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

[Vignesh Raghavendra]

On 9/29/20 3:29 PM, Tudor Ambarus wrote:
> 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.
> 

I would make this SPI_NOR_IO_MODE_EN_NON_VOLATILE. Because flashes with
volatile bits to change IO modes are more common than non volatile ones
and above change makes its easier to spot such quirky flashes.

> Signed-off-by: Tudor Ambarus <tudor.ambarus at microchip.com>
> ---
>  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;
>