On Mon, Aug 11, 2025 at 07:39:35AM +0200, Nam Cao wrote:
> Commit d7d8ab87e3e7 ("PCI: vmd: Switch to msi_create_parent_irq_domain()")
> added a WARN_ON sanity check that child devices support MSI-X, because VMD
> document says [1]:
>
> "Intel VMD only supports MSIx Interrupts from child devices and
> therefore the BIOS must enable PCIe Hot Plug and MSIx interrups [sic]."
Can VMD tell the difference between an incoming MSI MWr transaction
and an MSI-X MWr?
I wonder if "MSIx" was meant to mean "VMD only supports MSI or MSI-X
interrupts, not INTx interrupts, from child devices"?
I put this on pci/for-linus for v6.17, but it seems like we might want
to clarify the commit log.
> However, on Ammar's machine, a PCIe port below VMD does not support MSI-X,
> triggering this WARN_ON.
>
> This inconsistency between the document and reality should be investigated
> further. For now, remove the MSI-X check.
>
> Allowing child devices without MSI-X despite what the document says does
> sound suspicious, but that's what the driver had been doing before the
> WARN_ON is added.
>
> Fixes: d7d8ab87e3e7 ("PCI: vmd: Switch to msi_create_parent_irq_domain()")
> Link: https://cdrdv2-public.intel.com/776857/VMD_White_Paper.pdf [1]
> Reported-by: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx>
> Closes: https://lore.kernel.org/linux-pci/aJXYhfc%2F6DfcqfqF@xxxxxxxxxxxxxxxxx/
> Tested-by: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx>
> Signed-off-by: Nam Cao <namcao@xxxxxxxxxxxxx>
> ---
> drivers/pci/controller/vmd.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index b679c7f28f51..1bd5bf4a6097 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -306,9 +306,6 @@ static bool vmd_init_dev_msi_info(struct device *dev, struct irq_domain *domain,
> struct irq_domain *real_parent,
> struct msi_domain_info *info)
> {
> - if (WARN_ON_ONCE(info->bus_token != DOMAIN_BUS_PCI_DEVICE_MSIX))
> - return false;
> -
> if (!msi_lib_init_dev_msi_info(dev, domain, real_parent, info))
> return false;
>
> --
> 2.39.5
>
