Attached are the HCL results of my Ryzen system.
It did NOT work out of the box on Qubes - IOMMU was not available. However, Ubuntu stated it's working (BIOS IOMMU looks great) so I played around a bit.
Basically, two things are needed for working IOMMU in Xen used by Qubes:
1) Update Xen with an IOMMU patch from AMD
2) Update Xen with family 17h == Ryzen
For step 1): Apply this patch (part or Xen 4.8.0): https://patchwork.kernel.org/patch/9145119/
For step 2): xen/arch/x86/oprofile/nmi_int.c - Create a "case 0x17:" entry which is the same as "case 0x15:"
I installed Qubes, then proceeded as described to compile Qubes from scratch. Before I did "make vmm-xen" I changed the above files within the xen*.gz file. After that, I moved the files to dom0 and forced a reinstall of the RPM files.
Rebooted and voila, you can see the resul in the files :) Now I can get a TPM I guess ;)
I posted this nmi_int.c patch also on the xen-devel mailing list, let's see if it's enough for them.
Maybe these two patches can be added to Qubes 3.2 (if they work properly). Not sure if there is anything else I can do to test if IOMMU is working properly, if something is there to test that please let me know!