mpt2sas DMA mask

[Benjamin Herrenschmidt]

On Tue, 2015-05-12 at 17:07 -0500, Brian King wrote:
> The mpt2sas driver was changed late last year in that it now requests a 64 bit DMA
> mask, then requests a 32 bit coherent DMA mask, then later requests a 64 bit coherent
> DMA mask. This was 5fb1bf8aaa832e1e9ca3198de7bbecb8eff7db9c. This breaks 64 bit DMA
> support for mpt2sas on Power and we always fall back to using 32 bit DMA. Looking
> at the commit log, it looks like this was an intentional change.
> 
> Ben - you had a patch set you had posted to the list back in Feb of this year, but it
> doesn't look like it got merged. 

Right, it was broken, we can't do that unfortunately. It's a hard
problem to fix.

> https://lists.ozlabs.org/pipermail/linuxppc-dev/2015-February/125087.html
> 
> This would fix the issue I'm seeing on mpt2sas. Do you plan to dust that patch set
> off and upstream it? Were there issues with it that still need to be resolved?

No that patch doesn't actually work.

What we need is essentially a new set of DMA ops that can route an
individual map request via the iommu or the bypass window depending on
what mask applies.

Ben.