[PATCH 11/13] drm/amdgpu: add DRM_AMDGPU_ATC config option

[Christian König]

Am 29.01.2018 um 23:08 schrieb Felix Kuehling:
> On 2018-01-26 03:13 PM, Christian König wrote:
>> [SNIP]
>> +#ifdef CONFIG_DRM_AMDGPU_ATC
>> +	r = amd_iommu_init_device(adev->pdev, 0x10000);
> KFD queries how many PASIDs the IOMMU can support with
> amd_iommu_device_info. KFD only assigns PASIDs within that range. It can
> be much smaller than the 16-bits supported by the GPU.
>
> For a VM that uses ATC, you need to make sure it gets a PASID in the
> range supported by the IOMMU. The PASID manager already supports that
> and keeps smaller PASIDs for users that really need them.

Yeah, seen that and I'm not really keen about it.

Especially since we need multiple types of PASIDs here:
1. For GPUVM debugging and HMM faults, where we can use the full 16bit 
range without worrying about what IOMMU can do.
2. For ATC use case where we need to keep the IOMMU in the picture.

Are there any hardware limitations which blocks us from using a per 
device PASID? That would simplify the whole handling quite a bit.

Additional to that we don't really want this direct relationship between 
amdgpu/amdkfd and the amd_iommu_v2 driver.

So what do you think about moving the PASID handling into the IOMMU 
driver? And abstracting which driver is in use through the iommu_ops?

Regards,
Christian.

>
> Regards,
>    Felix