Subject: Re: [bug report] powerpc: per device MSI irq domain

From: Nam Cao <[email-masked]>
Date: Thu, 04 Dec 2025 11:48:24 +0100

Hi Nilay,

Nilay Shroff <[email-masked]> writes:
> I have been using an NVMe disk on my PowerPC system that supports up to
> 129 MSI-X interrupt vectors. Everything worked fine until Linux kernel
> v6.18, after which the NVMe driver stopped detecting the disk because
> the driver probe now fails.
>
> After further investigation, I found that the probe failure in v6.18
> occurs during PCI/MSI-X vector allocation. A git bisect identified
> commit daaa574aba6f (“powerpc/pseries/msi: Switch to msi_create_parent_
> irq_domain()”) as the first bad commit.

Thanks for the report. I can (kind of) reproduce the problem with QEMU.

I think moving rtas_prepare_msi_irqs() into pseries_irq_domain_alloc()
should resolve the problem. But I'm not sure because I don't understand
how RTAS works.

Does IBM have some documentation describing the RTAS API? I failed to
google it.

Best regards,
Nam