[PATCH v3 11/14] mtd: spi-nor: configure the number of dummy clock cycles on Spansion memories

[Cyrille Pitchen]

On Spansion memories, the number of dummy clock cycles to be used during
Fast Read commands is configured through the 2bit latency code (LC). These
bits are non-volatile inside the Configuration Register.

To avoid breaking the configuration expected at reset by some bootloaders,
we'd rather read the latency code and set the nor->read_dummy value
accordingly than update those non-volatile bits.

Since the Quad Enable non-volatile bit can be read at the same time from
the Control Register, we now check its value to avoid some calls of the
spansion_quad_enable() function when they are not needed.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@xxxxxxxxx>
---
 drivers/mtd/spi-nor/spi-nor.c | 159 ++++++++++++++++++++++++++++++++++++------
 1 file changed, 137 insertions(+), 22 deletions(-)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index c560fbbb8479..356db141dcb2 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -1668,47 +1668,162 @@ static int micron_set_single_mode(struct spi_nor *nor)
 	return micron_set_dummy_cycles(nor, read_dummy);
 }
 
-static int spansion_set_quad_mode(struct spi_nor *nor)
+static inline int spansion_get_config(struct spi_nor *nor,
+				      bool *quad_enabled,
+				      u8 *latency_code)
 {
-	int status;
+	int cr;
 
-	status = spansion_quad_enable(nor);
-	if (status) {
-		dev_err(nor->dev, "Spansion quad-read not enabled\n");
+	cr = read_cr(nor);
+	if (cr < 0) {
+		dev_err(nor->dev,
+			"error while reading the configuration register\n");
+		return cr;
+	}
+
+	if (quad_enabled)
+		*quad_enabled = !!(cr & CR_QUAD_EN_SPAN);
+
+	if (latency_code)
+		*latency_code = (u8)((cr & GENMASK(7, 6)) >> 6);
+
+	return 0;
+}
+
+static int spansion_set_dummy_cycles(struct spi_nor *nor, u8 latency_code)
+{
+	/* SDR dummy cycles */
+	switch (nor->read_opcode) {
+	case SPINOR_OP_READ:
+	case SPINOR_OP_READ4:
+		nor->read_dummy = 0;
+		break;
+
+	case SPINOR_OP_READ_FAST:
+	case SPINOR_OP_READ_1_1_2:
+	case SPINOR_OP_READ_1_1_4:
+	case SPINOR_OP_READ4_FAST:
+	case SPINOR_OP_READ4_1_1_2:
+	case SPINOR_OP_READ4_1_1_4:
+		nor->read_dummy = (latency_code == 3) ? 0 : 8;
+		break;
+
+	case SPINOR_OP_READ_1_2_2:
+	case SPINOR_OP_READ4_1_2_2:
+		switch (latency_code) {
+		default:
+		case 0:
+		case 3:
+			nor->read_dummy = 4;
+			break;
+		case 1:
+			nor->read_dummy = 5;
+			break;
+		case 2:
+			nor->read_dummy = 6;
+			break;
+		}
+		break;
+
+
+	case SPINOR_OP_READ_1_4_4:
+	case SPINOR_OP_READ4_1_4_4:
+		switch (latency_code) {
+		default:
+		case 0:
+		case 1:
+			nor->read_dummy = 4;
+			break;
+		case 2:
+			nor->read_dummy = 5;
+			break;
+		case 3:
+			nor->read_dummy = 1;
+			break;
+		}
+
+	default:
 		return -EINVAL;
 	}
+
+	return 0;
+}
+
+static int spansion_set_quad_mode(struct spi_nor *nor)
+{
+	bool quad_enabled;
+	u8 latency_code;
+	int ret;
+
+	/*
+	 * The QUAD bit of Configuration Register must be set (CR Bit1=1) for
+	 * using any Quad SPI command.
+	 */
+	ret = spansion_get_config(nor, &quad_enabled, &latency_code);
+	if (ret)
+		return ret;
+
+	/* The Quad mode should be enabled ... */
+	if (!quad_enabled) {
+		/* ... if not try to enable it. */
+		dev_warn(nor->dev, "Spansion Quad mode disabled, enable it\n");
+		ret = spansion_quad_enable(nor);
+		if (ret)
+			return ret;
+	}
+
+	/*
+	 * Don't use the Fast Read Quad I/O (0xeb / 0xec) commands as their
+	 * number of dummy cycles can not be set to a multiple of 8: some SPI
+	 * controllers, especially those relying on the m25p80 driver, expect
+	 * the number of dummy cycles to be a multiple of 8.
+	 * Also when using a Fast Read Quad I/O command, the memory checks the
+	 * value of the first mode/dummy cycles to decice whether it enters or
+	 * leaves the Countinuous Read mode. We should never enter the
+	 * Countinuous Read mode as the spi-nor framework doesn't support it.
+	 * For all these reason, we'd rather use the Fast Read Quad Output
+	 * 1-1-4 (0x6b / 0x6c) commands instead.
+	 */
 	nor->read_proto = SNOR_PROTO_1_1_4;
 	nor->read_opcode = SPINOR_OP_READ_1_1_4;
-	nor->read_dummy = 8;
-	return 0;
+	return spansion_set_dummy_cycles(nor, latency_code);
 }
 
 static int spansion_set_dual_mode(struct spi_nor *nor)
 {
+	u8 latency_code;
+	int ret;
+
+	/* We don't care about the quad mode status */
+	ret = spansion_get_config(nor, NULL, &latency_code);
+	if (ret)
+		return ret;
+
+	/*
+	 * Don't use the Fast Read Dual I/O (0xbb / 0xbc) commands as their
+	 * number of dummy cycles can not bet set to a multiple of 8: some SPI
+	 * controllers, especially those relying on the m25p80 driver, expect
+	 * the number of dummy cycles to be a multiple of 8.
+	 * For this reason, w'd rather use the Fast Read Dual Output 1-1-2
+	 * (0x3b / 0x3c) commands instead.
+	 */
 	nor->read_proto = SNOR_PROTO_1_1_2;
 	nor->read_opcode = SPINOR_OP_READ_1_1_2;
-	nor->read_dummy = 8;
-	return 0;
+	return spansion_set_dummy_cycles(nor, latency_code);
 }
 
 static int spansion_set_single_mode(struct spi_nor *nor)
 {
-	u8 read_dummy;
-
-	switch (nor->read_opcode) {
-	case SPINOR_OP_READ:
-	case SPINOR_OP_READ4:
-		read_dummy = 0;
-		break;
+	u8 latency_code;
+	int ret;
 
-	default:
-		read_dummy = 8;
-		break;
-	}
+	/* We don't care about the quad mode status */
+	ret = spansion_get_config(nor, NULL, &latency_code);
+	if (ret)
+		return ret;
 
 	nor->read_proto = SNOR_PROTO_1_1_1;
-	nor->read_dummy = read_dummy;
-	return 0;
+	return spansion_set_dummy_cycles(nor, latency_code);
 }
 
 static int set_quad_mode(struct spi_nor *nor, const struct flash_info *info)
-- 
1.8.2.2