Re: [PATCH 1/1] drm/amdkfd: fix build error with AMD_IOMMU_V2=m

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

Hi Felix,

On Tue, Mar 09, 2021 at 11:30:19AM -0500, Felix Kuehling wrote:
> > I think the proper fix would be to not rely on custom hooks into a particular
> > IOMMU driver, but to instead ensure that the amdgpu driver can do everything
> > it needs through the regular linux/iommu.h interfaces. I realize this
> > is more work,
> > but I wonder if you've tried that, and why it didn't work out.
> 
> As far as I know this hasn't been tried. I see that intel-iommu has its
> own SVM thing, which seems to be similar to what our IOMMUv2 does. I
> guess we'd have to abstract that into a common API.

The common API was added in 26b25a2b98e4 and implemented by the Intel
driver in 064a57d7ddfc. To support it an IOMMU driver implements new IOMMU
ops:
	.dev_has_feat()
	.dev_feat_enabled()
	.dev_enable_feat()
	.dev_disable_feat()
	.sva_bind()
	.sva_unbind()
	.sva_get_pasid()

And a device driver calls iommu_dev_enable_feature(IOMMU_DEV_FEAT_SVA)
followed by iommu_sva_bind_device().

If I remember correctly the biggest obstacle for KFD is the PASID
allocation, done by the GPU driver instead of the IOMMU driver, but there
may be others.

Thanks,
Jean