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

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

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. 

   J

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