AMD IOMMU perf counters on Zen2

[Alexander Monakov]

Hello,

I'd like to use IOMMU perf counters on a Zen 2 CPU (Ryzen 4500U, Renoir SoC).
Unfortunately, init_iommu_perf_ctr fails because val2 != val, i.e. the
counter appears not writable. However, if I patch the kernel to skip this
check, the counters seem to increment when configured with perf tool.

Do you know why the counter might appear not writable in newer CPUs?

Thanks.
Alexander