mtd: spi-nor-core: Perform a Soft Reset on shutdown

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.

Since spi-nor-tiny doesn't (and likely shouldn't) have
spi_nor_soft_reset(), add a dummy spi_nor_remove() for it that does
nothing.

Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>

drivers/mtd/spi/Kconfig

@@ -97,6 +97,13 @@ config SPI_FLASH_SMART_HWCAPS
 	 can support a type of operation in a much more refined way compared
 	 to using flags like SPI_RX_DUAL, SPI_TX_QUAD, etc.
 
+config SPI_FLASH_SOFT_RESET
+	bool "Software Reset support for SPI NOR flashes"
+	default n
+	help
+	 Enable support for xSPI Software Reset. It will be used to switch from
+	 Octal DTR mode to legacy mode on shutdown and boot (if enabled).
+
 config SPI_FLASH_BAR
 	bool "SPI flash Bank/Extended address register support"
 	help

drivers/mtd/spi/sf_probe.c

@@ -151,6 +151,11 @@ int spi_flash_std_probe(struct udevice *dev)
 static int spi_flash_std_remove(struct udevice *dev)
 {
 	struct spi_flash *flash = dev_get_uclass_priv(dev);
+	int ret;
+
+	ret = spi_nor_remove(flash);
+	if (ret)
+		return ret;
 
 	if (CONFIG_IS_ENABLED(SPI_FLASH_MTD))
 		spi_flash_mtd_unregister(flash);
@@ -178,6 +183,7 @@ U_BOOT_DRIVER(jedec_spi_nor) = {
 	.remove		= spi_flash_std_remove,
 	.priv_auto	= sizeof(struct spi_nor),
 	.ops		= &spi_flash_std_ops,
+	.flags		= DM_FLAG_OS_PREPARE,
 };
 
 DM_DRIVER_ALIAS(jedec_spi_nor, spansion_m25p16)

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

@@ -22,6 +22,7 @@
 #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>
@@ -200,6 +201,8 @@ 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.
@@ -2971,6 +2974,71 @@ static int spi_nor_init(struct spi_nor *nor)
 	return 0;
 }
 
+#ifdef CONFIG_SPI_FLASH_SOFT_RESET
+/**
+ * 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, 0),
+			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, 0),
+			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;
+}
+#endif /* CONFIG_SPI_FLASH_SOFT_RESET */
+
+int spi_nor_remove(struct spi_nor *nor)
+{
+#ifdef CONFIG_SPI_FLASH_SOFT_RESET
+	if (nor->info->flags & SPI_NOR_OCTAL_DTR_READ &&
+	    nor->flags & SNOR_F_SOFT_RESET)
+		return spi_nor_soft_reset(nor);
+#endif
+
+	return 0;
+}
+
 void spi_nor_set_fixups(struct spi_nor *nor)
 {
 }

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) */
@@ -562,4 +564,19 @@ device_node *spi_nor_get_flash_node(struct spi_nor *nor)
  */
 int spi_nor_scan(struct spi_nor *nor);
 
+#if CONFIG_IS_ENABLED(SPI_FLASH_TINY)
+static inline int spi_nor_remove(struct spi_nor *nor)
+{
+	return 0;
+}
+#else
+/**
+ * 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
+
 #endif