mtd: spi-nor: Add quad I/O support for Micron SPI NOR

This patch adds code which enables Quad I/O mode on Micron SPI NOR flashes.

For Micron SPI NOR flash, enabling or disabling quad I/O protocol can be
done By two methods, which are to use EVCR (Enhanced Volatile
Configuration Register) and the ENTER QUAD I/O MODE command. There is no
difference between these two methods. Unfortunately, for some Micron SPI
NOR flashes, there no ENTER Quad I/O command (35h), such as n25q064. But
for all current Micron SPI NOR, if it support quad I/O mode, using EVCR
definitely be supported. It is a recommended method to enable Quad I/O
mode by EVCR, Quad I/O protocol bit 7. When EVCR bit 7 is reset to 0,
the SPI NOR flash will operate in quad I/O mode.

This patch has been tested on N25Q512A and MT25TL256BAA1ESF. Micron SPI
NOR of spi_nor_ids[] table all support this method.
Signed-off-by: Bean Huo <beanhuo@micron.com>
Acked-by: Marek Vasut <marex@denx.de>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/spi-nor/spi-nor.c

@@ -560,14 +560,14 @@ static const struct spi_device_id spi_nor_ids[] = {
 	{ "mx66l1g55g",  INFO(0xc2261b, 0, 64 * 1024, 2048, SPI_NOR_QUAD_READ) },
 
 	/* Micron */
-	{ "n25q032",	 INFO(0x20ba16, 0, 64 * 1024,   64, 0) },
-	{ "n25q064",     INFO(0x20ba17, 0, 64 * 1024,  128, 0) },
-	{ "n25q128a11",  INFO(0x20bb18, 0, 64 * 1024,  256, 0) },
-	{ "n25q128a13",  INFO(0x20ba18, 0, 64 * 1024,  256, 0) },
-	{ "n25q256a",    INFO(0x20ba19, 0, 64 * 1024,  512, SECT_4K) },
-	{ "n25q512a",    INFO(0x20bb20, 0, 64 * 1024, 1024, SECT_4K) },
-	{ "n25q512ax3",  INFO(0x20ba20, 0, 64 * 1024, 1024, USE_FSR) },
-	{ "n25q00",      INFO(0x20ba21, 0, 64 * 1024, 2048, USE_FSR) },
+	{ "n25q032",	 INFO(0x20ba16, 0, 64 * 1024,   64, SPI_NOR_QUAD_READ) },
+	{ "n25q064",     INFO(0x20ba17, 0, 64 * 1024,  128, SPI_NOR_QUAD_READ) },
+	{ "n25q128a11",  INFO(0x20bb18, 0, 64 * 1024,  256, SPI_NOR_QUAD_READ) },
+	{ "n25q128a13",  INFO(0x20ba18, 0, 64 * 1024,  256, SPI_NOR_QUAD_READ) },
+	{ "n25q256a",    INFO(0x20ba19, 0, 64 * 1024,  512, SECT_4K | SPI_NOR_QUAD_READ) },
+	{ "n25q512a",    INFO(0x20bb20, 0, 64 * 1024, 1024, SECT_4K | USE_FSR | SPI_NOR_QUAD_READ) },
+	{ "n25q512ax3",  INFO(0x20ba20, 0, 64 * 1024, 1024, SECT_4K | USE_FSR | SPI_NOR_QUAD_READ) },
+	{ "n25q00",      INFO(0x20ba21, 0, 64 * 1024, 2048, SECT_4K | USE_FSR | SPI_NOR_QUAD_READ) },
 
 	/* PMC */
 	{ "pm25lv512",   INFO(0,        0, 32 * 1024,    2, SECT_4K_PMC) },
@@ -891,6 +891,45 @@ static int spansion_quad_enable(struct spi_nor *nor)
 	return 0;
 }
 
+static int micron_quad_enable(struct spi_nor *nor)
+{
+	int ret;
+	u8 val;
+
+	ret = nor->read_reg(nor, SPINOR_OP_RD_EVCR, &val, 1);
+	if (ret < 0) {
+		dev_err(nor->dev, "error %d reading EVCR\n", ret);
+		return ret;
+	}
+
+	write_enable(nor);
+
+	/* set EVCR, enable quad I/O */
+	nor->cmd_buf[0] = val & ~EVCR_QUAD_EN_MICRON;
+	ret = nor->write_reg(nor, SPINOR_OP_WD_EVCR, nor->cmd_buf, 1, 0);
+	if (ret < 0) {
+		dev_err(nor->dev, "error while writing EVCR register\n");
+		return ret;
+	}
+
+	ret = spi_nor_wait_till_ready(nor);
+	if (ret)
+		return ret;
+
+	/* read EVCR and check it */
+	ret = nor->read_reg(nor, SPINOR_OP_RD_EVCR, &val, 1);
+	if (ret < 0) {
+		dev_err(nor->dev, "error %d reading EVCR\n", ret);
+		return ret;
+	}
+	if (val & EVCR_QUAD_EN_MICRON) {
+		dev_err(nor->dev, "Micron EVCR Quad bit not clear\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int set_quad_mode(struct spi_nor *nor, struct flash_info *info)
 {
 	int status;
@@ -903,6 +942,13 @@ static int set_quad_mode(struct spi_nor *nor, struct flash_info *info)
 			return -EINVAL;
 		}
 		return status;
+	case CFI_MFR_ST:
+		status = micron_quad_enable(nor);
+		if (status) {
+			dev_err(nor->dev, "Micron quad-read not enabled\n");
+			return -EINVAL;
+		}
+		return status;
 	default:
 		status = spansion_quad_enable(nor);
 		if (status) {

include/linux/mtd/spi-nor.h

@@ -56,6 +56,10 @@
 /* Used for Spansion flashes only. */
 #define SPINOR_OP_BRWR		0x17	/* Bank register write */
 
+/* Used for Micron flashes only. */
+#define SPINOR_OP_RD_EVCR      0x65    /* Read EVCR register */
+#define SPINOR_OP_WD_EVCR      0x61    /* Write EVCR register */
+
 /* Status Register bits. */
 #define SR_WIP			1	/* Write in progress */
 #define SR_WEL			2	/* Write enable latch */
@@ -67,6 +71,9 @@
 
 #define SR_QUAD_EN_MX		0x40	/* Macronix Quad I/O */
 
+/* Enhanced Volatile Configuration Register bits */
+#define EVCR_QUAD_EN_MICRON    0x80    /* Micron Quad I/O */
+
 /* Flag Status Register bits */
 #define FSR_READY		0x80