linux-kernel - Re: snd-cmipci oops during probe on arm64 (current mainline, pre-6.6-rc1)

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Date:   Wed, 6 Sep 2023 21:41:05 -0300
From:   Antonio Terceiro <antonio.terceiro@...aro.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Takashi Iwai <tiwai@...e.de>, Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: snd-cmipci oops during probe on arm64 (current mainline,
 pre-6.6-rc1)

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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