On Wed, Sep 06, 2023 at 08:52:40PM +0100, Robin Murphy wrote: > On 2023-09-06 19:36, Antonio Terceiro wrote: > > I'm pretty sure I saw reports of people using PCI GPUs on this machine, > > but I would need to confirm. > > GPUs and any other PCIe devices will be fine, since they will use memory > BARs - I/O space is pretty much deprecated in PCIe, and as mentioned some > systems don't even support it at all. I found a datasheet for CMI8738, and > they seem to be right at the other end of the scale as legacy PCI chips with > *only* an I/O BAR (and so I guess your card includes a PCIe-PCI bridge as > well), so are definitely going to be hitting paths that are less > well-exercised on arm64 in general. OK, that makes sense. So If I'm able to find a card that is genuinely PCIe¹, then it should work? ¹ this one has a connector that looks like a PCIe x1, but it's not really PCIe as the chipset was designed for legacy PCI? > > What info would I need to gather from the machine in order to figure > > this out? > > The first thing I'd try is rebuilding the kernel with CONFIG_INDIRECT_PIO > disabled and see what difference that makes. I'm not too familiar with that > area of the code, so the finer details of how to debug broken I/O space > beyond that would be more of a linux-pci question. Tried that, didn't help.
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