mtd: spi-nor: Introduce SNOR_F_IO_MODE_EN_VOLATILE

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@microchip.com>
Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20201005153138.6437-9-p.yadav@ti.com

drivers/mtd/spi-nor/core.c

@@ -3388,6 +3388,9 @@ 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;

drivers/mtd/spi-nor/core.h

@@ -26,6 +26,7 @@ enum spi_nor_option_flags {
 	SNOR_F_HAS_SR_TB_BIT6	= BIT(11),
 	SNOR_F_HAS_4BIT_BP      = BIT(12),
 	SNOR_F_HAS_SR_BP3_BIT6  = BIT(13),
+	SNOR_F_IO_MODE_EN_VOLATILE = BIT(14),
 };
 
 struct spi_nor_read_command {
@@ -320,6 +321,11 @@ 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;