[PATCH linux-next v2 04/14] mtd: spi-nor: fix support of Macronix memories

[Cyrille Pitchen <cyrille.pitchen@atmel.com>]

This patch fixes the support of Macronix memories. Especially we avoid
updating the Status Register when not needed as the Quad Enable (QE) bit
is a non-volatile bit.

Also we add comments to explain why we use some Fast Read op codes rather
than others.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
---
 drivers/mtd/spi-nor/spi-nor.c | 81 ++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 72 insertions(+), 9 deletions(-)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index 8793cebbe5a9..042ac49d6188 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -1115,6 +1115,11 @@ static int macronix_quad_enable(struct spi_nor *nor)
 	val = read_sr(nor);
 	if (val < 0)
 		return val;
+
+	if (likely(val & SR_QUAD_EN_MX))
+		return 0;
+	dev_warn(nor->dev, "Macronix Quad mode disabled, enable it\n");
+
 	write_enable(nor);
 
 	write_sr(nor, val | SR_QUAD_EN_MX);
@@ -1169,21 +1174,73 @@ static int spansion_quad_enable(struct spi_nor *nor)
 	return 0;
 }
 
+static int macronix_set_quad_mode(struct spi_nor *nor)
+{
+	int status;
+
+	/* Check whether the QPI mode is enabled. */
+	if (nor->read_proto == SNOR_PROTO_4_4_4) {
+		/*
+		 * Since the QPI mode is enabled, the Quad Enabled (QE)
+		 * non-volatile bit is already set.
+		 * However in QPI mode, only the Fast Read 1-4-4 (0xeb)
+		 * op code is supported.
+		 * WARNING: we should take care about the performance
+		 * enhance toggling bits P0-P7 written during the
+		 * dummy/mode cycles to avoid entering the continuous
+		 * read (performance enhance) mode by mistake!
+		 */
+		nor->read_opcode = SPINOR_OP_READ_1_4_4;
+		return 0;
+	}
+
+	/*
+	 * The QPI mode is disabled but we still need to set the QE bit:
+	 * this disables the reset and write protect features and
+	 * frees the associated pins so they can be used as the 3rd
+	 * and 4th I/O lines required by Quad SPI commands.
+	 * Also we'd rather use the Fast Read 1-1-4 (0x6b) op code than
+	 * the Fast Read 1-4-4 (0xeb) op code so we don't care about
+	 * entering the continuous read mode by mistake if some
+	 * performance enhance toggling bits P0-P7 were written during
+	 * dummy/mode cycles.
+	 */
+	status = macronix_quad_enable(nor);
+	if (status) {
+		dev_err(nor->dev, "Macronix quad-read not enabled\n");
+		return status;
+	}
+	nor->read_proto = SNOR_PROTO_1_1_4;
+	nor->read_opcode = SPINOR_OP_READ_1_1_4;
+	return 0;
+}
+
+/*
+ * For both Macronix Dual and Single modes, we don't care about the value of
+ * the Quad Enabled (QE) bit since the memory still replies to Dual or Single
+ * SPI commands.
+ */
+
+static int macronix_set_dual_mode(struct spi_nor *nor)
+{
+	nor->read_proto = SNOR_PROTO_1_1_2;
+	nor->read_opcode = SPINOR_OP_READ_1_1_2;
+	return 0;
+}
+
+static int macronix_set_single_mode(struct spi_nor *nor)
+{
+	nor->read_proto = SNOR_PROTO_1_1_1;
+	return 0;
+}
+
 static int set_quad_mode(struct spi_nor *nor, const struct flash_info *info)
 {
 	int status;
 
 	switch (JEDEC_MFR(info)) {
 	case SNOR_MFR_MACRONIX:
-		status = macronix_quad_enable(nor);
-		if (status) {
-			dev_err(nor->dev, "Macronix quad-read not enabled\n");
-			return -EINVAL;
-		}
-		/* Check whether Macronix QPI mode is enabled. */
-		if (nor->read_proto != SNOR_PROTO_4_4_4)
-			nor->read_proto = SNOR_PROTO_1_1_4;
-		break;
+		return macronix_set_quad_mode(nor);
 
 	case SNOR_MFR_MICRON:
 		/* Check whether Micron Quad mode is enabled. */
@@ -1211,6 +1268,9 @@ static int set_quad_mode(struct spi_nor *nor, const struct flash_info *info)
 static int set_dual_mode(struct spi_nor *nor, const struct flash_info *info)
 {
 	switch (JEDEC_MFR(info)) {
+	case SNOR_MFR_MACRONIX:
+		return macronix_set_dual_mode(nor);
+
 	case SNOR_MFR_MICRON:
 		/* Check whether Micron Dual mode is enabled. */
 		if (nor->read_proto != SNOR_PROTO_2_2_2)
@@ -1229,6 +1289,9 @@ static int set_dual_mode(struct spi_nor *nor, const struct flash_info *info)
 static int set_single_mode(struct spi_nor *nor, const struct flash_info *info)
 {
 	switch (JEDEC_MFR(info)) {
+	case SNOR_MFR_MACRONIX:
+		return macronix_set_single_mode(nor);
+
 	default:
 		nor->read_proto = SNOR_PROTO_1_1_1;
 		break;
-- 
1.8.2.2