AMD/IOMMU: add helper to check whether ATS is to be used for a device

The same set of conditions is used in three places, requiring to be kept
in sync. Introduce a helper to centralize these checks.

To allow all parameters of the new helper be pointer-to-const,
iommu_has_cap() also needs its 1st parameter to be constified. Beyond
that further "modernize" that function.

Requested-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

xen/drivers/passthrough/amd/iommu.h

@@ -341,9 +341,9 @@ static inline void __free_amd_iommu_tables(void *table, unsigned int order)
     free_xenheap_pages(table, order);
 }
 
-static inline int iommu_has_cap(struct amd_iommu *iommu, uint32_t bit)
+static inline bool iommu_has_cap(const struct amd_iommu *iommu, unsigned int bit)
 {
-    return !!(iommu->cap.header & (1u << bit));
+    return iommu->cap.header & (1u << bit);
 }
 
 /* access device id field from iommu cmd */

xen/drivers/passthrough/amd/pci_amd_iommu.c

@@ -114,6 +114,16 @@ static bool any_pdev_behind_iommu(const struct domain *d,
     return false;
 }
 
+static bool use_ats(
+    const struct pci_dev *pdev,
+    const struct amd_iommu *iommu,
+    const struct ivrs_mappings *ivrs_dev)
+{
+    return !ivrs_dev->block_ats &&
+           iommu_has_cap(iommu, PCI_CAP_IOTLB_SHIFT) &&
+           pci_ats_device(iommu->seg, pdev->bus, pdev->devfn);
+}
+
 static int __must_check amd_iommu_setup_domain_device(
     struct domain *domain, struct amd_iommu *iommu,
     uint8_t devfn, struct pci_dev *pdev)
@@ -185,9 +195,7 @@ static int __must_check amd_iommu_setup_domain_device(
         dte->ex = ivrs_dev->dte_allow_exclusion;
         dte->sys_mgt = MASK_EXTR(ivrs_dev->device_flags, ACPI_IVHD_SYSTEM_MGMT);
 
-        if ( pci_ats_device(iommu->seg, bus, pdev->devfn) &&
-             !ivrs_dev->block_ats &&
-             iommu_has_cap(iommu, PCI_CAP_IOTLB_SHIFT) )
+        if ( use_ats(pdev, iommu, ivrs_dev) )
             dte->i = ats_enabled;
 
         spin_unlock_irqrestore(&iommu->lock, flags);
@@ -248,9 +256,7 @@ static int __must_check amd_iommu_setup_domain_device(
         ASSERT(dte->sys_mgt == MASK_EXTR(ivrs_dev->device_flags,
                                          ACPI_IVHD_SYSTEM_MGMT));
 
-        if ( pci_ats_device(iommu->seg, bus, pdev->devfn) &&
-             !ivrs_dev->block_ats &&
-             iommu_has_cap(iommu, PCI_CAP_IOTLB_SHIFT) )
+        if ( use_ats(pdev, iommu, ivrs_dev) )
             ASSERT(dte->i == ats_enabled);
 
         spin_unlock_irqrestore(&iommu->lock, flags);
@@ -268,9 +274,7 @@ static int __must_check amd_iommu_setup_domain_device(
 
     ASSERT(pcidevs_locked());
 
-    if ( pci_ats_device(iommu->seg, bus, pdev->devfn) &&
-         !ivrs_dev->block_ats &&
-         iommu_has_cap(iommu, PCI_CAP_IOTLB_SHIFT) &&
+    if ( use_ats(pdev, iommu, ivrs_dev) &&
          !pci_ats_enabled(iommu->seg, bus, pdev->devfn) )
     {
         if ( devfn == pdev->devfn )