Forcing PIO mode instead of DMA via DT property

[Aggrwal Poonam-B10812]

> -----Original Message-----
> From: devicetree-discuss [mailto:devicetree-discuss-
> bounces+poonam.aggrwal=freescale.com at lists.ozlabs.org] On Behalf Of Marek
> Vasut
> Sent: Monday, July 23, 2012 2:58 AM
> To: devicetree-discuss at lists.ozlabs.org
> Cc: pavel at denx.de; Wolfgang Denk
> Subject: Forcing PIO mode instead of DMA via DT property
> 
> Hi guys,
> 
> I'm trying to implement a driver that can do both DMA and PIO, and it
> would be nice if the user was able to select the mode (on a per-bus
> basis) using the DT.
> The PIO mode can reduce the overhead in some cases and therefore be
> better choice than the DMA (for example when most transfers move only
> very few data, or when board-specific hardware properties kick in).
> 
> I was thinking about using some "manf,use-pio" DT property, but I haven't
> found any such example yet, so I wonder if this is a good idea.
Not sure, but as far as I understand device tree is to publish the hardware capabilities, not the user choice/configuration.
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.

Regards
Poonam
> 
> What is your suggestion how I shoud address such a problem?
> 
> Thanks in advance!
> 
> Best regards,
> Marek Vasut
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