[PATCH v6 5/7] spi: mxic: Add support for swapping byte

[Michael Walle]

Hi Jaime,

>> > Some SPI-NOR flash swap the bytes on a 16-bit boundary when
>> > configured in Octal DTR mode. It means data format D0 D1 D2 D3
>> > would be swapped to D1 D0 D3 D2. So that whether controller
>> > support swapping bytes should be checked before enable Octal
>> > DTR mode. Add swap byte support on a 16-bit boundary when
>> > configured in Octal DTR mode for Macronix xSPI host controller
>> > dirver.
>> >
>> > Signed-off-by: JaimeLiao <jaimeliao at mxic.com.tw>
>> > ---
>> >  drivers/spi/spi-mxic.c | 1 +
>> >  1 file changed, 1 insertion(+)
>> >
>> > diff --git a/drivers/spi/spi-mxic.c b/drivers/spi/spi-mxic.c
>> > index 60c9f3048ac9..085c9037d6f5 100644
>> > --- a/drivers/spi/spi-mxic.c
>> > +++ b/drivers/spi/spi-mxic.c
>> > @@ -572,6 +572,7 @@ static const struct spi_controller_mem_ops
>> > mxic_spi_mem_ops = {
>> >
>> >  static const struct spi_controller_mem_caps mxic_spi_mem_caps = {
>> >       .dtr = true,
>> > +     .dtr_swab16 = true,
>> >       .ecc = true,
>> >  };
>> 
>> I'm confused. How can this swap the bytes depending on the flashes
>> requirements? I.e. the controller should look at the spi-mem operation
>> and either swap the bytes or it should leave them as is.
> Byte order in 8D-8D-8D mode could get by parsing BFPT 18th Dword 31th 
> bit.
> I think flash driver should notify controller driver and verify whether 
> the
> controller driver support byte swap functionality. If flash requires 
> byte swap
> in octal DTR mode but the controller driver doesn't support it, then 
> octal DTR
> should not be enabled.

Correct. But the above means, the controller *supports* swapping the 
bytes
if the flash requires it. But where is the code in the spi-mxic driver 
which
actually controls the swapping depending on the dtr_swab16 property in
spi_mem_op?

> The controller driver should indicate in the
> description of
> "spi_controller_mem_caps" whether this feature is supported. The 
> implementation
> of this feature should be handled separately by each controller drive
> since the design
> may vary for each one.

Correct. And because your flashes apparently need that swapping, the 
driver
will have to have support for that.

-michael