Remove the dual-address cycle stuff. DAC is used to allow a bus master device to access 64-bit addresses from a 32-bit PCI bus. While the RealTek manual says you can set this bit and the chip will perform DAC only if you give it a DMA address with any of the upper 32 bits set, this appears not to be the case. If I turn on the DAC bit, the chip sets the 'system error' bit in the status register when I to do a DMA on my Athlon test box with 32-bit PCI bus (VIA chipset) even though I only have 128MB of physical memory, and thus can never give the chip a 64-bit address.
Remove the dual-address cycle stuff. DAC is used to allow a bus master
device to access 64-bit addresses from a 32-bit PCI bus. While the
RealTek manual says you can set this bit and the chip will perform
DAC only if you give it a DMA address with any of the upper 32
bits set, this appears not to be the case. If I turn on the DAC
bit, the chip sets the 'system error' bit in the status register
when I to do a DMA on my Athlon test box with 32-bit PCI bus (VIA
chipset) even though I only have 128MB of physical memory, and thus
can never give the chip a 64-bit address.

Obviously, I can't just set it and forget it, so until I figure
out the right rule for when it's safe/necessary to enable it, keep
it turned off.

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