[RFC PATCH 1/3] mtd: spi-nor: Introduce SNOR_F_IO_MODE_EN_VOLATILE

[Tudor Ambarus]

We don't want to enter a stateful mode, where a X-X-X I/O mode
is entered by setting a non-volatile bit, because in case of a
reset or a crash, once in the non-volatile mode, we may not be able
to recover in bootloaders and we may break the SPI NOR boot.

Forbid by default the I/O modes that are set via a non-volatile bit.

SPI_NOR_IO_MODE_EN_VOLATILE should be set just for the flashes that
don't define the optional SFDP SCCR Map, so that we don't pollute the
flash info flags.

Signed-off-by: Tudor Ambarus <tudor.ambarus@xxxxxxxxxxxxx>
---
 drivers/mtd/spi-nor/core.c | 6 ++++++
 drivers/mtd/spi-nor/core.h | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
index 34edfcf33172..c149b318e2e8 100644
--- a/drivers/mtd/spi-nor/core.c
+++ b/drivers/mtd/spi-nor/core.c
@@ -3089,6 +3089,9 @@ static int spi_nor_octal_dtr_enable(struct spi_nor *nor, bool enable)
 	      nor->write_proto == SNOR_PROTO_8_8_8_DTR))
 		return 0;
 
+	if (!(nor->flags & SNOR_F_IO_MODE_EN_VOLATILE))
+		return 0;
+
 	ret = nor->params->octal_dtr_enable(nor, enable);
 	if (ret)
 		return ret;
@@ -3474,6 +3477,9 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
 	if (info->flags & SPI_NOR_4B_OPCODES)
 		nor->flags |= SNOR_F_4B_OPCODES;
 
+	if (info->flags & SPI_NOR_IO_MODE_EN_VOLATILE)
+		nor->flags |= SNOR_F_IO_MODE_EN_VOLATILE;
+
 	ret = spi_nor_set_addr_width(nor);
 	if (ret)
 		return ret;
diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
index 10dc03506f93..c2755c82f978 100644
--- a/drivers/mtd/spi-nor/core.h
+++ b/drivers/mtd/spi-nor/core.h
@@ -27,6 +27,7 @@ enum spi_nor_option_flags {
 	SNOR_F_HAS_4BIT_BP      = BIT(12),
 	SNOR_F_HAS_SR_BP3_BIT6  = BIT(13),
 	SNOR_F_SOFT_RESET	= BIT(14),
+	SNOR_F_IO_MODE_EN_VOLATILE = BIT(15),
 };
 
 struct spi_nor_read_command {
@@ -323,6 +324,11 @@ struct flash_info {
 					 */
 #define SPI_NOR_OCTAL_DTR_READ	BIT(19) /* Flash supports octal DTR Read. */
 #define SPI_NOR_OCTAL_DTR_PP	BIT(20) /* Flash supports Octal DTR Page Program */
+#define SPI_NOR_IO_MODE_EN_VOLATILE	BIT(21) /*
+						 * Flash enables the best
+						 * available I/O mode via a
+						 * volatile bit.
+						 */
 
 	/* Part specific fixup hooks. */
 	const struct spi_nor_fixups *fixups;
-- 
2.25.1