Re: [PATCH v7 3/7] mtd: spi-nor: core: Allow specifying the byte order in DTR mode

[Michael Walle <mwalle@kernel.org>]

Hi,

> Macronix swaps bytes on a 16-bit boundary when configured in Octal DTR.
> The byte order of 16-bit words is swapped when read or written in 
> 8D-8D-8D
> mode compared to STR modes. Allow operations to specify the byte order 
> in
> DTR mode, so that controllers can swap the bytes back at run-time to
> address the flash's endianness requirements, if they are capable. If 
> the
> controllers are not capable of swapping the bytes, the protocol is
> downgrade via spi_nor_spimem_adjust_hwcaps(). When available, the 
> swapping
> of the bytes is always done regardless if it's a data or register 
> access,
> so that we comply with the JESD216 requirements: "Byte order of 16-bit
> words is swapped when read in 8D-8D-8D mode compared to 1-1-1".
> 
> Merge Tudor's patch and add modifications for suiting newer version
> of Linux kernel.
> 
> Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
> Signed-off-by: JaimeLiao <jaimeliao@mxic.com.tw>
> ---
>  drivers/mtd/spi-nor/core.c | 8 ++++++++
>  drivers/mtd/spi-nor/core.h | 1 +
>  2 files changed, 9 insertions(+)
> 
> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
> index 1c443fe568cf..f659dd037a25 100644
> --- a/drivers/mtd/spi-nor/core.c
> +++ b/drivers/mtd/spi-nor/core.c
> @@ -70,6 +70,13 @@ static u8 spi_nor_get_cmd_ext(const struct spi_nor 
> *nor,
>  	}
>  }
> 
> +static inline bool spi_nor_is_octal_dtr_swab16(const struct spi_nor 
> *nor,
> +						enum spi_nor_protocol proto)
> +{
> +	return (proto == SNOR_PROTO_8_8_8_DTR) &&
> +		(nor->flags & SNOR_F_DTR_SWAB16);
> +}
> +
>  /**
>   * spi_nor_spimem_setup_op() - Set up common properties of a spi-mem 
> op.
>   * @nor:		pointer to a 'struct spi_nor'
> @@ -105,6 +112,7 @@ void spi_nor_spimem_setup_op(const struct spi_nor 
> *nor,
>  		op->addr.dtr = true;
>  		op->dummy.dtr = true;
>  		op->data.dtr = true;
> +		op->data.dtr_swab16 = spi_nor_is_octal_dtr_swab16(nor, proto);

Just use
   dtr_swap16 = nor->flags & SNOR_F_DTR_SWAP16;

Again, I don't really like DTR_SWAP16. JESD216 just mention swapping for
8d8d8d. Depends on how generic we want to go. I'd go with swap16 and 
mention
that for now, it is only applicable if data.buswidth == 8 and
data.dtr == true.

-michael

>  		/* 2 bytes per clock cycle in DTR mode. */
>  		op->dummy.nbytes *= 2;
> diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
> index 93cd2fc3606d..fe1259b32110 100644
> --- a/drivers/mtd/spi-nor/core.h
> +++ b/drivers/mtd/spi-nor/core.h
> @@ -140,6 +140,7 @@ enum spi_nor_option_flags {
>  	SNOR_F_RWW		= BIT(14),
>  	SNOR_F_ECC		= BIT(15),
>  	SNOR_F_NO_WP		= BIT(16),
> +	SNOR_F_DTR_SWAB16       = BIT(17),
>  };
> 
>  struct spi_nor_read_command {

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