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

[liao jaime]

Hi Michael


>
> 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 at linaro.org>
> > Signed-off-by: JaimeLiao <jaimeliao at 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;
Got it.

>
> 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 {

Thanks
Jaime