Maximum ioremap size for ppc arch?

[michael.firth at bt.com]

I'm trying to get am MPC834x system running that has 256MBytes of NOR
flash connected.

The physmap flash driver is failing to ioremap() that amount of space,
while on a similar system with 128Mbytes of flash, there are no
problems.

Is this a known limitation of ioremap() on the ppc architecture, or
specifically the MPC834x family, and is there any (hopefully easy) way
to increase this limit?

Thanks

Michael