Subject: Re: [PATCH 1/5] iommu: Replace uses of IOMMU_CAP_CACHE_COHERENCY with dev_is_dma_coherent()

From: Jason Gunthorpe <[email-masked]>
Date: Wed, 6 Apr 2022 11:14:46 -0300

On Wed, Apr 06, 2022 at 03:51:50PM +0200, Christoph Hellwig wrote:
> On Wed, Apr 06, 2022 at 09:07:30AM -0300, Jason Gunthorpe wrote:
> > Didn't see it
> > 
> > I'll move dev_is_dma_coherent to device.h along with
> > device_iommu_mapped() and others then
> 
> No.  It it is internal for a reason.  It also doesn't actually work
> outside of the dma core.  E.g. for non-swiotlb ARM configs it will
> not actually work.

Really? It is the only condition that dma_info_to_prot() tests to
decide of IOMMU_CACHE is used or not, so you are saying that there is
a condition where a device can be attached to an iommu_domain and
dev_is_dma_coherent() returns the wrong information? How does
dma-iommu.c safely use it then?

In any case I still need to do something about the places checking
IOMMU_CAP_CACHE_COHERENCY and thinking that means IOMMU_CACHE
works. Any idea?

Jason