switch (info->ecc_opt) {
 	case OMAP_ECC_BCH4_CODE_HW:
@@ -1434,8 +1435,12 @@ static int omap_elm_correct_data(struct mtd_info *mtd, u_char *data,
 	/* Decode BCH error using ELM module */
 	elm_decode_bch_error_page(info->elm_dev, ecc_vec, err_vec);
 
+	err = 0;
 	for (i = 0; i < eccsteps; i++) {
-		if (err_vec[i].error_reported) {
+		if (err_vec[i].error_uncorrectable) {
+			pr_err("nand: uncorrectable bit-flips found\n");
+			err = -EBADMSG;
+		} else if (err_vec[i].error_reported) {
 			for (j = 0; j < err_vec[i].error_count; j++) {
 				switch (info->ecc_opt) {
 				case OMAP_ECC_BCH4_CODE_HW:
@@ -1457,13 +1462,22 @@ static int omap_elm_correct_data(struct mtd_info *mtd, u_char *data,
 				byte_pos = (error_max - pos - 1) / 8;
 
 				if (pos < error_max) {
-					if (byte_pos < 512)
+					if (byte_pos < 512) {
+						pr_debug("bitflip@dat[%d]=%x\n",
+						     byte_pos, data[byte_pos]);
 						data[byte_pos] ^= 1 << bit_pos;
-					else
+					} else {
+						pr_debug("bitflip@oob[%d]=%x\n",
+							(byte_pos - 512),
+						     spare_ecc[byte_pos - 512]);
 						spare_ecc[byte_pos - 512] ^=
 							1 << bit_pos;
+					}
+				} else {
+					pr_err("invalid bit-flip @ %d:%d\n",
+							 byte_pos, bit_pos);
+					err = -EBADMSG;
 				}
-				/* else, not interested to correct ecc */
 			}
 		}
 
@@ -1475,12 +1489,7 @@ static int omap_elm_correct_data(struct mtd_info *mtd, u_char *data,
 		spare_ecc += ecc->bytes;
 	}
 
-	for (i = 0; i < eccsteps; i++)
-		/* Return error if uncorrectable error present */
-		if (err_vec[i].error_uncorrectable)
-			return -EINVAL;
-
-	return stat;
+	return (err) ? err : stat;
 }
 
 /**