linux-kernel - amd iommu configuration

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Date:   Thu, 01 Sep 2022 14:36:20 -0400
From:   Steven J Abner <pheonix.sja@....net>
To:     linux-kernel@...r.kernel.org
Subject: amd iommu configuration

Hi
Building a kernel tailored for AMD 2400g on ASRock B450 using 5.18.12 
as base.
I stumbled across an odd situation and which lacked Kconfig info and 
lead to oddity.
/drivers/iommu/amd/Kconfig states 'config AMD_IOMMU_V2' is 'tristate' 
but unlike many
other tristate configures doesn't mention that module name is 
'iommu_v2.ko' and loading should be done by adding to modules-load.d.

The oddity is that by loading as module is as follows (differences):

builtin iommu_v2 version dmesg:
amdgpu: HMM registered 2048MB device memory
amdgpu: Topology: Add APU node [0x0:0x0]
amdgpu: Topology: Add APU node [0x15dd:0x1002]
AMD-Vi: AMD IOMMUv2 loaded and initialized
kfd kfd: amdgpu: added device 1002:15dd
kfd kfd: amdgpu: Allocated 3969056 bytes on gart
memmap_init_zone_device initialised 524288 pages in 0ms

module not loaded due to missing iommu.conf dmesg:
amdgpu: CRAT table disabled by module option
amdgpu: Topology: Add CPU node
amdgpu: Virtual CRAT table created for CPU
kfd kfd: amdgpu: GC IP 090100 not supported in kfd

module load through iommu.conf dmesg:
amdgpu: CRAT table disabled by module option
amdgpu: Topology: Add CPU node
amdgpu: Virtual CRAT table created for CPU
AMD-Vi: AMD IOMMUv2 loaded and initialized
kfd kfd: amdgpu: GC IP 090100 not supported in kfd

Note, only difference on witk/without iommu.conf is:
AMD-Vi: AMD IOMMUv2 loaded and initialized

So does this mean missing features by not having builtin?
If not, should Kconfig have hint about module and loading?

Steve

I wish to be personally CC'ed the answers/comments posted to the list
in response to my posting, please:) Not a list member.