[PATCH v4 17/20] mtd: spi-nor-core: Perform a Soft Reset on shutdown

[Pratyush Yadav]

On probe, the SPI NOR core will put a flash in 8D-8D-8D mode if it
supports it. But Linux as of now expects to get the flash in 1S-1S-1S
mode. Handing the flash to Linux in Octal DTR mode means the kernel will
fail to detect the flash.

So, we need to reset to Power-on-Reset (POR) state before handing off
the flash. A Software Reset command can be used to do this.

One limitation of the soft reset is that it will restore state from
non-volatile registers in some flashes. This means that if the flash was
set to 8D mode in a non-volatile configuration, a soft reset won't help.
This commit assumes that we don't set any non-volatile bits anywhere,
and the flash doesn't have any non-volatile Octal DTR mode
configuration.

Signed-off-by: Pratyush Yadav <p.yadav at ti.com>
---
 drivers/mtd/spi/sf_probe.c     |  9 +++++
 drivers/mtd/spi/spi-nor-core.c | 64 ++++++++++++++++++++++++++++++++++
 include/linux/mtd/spi-nor.h    | 10 ++++++
 3 files changed, 83 insertions(+)

diff --git a/drivers/mtd/spi/sf_probe.c b/drivers/mtd/spi/sf_probe.c
index c2e51f9c68..fc658418e0 100644
--- a/drivers/mtd/spi/sf_probe.c
+++ b/drivers/mtd/spi/sf_probe.c
@@ -153,6 +153,14 @@ int spi_flash_std_probe(struct udevice *dev)
 
 static int spi_flash_std_remove(struct udevice *dev)
 {
+	struct spi_flash *flash;
+	int ret;
+
+	flash = dev_get_uclass_priv(dev);
+	ret = spi_nor_remove(flash);
+	if (ret)
+		return ret;
+
 #if CONFIG_IS_ENABLED(SPI_FLASH_MTD)
 	spi_flash_mtd_unregister();
 #endif
@@ -179,6 +187,7 @@ U_BOOT_DRIVER(spi_flash_std) = {
 	.remove		= spi_flash_std_remove,
 	.priv_auto_alloc_size = sizeof(struct spi_flash),
 	.ops		= &spi_flash_std_ops,
+	.flags		= DM_FLAG_OS_PREPARE,
 };
 
 #endif /* CONFIG_DM_SPI_FLASH */
diff --git a/drivers/mtd/spi/spi-nor-core.c b/drivers/mtd/spi/spi-nor-core.c
index 03bf34a3c9..ca445d7278 100644
--- a/drivers/mtd/spi/spi-nor-core.c
+++ b/drivers/mtd/spi/spi-nor-core.c
@@ -20,6 +20,7 @@
 #include <linux/math64.h>
 #include <linux/sizes.h>
 #include <linux/bitfield.h>
+#include <linux/delay.h>
 
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/spi-nor.h>
@@ -198,6 +199,8 @@ struct spi_nor_fixups {
 			  struct spi_nor_flash_parameter *params);
 };
 
+#define SPI_NOR_SRST_SLEEP_LEN			200
+
 /**
  * spi_nor_get_cmd_ext() - Get the command opcode extension based on the
  *			   extension type.
@@ -2883,6 +2886,67 @@ static int spi_nor_init(struct spi_nor *nor)
 	return 0;
 }
 
+/**
+ * spi_nor_soft_reset() - perform the JEDEC Software Reset sequence
+ * @nor:	the spi_nor structure
+ *
+ * This function can be used to switch from Octal DTR mode to legacy mode on a
+ * flash that supports it. The soft reset is executed in Octal DTR mode.
+ *
+ * Return: 0 for success, -errno for failure.
+ */
+static int spi_nor_soft_reset(struct spi_nor *nor)
+{
+	struct spi_mem_op op;
+	int ret;
+	enum spi_nor_cmd_ext ext;
+
+	ext = nor->cmd_ext_type;
+	nor->cmd_ext_type = SPI_NOR_EXT_REPEAT;
+
+	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);
+	spi_nor_setup_op(nor, &op, SNOR_PROTO_8_8_8_DTR);
+	ret = spi_mem_exec_op(nor->spi, &op);
+	if (ret) {
+		dev_warn(nor->dev, "Software reset enable failed: %d\n", ret);
+		goto out;
+	}
+
+	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);
+	spi_nor_setup_op(nor, &op, SNOR_PROTO_8_8_8_DTR);
+	ret = spi_mem_exec_op(nor->spi, &op);
+	if (ret) {
+		dev_warn(nor->dev, "Software reset failed: %d\n", ret);
+		goto out;
+	}
+
+	/*
+	 * 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, wait for 200ms just to be sure.
+	 */
+	udelay(SPI_NOR_SRST_SLEEP_LEN);
+
+out:
+	nor->cmd_ext_type = ext;
+	return ret;
+}
+
+int spi_nor_remove(struct spi_nor *nor)
+{
+	if (nor->info->flags & SPI_NOR_OCTAL_DTR_READ &&
+	    nor->flags & SNOR_F_SOFT_RESET)
+		return spi_nor_soft_reset(nor);
+
+	return 0;
+}
+
 int spi_nor_scan(struct spi_nor *nor)
 {
 	struct spi_nor_flash_parameter params;
diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
index 0850f1d775..d8cebf1dcf 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) */
@@ -557,4 +559,12 @@ device_node *spi_nor_get_flash_node(struct spi_nor *nor)
  */
 int spi_nor_scan(struct spi_nor *nor);
 
+/**
+ * spi_nor_remove() - perform cleanup before booting to the next stage
+ * @nor:	the spi_nor structure
+ *
+ * Return: 0 for success, -errno for failure.
+ */
+int spi_nor_remove(struct spi_nor *nor);
+
 #endif
-- 
2.26.2