mtd: spi-nor: spansion: preserve CFR2V[7] when writing MEMLAT

CFR2V[7] is assigned to Flash's address mode (3- or 4-ybte) and must not
be changed when writing MEMLAT (CFR2V[3:0]). CFR2V shall be used in a read,
update, write back fashion.

Fixes: c3266af ("mtd: spi-nor: spansion: add support for Cypress Semper flash")
Signed-off-by: Takahiro Kuwano <Takahiro.Kuwano@infineon.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230726075257.12985-3-tudor.ambarus@linaro.org
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>

Author: Kuwano-san

drivers/mtd/spi-nor/spansion.c

@@ -4,6 +4,7 @@
  * Copyright (C) 2014, Freescale Semiconductor, Inc.
  */
 
+#include <linux/bitfield.h>
 #include <linux/device.h>
 #include <linux/mtd/spi-nor.h>
 
@@ -28,6 +29,7 @@
 #define SPINOR_REG_CYPRESS_CFR2			0x3
 #define SPINOR_REG_CYPRESS_CFR2V					\
 	(SPINOR_REG_CYPRESS_VREG + SPINOR_REG_CYPRESS_CFR2)
+#define SPINOR_REG_CYPRESS_CFR2_MEMLAT_MASK	GENMASK(3, 0)
 #define SPINOR_REG_CYPRESS_CFR2_MEMLAT_11_24	0xb
 #define SPINOR_REG_CYPRESS_CFR2_ADRBYT		BIT(7)
 #define SPINOR_REG_CYPRESS_CFR3			0x4
@@ -161,8 +163,18 @@ static int cypress_nor_octal_dtr_en(struct spi_nor *nor)
 	int ret;
 	u8 addr_mode_nbytes = nor->params->addr_mode_nbytes;
 
+	op = (struct spi_mem_op)
+		CYPRESS_NOR_RD_ANY_REG_OP(addr_mode_nbytes,
+					  SPINOR_REG_CYPRESS_CFR2V, 0, buf);
+
+	ret = spi_nor_read_any_reg(nor, &op, nor->reg_proto);
+	if (ret)
+		return ret;
+
 	/* Use 24 dummy cycles for memory array reads. */
-	*buf = SPINOR_REG_CYPRESS_CFR2_MEMLAT_11_24;
+	*buf &= ~SPINOR_REG_CYPRESS_CFR2_MEMLAT_MASK;
+	*buf |= FIELD_PREP(SPINOR_REG_CYPRESS_CFR2_MEMLAT_MASK,
+			   SPINOR_REG_CYPRESS_CFR2_MEMLAT_11_24);
 	op = (struct spi_mem_op)
 		CYPRESS_NOR_WR_ANY_REG_OP(addr_mode_nbytes,
 					  SPINOR_REG_CYPRESS_CFR2V, 1, buf);