AMD GPUs on the Altra devkit and other Altras - patches available now

q66 · May 27, 2023, 2:59am

Hi,

I’ve made it possible to use AMD GPUs on the Altras without graphical glitches.
As it turns out, the Altra has a buggy PCIe controller, which means you can
technically modeset with the GPUs and launch a desktop, but you will get
garbage in the output, like this:

I’ve come across some patches in Tencent’s kernel tree, which is a fork of
an old LTS. The patches do not apply on modern kernels:

github.com/Tencent/TencentOS-kernel

ampere/arm64: Add a fixup handler for alignment faults in aarch64 code

committed 04:21PM - 05 Jul 21 UTC

+745 -0

A later patch will hand out Device memory in some cases to code which expects a …Normal memory type, as an errata workaround. Unaligned accesses to Device memory will fault though, so here we add a fixup handler to emulate faulting accesses, at a performance penalty. Many of the instructions in the Loads and Stores group are supported, but these groups are not handled here: * Advanced SIMD load/store multiple structures * Advanced SIMD load/store multiple structures (post-indexed) * Advanced SIMD load/store single structure * Advanced SIMD load/store single structure (post-indexed) * Load/store memory tags * Load/store exclusive * LDAPR/STLR (unscaled immediate) * Load register (literal) [cannot Alignment fault] * Load/store register (unprivileged) * Atomic memory operations * Load/store register (pac) Instruction implementations are translated from the Exploration tools' ASL specifications. Signed-off-by: D Scott Phillips <scott@os.amperecomputing.com>

I ended up rebasing them, however:

For 6.1: main/linux-lts: update to 6.1.30 and fix GPUs on ampere altra · chimera-linux/cports@da73b68 · GitHub
for 6.3: main/linux-stable: update to 6.3.4 and fix GPUs on ampere altra · chimera-linux/cports@38692a6 · GitHub

Now you get this:

You just need to apply them into the kernel. The kernels in my distribution
will come patched out of the box, people on other distributions will need
to apply it and rebuild their kernel. Mesa does not need to be rebuilt,
it works as is.

Tested GPUs are Radeon Pro WX 2100 (works out of the box, any kernel version, as long as patched) and Radeon RX 5500 XT (needs kernel 6.2 or newer, just like everything newer than AMD Polaris, as before 6.2 the DC component was not ready on AArch64 due to kernel hardware floating point trouble, and also kernel command line parameters pcie_aspm=off amdgpu.aspm=0 amdgpu.runpm=0).

Note that these patches are a workaround and come with a performance penalty,
especially when unaligned access is involved. However, things run quite
satisfactorily as far as I can tell.

Aaron · May 27, 2023, 5:24pm

@q66 thank you for the post, that is awesome…

kkrysa · May 29, 2023, 1:39pm

Thanks a lot for sharing @q66 and an even bigger thanks for the solution itself!

I really hope the forum gets more people writing about their personal projects or anything AArch64-related done as a part of their regular work.

Even outside our group, there’s a lot of great stuff going on that I’m sure many end up reading about and not everyone here is necessarily aware of.