Re: [Xen-devel] USB virt status --- Help please!!!

[harry <harry@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx>]

On Mon, 2005-11-14 at 10:12 +0000, harry wrote:
> On Mon, 2005-11-14 at 09:56 +0000, Keir Fraser wrote:
> > On 13 Nov 2005, at 18:28, Harry Butterworth wrote:
> > 
> > > Is this the right approach? Is the check in dma_map_single overzealous?
> > 
> > When running on Xen, just because Linux has allocated adjacent pages 
> > from its 'physical' memory map, doesn't mean they really are physically 
> > contiguous. For I/O we have to go to extra effort to really allocate 
> > truly contiguous multi-page extents.
> > 
> > So your code is correct. If you can preallocate buffers then you could 
> > do that with dma_alloc_coherent and that would guarantee contigous 
> > buffers....
> 
> I'm given the buffers by the assorted USB drivers.  I could stage the
> data using memcpy into my own buffer allocated using dma_alloc_coherent.
> Or should I go through all the USB drivers and change the buffer
> allocation?

It looks like there is an operation usb_buffer_alloc which I can
implement to give the right kind of buffers to clients.  Any buffers not
allocated from here can be staged.  Should hopefully be OK.



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