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RE: [Xen-devel] Xen 3.0 Status update

> bttv tries to allocate buffers from ZONE_NORMAL (i.e. avoid 
> highmem) in case it has control over the allocations, which 
> is far from being perfect.  Works reliable only on 32 bit, 
> doesn't work on 64-bit without iommu and >4GB for example ...

Yep, for pages for actual data-path transfers there's nothing better we
can do than use the iommu (or s/w implementation their of).

However, for the long-lived control regions used by some devices (e.g.
for descriptor rings etc) it probably makes sense to try and allocate
them in memory they can access directly. Some of these have daft
restrictions, such as the aacraid device only being able to use memory
below 2GB for its control program.

Most of these regions are bigger than a page so have to be created with
dma_alloc_coherent, hence we have an opportunity to allocate them in a
region they can directly access.


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