From: Jonathan Gray <jsg@jsg.id.au>
Subject: Re: PCI amd64: Enables MSI/MSI-X interrupts on QEMU i440fx chipset emulation
To: Yuichiro NAITO <naito.yuichiro@gmail.com>
Cc: kettenis@openbsd.org, tech@openbsd.org, yasuoka@openbsd.org
Date: Mon, 7 Oct 2024 13:29:06 +1100

On Mon, Oct 07, 2024 at 10:54:14AM +0900, Yuichiro NAITO wrote:
> Hi, this patch sets 'PCI_FLAGS_MSI_ENABLED' if the kernel runs on a QEMU
> virtual machine with i440fx chipset emulation. The i440fx is the default
> chipset on the QEMU so users will use it first.
> And then ixv(4) and iavf(4) will fail because MSI-X interrupts are not
> supported by the kernel.
> 
> The i440fx is quite old and the ACPI table is revision 1. We cannot know
> if it has MSI capability from the ACPI table. So I add the flag as a quirk.

i440fx was released in 1996.  Why not use the q35/ich9 machine?
That hardware had MSI.

If networking is configured, non-default options are already set.

> 
> The same quirk is implemented in NetBSD.
> 
> https://github.com/NetBSD/src/blob/affb7619d18b17a184eede63a4823f629a2893fc/sys/arch/x86/pci/pci_machdep.c#L273
> 
> FreeBSD seems to have the quirk but is used as the exception for blacklist
> devices. Probably they see the PCI device capability header of MSI/MSI-X.
> Until we see the same capability, my patch will be useful for the VF driver
> users.
> 
> OK?
> 
> diff --git a/sys/arch/amd64/pci/pci_machdep.c b/sys/arch/amd64/pci/pci_machdep.c
> index 30257ab7d82..4a49c898e96 100644
> --- a/sys/arch/amd64/pci/pci_machdep.c
> +++ b/sys/arch/amd64/pci/pci_machdep.c
> @@ -170,6 +170,31 @@ void
>  pci_attach_hook(struct device *parent, struct device *self,
>      struct pcibus_attach_args *pba)
>  {
> +	pci_chipset_tag_t pc = pba->pba_pc;
> +	pcitag_t tag;
> +	pcireg_t id, class;
> +
> +	if (pba->pba_bus != 0)
> +		return;
> +
> +	tag = pci_make_tag(pc, 0, 0, 0);
> +	id = pci_conf_read(pc, tag, PCI_ID_REG);
> +	class = pci_conf_read(pc, tag, PCI_CLASS_REG);
> +
> +	if (PCI_CLASS(class) != PCI_CLASS_BRIDGE ||
> +	    PCI_SUBCLASS(class) != PCI_SUBCLASS_BRIDGE_HOST)
> +		return;
> +
> +	/*
> +	 * QEMU uses the old chipset i440fx by default, but it can use
> +	 * MSI/MSI-X interrupt. We cannot know if MSI/MISX is available
> +	 * from the ACPI table. Because it's quite old style (revision 1).
> +	 */
> +	if ((cpu_ecxfeature & CPUIDECX_HV) &&
> +	    PCI_VENDOR(id) == PCI_VENDOR_INTEL &&
> +	    PCI_PRODUCT(id) == PCI_PRODUCT_INTEL_82441FX) {
> +		pba->pba_flags |= PCI_FLAGS_MSI_ENABLED;
> +	}
>  }
>  
>  int
> 
> -- 
> Yuichiro NAITO (naito.yuichiro@gmail.com)
> 
>