mtd: spi-nor: spansion: write 2 bytes when disabling Octal DTR mode

The Octal DTR configuration is stored in the CFR5V register. This
register is 1 byte wide. But 1 byte long transactions are not allowed in
8D-8D-8D mode. Since the next byte address does not contain any
register, it is safe to write any value to it. Write a 0 to it.
Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20210531181757.19458-3-p.yadav@ti.com

drivers/mtd/spi-nor/spansion.c

@@ -65,10 +65,18 @@ static int spi_nor_cypress_octal_dtr_enable(struct spi_nor *nor, bool enable)
 	if (ret)
 		return ret;
 
-	if (enable)
-		*buf = SPINOR_REG_CYPRESS_CFR5V_OCT_DTR_EN;
-	else
-		*buf = SPINOR_REG_CYPRESS_CFR5V_OCT_DTR_DS;
+	if (enable) {
+		buf[0] = SPINOR_REG_CYPRESS_CFR5V_OCT_DTR_EN;
+	} else {
+		/*
+		 * The register is 1-byte wide, but 1-byte transactions are not
+		 * allowed in 8D-8D-8D mode. Since there is no register at the
+		 * next location, just initialize the value to 0 and let the
+		 * transaction go on.
+		 */
+		buf[0] = SPINOR_REG_CYPRESS_CFR5V_OCT_DTR_DS;
+		buf[1] = 0;
+	}
 
 	op = (struct spi_mem_op)
 		SPI_MEM_OP(SPI_MEM_OP_CMD(SPINOR_OP_WR_ANY_REG, 1),
@@ -76,7 +84,7 @@ static int spi_nor_cypress_octal_dtr_enable(struct spi_nor *nor, bool enable)
 					   SPINOR_REG_CYPRESS_CFR5V,
 					   1),
 			   SPI_MEM_OP_NO_DUMMY,
-			   SPI_MEM_OP_DATA_OUT(1, buf, 1));
+			   SPI_MEM_OP_DATA_OUT(enable ? 1 : 2, buf, 1));
 
 	if (!enable)
 		spi_nor_spimem_setup_op(nor, &op, SNOR_PROTO_8_8_8_DTR);