[MinnowBoard] SPI questions

[John Hawley]

> I saw the thread 'Adding an SPI device to the Minnowboard' from late
> 2013 and 'SPI support on minnowboard v1' from Aug 2014.
> 
> Darren Hart notes:
> Ultimately we want to do things like this without board files by using
> the _DSD mechanisms introduced by the ACPI 5.1 specification last week
> 
> I just wanted to confirm the ACPI mechanism is not the recommended way
> yet, and that using low-speed-spidev.c as a template is still the way to go.

The answer to that will depend on what kernel you are intending to
target.  Kernel's with ACPI 5.1 _DSD support, I think you'd want to push
on that.  Older kernels without that, likely spidev or a more targeted
driver.

> Additional q:
> How do you tell the SPI controller that you have an active-high instead
> of the usual active-low device?  Is it correct to do a bitwise or with
> SPI_CS_HIGH (0x4) with your SPI_MODE in your spi_board_info struct, like:
> .mode = SPI_MODE_0 | SPI_CS_HIGH

That should work, but take my statement with a grain of salt as I
haven't tried it with a device.

- John 'Warthog9' Hawley