Andrew Gallatin wrote:
> Me too.  I was about to just change it for alpha, but then I wondered
> if there was a reason for having BUS_SPACE_MAXSIZE < MAXPHYS.

>From what I understand, the Alpha is limited to doing transfers
in the first 2G of memory.  I'm not sure if the ISA 16M memory
limit is in there anywhere, either.

The problem is that a DMA initiated by a bus mastering device
can only access as many bis of address space as are passed
through the bus, end-to-end.

For ISA, this ends up being a 16M limit; I think the 2G limit
on Alpha is because the limit is 32 bits, but there is some
signed math that should be unsigned.

-- Terry

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