PCI/ATS: Add pci_pri_supported() to check device or associated PF

For SR-IOV, the PF PRI is shared between the PF and any associated VFs, and
the PRI Capability is allowed for PFs but not for VFs. Searching for the
PRI Capability on a VF always fails, even if its associated PF supports
PRI.

Add pci_pri_supported() to check whether device or its associated PF
supports PRI.

[bhelgaas: commit log, avoid "!!"]
Fixes: b16d0cb9e2fc ("iommu/vt-d: Always enable PASID/PRI PCI capabilities before ATS")
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ashok Raj <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>
Reviewed-by: Lu Baolu <[e-mail]>
Acked-by: Joerg Roedel <[e-mail]>
Cc: [e-mail] # v4.4+

drivers/iommu/intel/iommu.c

···
 			}
 
 			if (info->ats_supported && ecap_prs(iommu->ecap) &&
-			    pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI))
+			    pci_pri_supported(pdev))
 				info->pri_supported = 1;
 		}
 	}

drivers/pci/ats.c

···
 
 	return pdev->pasid_required;
 }
+
+/**
+ * pci_pri_supported - Check if PRI is supported.
+ * @pdev: PCI device structure
+ *
+ * Returns true if PRI capability is present, false otherwise.
+ */
+bool pci_pri_supported(struct pci_dev *pdev)
+{
+	/* VFs share the PF PRI */
+	if (pci_physfn(pdev)->pri_cap)
+		return true;
+	return false;
+}
+EXPORT_SYMBOL_GPL(pci_pri_supported);
 #endif /* CONFIG_PCI_PRI */
 
 #ifdef CONFIG_PCI_PASID

include/linux/pci-ats.h

···
 void pci_disable_pri(struct pci_dev *pdev);
 int pci_reset_pri(struct pci_dev *pdev);
 int pci_prg_resp_pasid_required(struct pci_dev *pdev);
+bool pci_pri_supported(struct pci_dev *pdev);
+#else
+static inline bool pci_pri_supported(struct pci_dev *pdev)
+{ return false; }
 #endif /* CONFIG_PCI_PRI */
 
 #ifdef CONFIG_PCI_PASID