Coherent bus_dma for ARMv7

[Andrew Turner]

> On 3 Apr 2017, at 14:16, Marcin Wojtas <mw at semihalf.com> wrote:
> 
> Hi Adrian,
> 
> Frankly we are not such experts in armv6 bus_dma, which looks more
> complicated than one in arm64, so we thought it's much safer no to mix
> the two solutions and leave for the user a single switch to decide,
> which one to pick. Afaik Andrew Turner did the oposite for arm64
> (implement not coherent solution on top of coherent bus_dma), however
> I'm not sure if it's possible here in an easy way - there's also
> pretty significant risk of regression for all platforms. Please let me
> know your opinion. Do you think some sort of update of armv6 is
> doable?

I don’t see any reason to think it would be difficult to add support for coherent hardware to the existing armv6 busdma code. It’s mostly skipping cache operations based on a flag in the dam tag.

Andrew