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xen-devel
Re: [Xen-devel] Failure to get memory for GATT table, again
On Tue, Feb 01, 2005 at 10:45:49PM +0000, Ian Pratt wrote:
>
> > hmm, actually it seems the case is that dma_alloc_coherent() falls back to
> > calling __get_free_pages(), because dev->dma_mem is NULL. When the returned
> > address gets converted into a bus address, the resulting address seems to
> > be
> > within Xen-space :-(
> >
> > Why is calling __get_free_pages() a problem?
>
> The AGP aperture needs a set of machine contiguous pages, whereas
> get_free_pages will only give you pseudo-physical contiguous.
>
> Drivers are supposed to use the former (for reasons of ensuring
> DMA coherence) , but the agp drivers seem particularly shoddy,
> probably because they've only ever been used on x86.
Hmm but it seems that dev->dma_mem is never set for the device, causing a
fallback to
__get_free_pages(). Should the driver have set this?
Jacob
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