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[Xen-devel] Re: mthca use of dma_sync_single is bogus
> > void
> > dma_sync_single_range(struct device *dev, dma_addr_t dma_handle,
> > unsigned long offset, size_t size,
> > enum dma_data_direction direction)
> This is under Part II - Advanced dma_ usage - I don't think it's dealing with
> non-consistent memory only (e.g. dma_declare_coherent_memory is there), and
> looks like a good fit. Most functions here work for both consistent and
> non-consistent memory... What makes you suspicious?
I was suspicious because it is described between the main noncoherent
API stuff and dma_cache_sync(). But I think it is probably OK.
Unfortunately it is not that good a fit for our current code, since we
use pci_map_sg() to do the DMA mapping on the MTT memory instead of
> I'm concerned that MTTs need a fair amount of memory,
> while the amount of coherent memory might be limited.
> Not that non-coherent memory systems are widespread ...
Yes, for example on ppc 4xx the amount of coherent memory is quite
small by default (address space for non-cached mappings is actually
what is limited, but it amounts to the same thing).
Maybe the least bad solution is to change to using dma_map_single()
instead of pci_map_sg() in mthca_memfree.c.
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