Re: [PATCH 4/4] POWERPC: Merge 32 and 64-bit dma code

On Tue, Sep 09, 2008 at 09:39:20AM -0500, Becky Bruce wrote:

.... because you asked me to have just map/unmap_page in your review  
of an earlier rev of this patch series in May? :)  I don't actually  
expect you to remember this, because it was a long time ago, but  
here's the relevant chunk of the conversation:

On May 23, 2008, at 4:51 AM, Christoph Hellwig wrote:

quoted

On Wed, Apr 30, 2008 at 06:36:43PM -0500, Becky Bruce wrote:

quoted

In addition, the dma_map/unmap_page functions are added to dma_ops on
HIGHMEM-enabled configs because we can't just fall back on map/ 
unmap_single
when HIGHMEM is enabled.  Adding these to dma_ops makes it cleaner to
substitute different functionality once we have iommu/swiotlb  
support.

Maybe I'm missing something but we should only have the page ones.
virt_to_page is cheap and we'll most likely need the phys address  
which
we get from the page anyway.

So I did that for the dma_direct_* ops, but discovered that doing it  
for the iommu case (which I can't test and don't fully understand)  
would be a bit more complicated.  The above code (in conjunction with  
the same code for map_page) allows you to have map/unmap_page, map/ 
unmap_single, or both.  I'm happy to change it again, though.  We  
could just do the above in map_page/unmap_page, calling map/ 
unmap_single if there is no map/unmap_page, and provide both a  
dma_direct_map/unmap_single and a dma_direct_map/unmap_page for the  
dma_direct* ops.

Yeah, the statement this time should be why do you keep _single :)
It don't really mind which one we keep, but having both and both
optional seems rather odd.