dma_alloc_coherent() on PPC32: physical addresses above 2G possible?

Hi all,

I have to implement a workaround for a PCI device which gets into 
trouble if descriptors are located at 32bit addresses, while 31bit 
addresses are fine.  I would like to avoid this workaround on machines 
on which dma_alloc_coherent() won't ever go at memory above 2 GB.

Is defined(CONFIG_PPC32) a safe test for this?  I'm under the impression 
that defined(CONFIG_X86_32) is safe.

Are there any other means to detect when the workaround can be omitted, 
at compile time or at runtime?

PS:  I don't want to set the DMA mask of this device to DMA_31BIT_MASK 
because that would be detrimental to other functions of the device. It's 
a TI TSB43AB22A FireWire controller.
-- 
Stefan Richter
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http://arcgraph.de/sr/