Re: [RFC PATCH] xen/amd-iommu: Add interrupt remapping quirk for ath11k

["Roger Pau Monné" <roger.pau@citrix.com>]

On Thu, Mar 13, 2025 at 11:30:28AM -0400, Jason Andryuk wrote:
> On 2025-02-27 05:23, Roger Pau Monné wrote:
> > On Wed, Feb 26, 2025 at 04:11:25PM -0500, Jason Andryuk wrote:
> > > 
> > > The ath11k device supports and tries to enable 32 MSIs.  Linux in PVH
> > > dom0 and HVM domU fails enabling 32 and falls back to just 1, so that is
> > > all that has been tested.
> > 
> > DYK why it fails to enable 32?
> 
> In Linux msi_capability_init()
> 
>         /* Reject multi-MSI early on irq domain enabled architectures */
>         if (nvec > 1 && !pci_msi_domain_supports(dev,
> MSI_FLAG_MULTI_PCI_MSI, ALLOW_LEGACY))
>                 return 1;
> 
> MSI_FLAG_MULTI_PCI_MSI is only set for AMD and Intel interrupt remapping,
> and Xen PVH and HVM don't have either of those.  They are using "VECTOR", so
> this check fails.

Oh, interesting.  So classic PV MSI domain supports
MSI_FLAG_MULTI_PCI_MSI, even when no IOMMU is exposed there either.

Thanks, so it's nothing specific to Xen, just how Linux works.

Roger.