Re: [Xen-devel] Failure to get memory for GATT table, again

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> 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.

Ian


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