[PATCH 1/2] ARM: convert dma-mapping to asm-generic API

Jamie Iles jamie at jamieiles.com
Tue Dec 21 11:04:49 EST 2010

On Tue, Dec 21, 2010 at 11:01:35AM +0000, Jamie Iles wrote:
> On Tue, Dec 21, 2010 at 10:36:52AM +0000, Russell King - ARM Linux wrote:
> > I don't believe that the direction taken there is anywhere near the right
> > one - the approach we have (implementing the whole buffer sync in terms
> > of the partial buffer sync) is the far more logical, simpler and safer
> > way, and doesn't lead to the possibility of two partially overlapping
> > mappings causing the wrong one to be operated upon.
> > 
> > The debug code doesn't check for overlapping mappings in any way, so we
> > can't say that they never occur.
> >
> > With the way that the DMA API has gone, I view the "generic" stuff as
> > a disaster.
> Ok I can't disagree with that. I've had a look at some of the other 
> arches and I can't see an obvious reason why we couldn't change the 
> generic implementation to do the sync in the way you describe. Perhaps 
> I'll have a look at that after the holidays.

As an alternative, how about we add sync_single_range_for_{cpu,device}() 
methods to struct dma_map_ops and if they aren't populated, fall back to 
the non-range variants with an offset of 0?  Then for ARM we can specify 
the _range_* versions and we don't need the fuzziness in the dmabounce 
code. Or is this just not worth doing and keeping the ARM version 


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