Re: [PATCH] ahci: force 32-bit DMA for JMicron JMB582/JMB585

[Mikael Etienne <mikael1022bzh@gmail.com>]

Hi Niklas,

You asked whether there might be different versions of the AMD IOMMU. Here is my
full identification, so this can be compared rather than guessed:

  CPU        : AMD Ryzen 7 8700G w/ Radeon 780M (Phoenix), family 25, model 117,
               stepping 2
  Controller : AMD 600 Series Chipset SATA Controller [1022:43f6]
  Table      : ACPI IVRS v02 (AMD / AmdTable)
  IVHD       : AMD-Vi: Using global IVHD EFR:0x246577efa2254afa, EFR2:0x0
  Kernel     : 7.1.x, Fedora 44

The EFR field is probably the most direct discriminant. If Arthur, Alvin and
Lennert posted the same line, the "different IOMMU versions" hypothesis could be
tested immediately, with no extra hardware:

  journalctl -k -b | grep -E "IVHD EFR|IVRS"

That would be particularly worth it for Alvin, since iommu=pt is insufficient
for him while it is completely clean for me -- that is the only divergence
between our reports.

I cannot be your tester for point 1, unfortunately: I have neither a JMB582/585
nor an Intel or ARM IOMMU. The reproducer you quoted is current; one
clarification, fio verifies its own CRC32C, so the result does not depend on the
underlying filesystem.

On your point 2: I am working with Mario on the AMD IOMMU side. I have committed
to testing on my 600-series and reporting the outcome in the regression thread,
positive or negative. I cannot give a date -- the machine is under maintenance
work -- but I will report either way.

Kind regards,
Mikael Etienne