[parisc-linux] EISA 100/10 add-on card causes kernel BUG

[Matthew Wilcox]

On Sat, Mar 16, 2002 at 10:38:38PM -0700, Grant Grundler wrote:
> oh - I forgot about those for filling the IO pdir entries...
> that need to change in order to support zero copy?
> 
> We somehow need to pass the spaceID of the userspace buffer
> to dma code if we want DMA to be cache coherent.
> I don't have any good ideas for this.

My understanding is that DMA to userspace is to pages in the page cache
only.  As such, the normal mechanisms for dcache coherency should be used.
That is, DMA to a kernel view of the page and call flush_dcache_page
after touching it.  My proposed scheme for kmap/kunmap implementation
would make flush_dcache_page a no-op, since the kernel would have a view
of the page which is automatically cache coherent with userspace's view.

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