Forcing PIO mode instead of DMA via DT property

[Varun Wadekar]

>> One option would be to
>> put a compile time flag in the driver, which prefers PIO than DMA. I
>> believe by default DMA is the first preference.
> Certainly, but please consider you might want to use PIO only on selected
> instances of the driver (aka. selected busses, I wasn't probably clear enough,
> this is a bus driver), not degrade performance on all of them. Possibly due to a
> specific hardware wiring of the particular system.
>

Device Trees are a replacement for board files. If your board uses PIO 
mode due to some hardware limitations, then you need to specify this in 
the .dt for that board. The driver should then just query this property 
and proceed with its init.

Regards,
Varun

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