While we won't know for sure, unless someone from AMD comments on this; in fairness there may not have been any other way.
Nvidia has a large number of GPU related patents.
The fact that AMD chose to design their system this way, in such a roundabout and brittle manner, which is contrary to how engineer's approach things, may have been a direct result of being unable to design such systems any other way because of broad patents tied to the interface/GPU.
> why so few of AMD's GPUs have official ROCm support
Because "official ROCm support" means "you can rely on AMD to make this work on your system for your critical needs". If you want "support" in the "you can goof around with this stuff on your own and don't care if there's any breakage" sense, ROCm "supports" a whole lot of AMD hardware. They should just introduce a new "experimental, unsupported" tier and make this official on their end.
> I feel like this issue is to at least some extent a red herring.
I don't see that, these two issues adequately explain why so few GPUs have official support. They don't want to get hit with a lawsuit, as a result of issues outside their sphere of control.
> If this really is due to patent issues AMD can likely afford to license or cross-license the patent given potential upside.
Have you ever known any company willing to cede market dominance and license or cross-license a patent letting competition into a market that they hold an absolute monopoly over, let alone in an environment where antitrust is non-existent and fang-less?
There is no upside for NVIDIA to do that. If you want to do serious AI/ML work you currently need to use NVIDIA hardware, and they can charge whatever they want for that.
The moment you have a competitor, demand is halved at a bare minimum depending on how much the competitor undercuts you by. Any agreement on coordinating prices leads to price-fixing indictments.
> I don't see that, these two issues adequately explain why so few GPUs have official support.
I'm sorry I don't follow this. Surely if all AMD GPUs have the same problem with atomics then this can't explain why some GPUs are supported and others aren't?
> There is no upside for NVIDIA to do that.
If NVIDIA felt this patent was actually protecting them from competition then there would be no upside. But NVIDIA has competiton from AMD, Intel, Google, and Amazon. Intel have managed to engineer OneAPI support for their GPUs without licensing this patent or relying on PCIe atomics.
AMD have patents NVIDIA would be interested in. For example multi-chiplet GPUs.
I feel like this issue is to at least some extent a red herring. Even accepting that ROCm doesn't work on some motherboards, this can't explain why so few of AMD's GPUs have official ROCm support.
I notice that at one point there was a ROCm release which said it didn't require atomics for gfx9 GPUs, but the requirement was reintroduced in a later version of ROCm. Not sure what happened there but this seems to suggest AMD might have had a workaround at some point (though possibly it didn't work).
If this really is due to patent issues AMD can likely afford to licence or cross-license the patent given potential upside.
It would be in line with other decisions taken by AMD if they took this decision because it works well with their datacentre/high-end GPUs, and they don't (or didn't) really care about offering GPGPU to the mass/consumer GPU market.