Re: pci_dma64_available() and Xen

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

On Sat, Oct 11, 2008 at 10:58:54PM +0200, Manuel Bouyer wrote:
> This is wrong for Xen, where a domain may have less than 4GB allocated,
> but its memory is above the 4GB limit. More generally, this seems to
> assume that the physical memory is contigous, which I feel is wrong for a
> MI piece of code.

It doesn't have to be contigous, but I think all practical platforms
have it semi-contiguous from low addresses. The test is bogus, but not
useless. The intention is to avoid the overhead of 64bit DMA if all bus
addresses will be below 4GB. physmem a good approximation for most
cases, but of course not correct. Best approach is to likely make it a
global variable (pci_prefer_32bit) for 64bit platforms to express the
intend. Just removing the conditional is not good though.

Joerg