[PATCH v3 10/12] mtd: spi-nor: perform a Soft Reset on shutdown

[Pratyush Yadav <p.yadav@xxxxxx>]

A Software Reset sequence will return the flash to Power-on-Reset (POR)
state. It consists of two commands: Soft Reset Enable and Soft Reset.

Perform a Soft Reset on shutdown on flashes that support it so that the
flash can be reset to its initial state and any configurations made by
spi-nor (given that they're only done in volatile registers) will be
reset. This will hand back the flash in pristine state for any further
operations on it.

Signed-off-by: Pratyush Yadav <p.yadav@xxxxxx>
---
 drivers/mtd/spi-nor/spi-nor.c | 50 +++++++++++++++++++++++++++++++++++
 include/linux/mtd/spi-nor.h   |  3 +++
 2 files changed, 53 insertions(+)

diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index 5e225d1b29f7..fcc087ff5148 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -253,6 +253,7 @@ struct flash_info {
 					 * SPI_NOR_HAS_TB.
 					 */
 #define SPI_NOR_OCTAL_DTR_READ	BIT(18)	/* Flash supports octal DTR Read. */
+#define SPI_NOR_SOFT_RESET	BIT(19) /* Flash supports soft reset command */
 
 	/* Part specific fixup hooks. */
 	const struct spi_nor_fixups *fixups;
@@ -260,6 +261,9 @@ struct flash_info {
 
 #define JEDEC_MFR(info)	((info)->id[0])
 
+#define SPI_NOR_SRST_SLEEP_MIN	200
+#define SPI_NOR_SRST_SLEEP_MAX	400
+
 /**
  * spi_nor_get_cmd_ext() - Get the command opcode extension based on the
  *			   extension type.
@@ -5336,6 +5340,45 @@ static int spi_nor_init(struct spi_nor *nor)
 	return 0;
 }
 
+static void spi_nor_soft_reset(struct spi_nor *nor)
+{
+	struct spi_mem_op op;
+	int ret;
+
+	op = (struct spi_mem_op)SPI_MEM_OP(SPI_MEM_OP_CMD(SPINOR_OP_SRSTEN, 8),
+			SPI_MEM_OP_NO_DUMMY,
+			SPI_MEM_OP_NO_ADDR,
+			SPI_MEM_OP_NO_DATA);
+	op.cmd.dtr = op.addr.dtr = op.dummy.dtr = op.data.dtr = true;
+	op.cmd.opcode <<= 8;
+	op.cmd.opcode |= spi_nor_get_cmd_ext(nor, &op);
+	ret = spi_mem_exec_op(nor->spimem, &op);
+	if (ret) {
+		dev_warn(nor->dev, "Software reset failed: %d\n", ret);
+		return;
+	}
+
+	op = (struct spi_mem_op)SPI_MEM_OP(SPI_MEM_OP_CMD(SPINOR_OP_SRST, 8),
+			SPI_MEM_OP_NO_DUMMY,
+			SPI_MEM_OP_NO_ADDR,
+			SPI_MEM_OP_NO_DATA);
+	op.cmd.dtr = op.addr.dtr = op.dummy.dtr = op.data.dtr = true;
+	op.cmd.opcode <<= 8;
+	op.cmd.opcode |= spi_nor_get_cmd_ext(nor, &op);
+	ret = spi_mem_exec_op(nor->spimem, &op);
+	if (ret) {
+		dev_warn(nor->dev, "Software reset failed: %d\n", ret);
+		return;
+	}
+
+	/*
+	 * Software Reset is not instant, and the delay varies from flash to
+	 * flash. Looking at a few flashes, most range somewhere below 100
+	 * microseconds. So, sleep for a range of 200-400 us.
+	 */
+	usleep_range(SPI_NOR_SRST_SLEEP_MIN, SPI_NOR_SRST_SLEEP_MAX);
+}
+
 /* mtd resume handler */
 static void spi_nor_resume(struct mtd_info *mtd)
 {
@@ -5355,6 +5398,10 @@ void spi_nor_restore(struct spi_nor *nor)
 	if (nor->addr_width == 4 && !(nor->flags & SNOR_F_4B_OPCODES) &&
 	    nor->flags & SNOR_F_BROKEN_RESET)
 		nor->params.set_4byte(nor, false);
+
+	if (nor->info->flags & SPI_NOR_OCTAL_DTR_READ &&
+	    nor->flags & SNOR_F_SOFT_RESET)
+		spi_nor_soft_reset(nor);
 }
 EXPORT_SYMBOL_GPL(spi_nor_restore);
 
@@ -5539,6 +5586,9 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
 			nor->flags |= SNOR_F_HAS_SR_TB_BIT6;
 	}
 
+	if (info->flags & SPI_NOR_SOFT_RESET)
+		nor->flags |= SNOR_F_SOFT_RESET;
+
 	if (info->flags & NO_CHIP_ERASE)
 		nor->flags |= SNOR_F_NO_OP_CHIP_ERASE;
 	if (info->flags & USE_CLSR)
diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
index 923bd34ced84..13679197dec1 100644
--- a/include/linux/mtd/spi-nor.h
+++ b/include/linux/mtd/spi-nor.h
@@ -67,6 +67,8 @@
 #define SPINOR_OP_CLFSR		0x50	/* Clear flag status register */
 #define SPINOR_OP_RDEAR		0xc8	/* Read Extended Address Register */
 #define SPINOR_OP_WREAR		0xc5	/* Write Extended Address Register */
+#define SPINOR_OP_SRSTEN	0x66	/* Software Reset Enable */
+#define SPINOR_OP_SRST		0x99	/* Software Reset */
 
 /* 4-byte address opcodes - used on Spansion and some Macronix flashes. */
 #define SPINOR_OP_READ_4B	0x13	/* Read data bytes (low frequency) */
@@ -241,6 +243,7 @@ enum spi_nor_option_flags {
 	SNOR_F_HAS_16BIT_SR	= BIT(9),
 	SNOR_F_NO_READ_CR	= BIT(10),
 	SNOR_F_HAS_SR_TB_BIT6	= BIT(11),
+	SNOR_F_SOFT_RESET	= BIT(12),
 
 };
 
-- 
2.25.0