Re: [PATCH 01/19] dma-mapping: add a Kconfig symbol to indicated arch_dma_prep_coherent presence

[Christoph Hellwig]

On Fri, Feb 01, 2019 at 02:22:46PM +0000, Robin Murphy wrote:
> On 14/01/2019 09:41, Christoph Hellwig wrote:
>> Add a Kconfig symbol that indicates an architecture provides a
>> arch_dma_prep_coherent implementation, and provide a stub otherwise.
>>
>> This will allow the generic dma-iommu code to it while still allowing
>> to be built for cache coherent architectures.
>
> I've been pondering this for a while now, and I still can't really come up 
> with a case where arch_dma_prep_coherent() would need to behave differently 
> from arch_sync_dma_for_device(..., DMA_BIDIRECTIONAL). I wonder if we could 
> just save ourselves this little bit of complexity by using that instead...

A lot of architectures do really weird stuff in the dma sync routines.
So my plan would be to consolidate a lot more logic in there first,
and then maybe as a next step we could look into using
arch_sync_dma_for_device eventually.