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[Xen-devel] Re: Where do we stand with the Xen patches?

Ian Campbell wrote:
On Wed, 2009-05-20 at 00:30 +0900, FUJITA Tomonori wrote:
We need these hooks but as I wrote above, they are
architecture-specific and we should handle them with the architecture
abstraction (as we handle similar problems) however we can't due to
dom0 support.

I don't understand this. What exactly about the dom0 support patch
prevents future abstraction here?

The dom0 hooks would simply move into the per-arch abstractions as
appropriate, wouldn't they?

Fujita-san's suggestion to me was that swiotlb could just use the normal (albeit deprecated) phys_to_bus()/bus_to_phys() interfaces rather than defining its own. That would be perfectly OK for Xen; we have a single global translation which is unaffected by the target device, etc.

But I'm not sure it would work for powerpc; Becky's patches which added swiotlb_bus_to_phys/phys_bus made them take a device argument, because (apparently) the bus/phys offset can differ on a per-device or per-bus basis. The powerpc side of swiotlb doesn't seem to be in mainline yet, so I'm not sure what the details are here (maybe it can be handled with a single big runtime switch, if the offset is always constant on a given machine).

(Hm, now that I look I see that they're defined as virt_to_bus/bus_to_virt, which doesn't work for highmem at all; it would need to be phys.)

But I may have misinterpreted what he meant.

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