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

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:

quoted

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 
specific?

Jamie