VT-d: correct ATS checking for root complex integrated devices

Spec version 4.1 says

"The ATSR structures identifies PCI Express Root-Ports supporting
 Address Translation Services (ATS) transactions. Software must enable
 ATS on endpoint devices behind a Root Port only if the Root Port is
 reported as supporting ATS transactions."

Clearly root complex integrated devices aren't "behind root ports",
matching my observation on a SapphireRapids system having an ATS-
capable root complex integrated device. Hence for such devices we
shouldn't try to locate a corresponding ATSR.

Since both pci_find_ext_capability() and pci_find_cap_offset() return
"unsigned int", change "pos" to that type at the same time.

Fixes: 903b93211f ("[VTD] laying the ground work for ATS")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
master commit: 04e31583ba
master date: 2024-05-06 09:22:45 +0200

xen/drivers/passthrough/vtd/x86/ats.c

@@ -44,7 +44,7 @@ struct acpi_drhd_unit *find_ats_dev_drhd(struct vtd_iommu *iommu)
 int ats_device(const struct pci_dev *pdev, const struct acpi_drhd_unit *drhd)
 {
     struct acpi_drhd_unit *ats_drhd;
-    int pos;
+    unsigned int pos, expfl = 0;
 
     if ( !ats_enabled || !iommu_qinval )
         return 0;
@@ -53,7 +53,12 @@ int ats_device(const struct pci_dev *pdev, const struct acpi_drhd_unit *drhd)
          !ecap_dev_iotlb(drhd->iommu->ecap) )
         return 0;
 
-    if ( !acpi_find_matched_atsr_unit(pdev) )
+    pos = pci_find_cap_offset(pdev->sbdf, PCI_CAP_ID_EXP);
+    if ( pos )
+        expfl = pci_conf_read16(pdev->sbdf, pos + PCI_EXP_FLAGS);
+
+    if ( MASK_EXTR(expfl, PCI_EXP_FLAGS_TYPE) != PCI_EXP_TYPE_RC_END &&
+         !acpi_find_matched_atsr_unit(pdev) )
         return 0;
 
     ats_drhd = find_ats_dev_drhd(drhd->iommu);