Re: [PATCH v2 8/8] habanalabs: enable 64-bit DMA mask in POWER9

From: Christoph Hellwig
Date: Wed Jun 12 2019 - 02:57:51 EST

On Wed, Jun 12, 2019 at 04:35:22PM +1000, Oliver O'Halloran wrote:
> Setting a 48 bit DMA mask doesn't work today because we only allocate
> IOMMU tables to cover the 0..2GB range of PCI bus addresses.

I don't think that is true upstream, and if it is we need to fix bug
in the powerpc code. powerpc should be falling back treating a 48-bit
dma mask like a 32-bit one at least, that is use dynamic iommu mappings
instead of using the direct mapping. And from my reding of
arch/powerpc/kernel/dma-iommu.c that is exactly what it does.