mtd: nand: don't use read_buf for 8-bit ONFI transfers

Use a repeated read_byte() instead of read_buf(), since for x16 buswidth
devices, we need to avoid the upper I/O[16:9] bits. See the following
commit for reference:

commit 05f7835975dad6b3b517f9e23415985e648fb875
Author: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Date:   Thu Dec 5 22:22:04 2013 +0100

    mtd: nand: don't use {read,write}_buf for 8-bit transfers

Now, I think that all barriers to probing ONFI on x16 devices are
removed, so remove the check from nand_flash_detect_onfi().

Tested on 8-bit ONFI NAND (Micron MT29F32G08CBADAWP).

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Tested-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Tested-By: Pekon Gupta <pekon@ti.com>

drivers/mtd/nand/nand_base.c

@@ -3065,7 +3065,7 @@ static int nand_flash_detect_onfi(struct mtd_info *mtd, struct nand_chip *chip,
 					int *busw)
 {
 	struct nand_onfi_params *p = &chip->onfi_params;
-	int i;
+	int i, j;
 	int val;
 
 	/* Try ONFI for unknown chip or LP */
@@ -3074,18 +3074,10 @@ static int nand_flash_detect_onfi(struct mtd_info *mtd, struct nand_chip *chip,
 		chip->read_byte(mtd) != 'F' || chip->read_byte(mtd) != 'I')
 		return 0;
 
-	/*
-	 * ONFI must be probed in 8-bit mode or with NAND_BUSWIDTH_AUTO, not
-	 * with NAND_BUSWIDTH_16
-	 */
-	if (chip->options & NAND_BUSWIDTH_16) {
-		pr_err("ONFI cannot be probed in 16-bit mode; aborting\n");
-		return 0;
-	}
-
 	chip->cmdfunc(mtd, NAND_CMD_PARAM, 0, -1);
 	for (i = 0; i < 3; i++) {
-		chip->read_buf(mtd, (uint8_t *)p, sizeof(*p));
+		for (j = 0; j < sizeof(*p); j++)
+			((uint8_t *)p)[j] = chip->read_byte(mtd);
 		if (onfi_crc16(ONFI_CRC_BASE, (uint8_t *)p, 254) ==
 				le16_to_cpu(p->crc)) {
 			break;