PCI: vmd: Remove MSI-X check on child devices

d7d8ab8 ("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].

However, the VMD device can't even tell the difference between a child
device using MSI and one using MSI-X.  Per 185a383 ("x86/PCI: Add
driver for Intel Volume Management Device (VMD)"), VMD does not support
INTx interrupts, but does support child devices using either MSI or MSI-X.

Remove the sanity check to avoid the WARN_ON and allow child devices to use
MSI, reported by Ammar.

Fixes: d7d8ab8 ("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 <[email protected]>
Closes: https://lore.kernel.org/linux-pci/aJXYhfc%[email protected]/
Signed-off-by: Nam Cao <[email protected]>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <[email protected]>
Tested-by: Ammar Faizi <[email protected]>
Link: https://patch.msgid.link/[email protected]

Author: covanam

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;