Currently the bit 0 of the flags field of Root Port ATS capability reporting
structure sub-table under the DMAR table is set to 1. This indicates ALL_PORTS,
thus enabling ATS capability for all pcie roots without the ability to turn off
ATS for some ports and leaving ATS on for others.

This change clears the bit 0 of the flags field of the above structure and
explicitly adds scopes for every pcie root port in the structure so that ATS
is enabled for all of them. In future, we might add new attribite to the root
ports so that we can selectively enable ATS for some and leave ATS off for
others.

Signed-off-by: Ani Sinha <ani@anisinha.ca>
---
 hw/i386/acpi-build.c | 74 ++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 72 insertions(+), 2 deletions(-)

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index 0355bd3dda..9c5a555536 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -60,6 +60,7 @@
 #include "hw/i386/fw_cfg.h"
 #include "hw/i386/ich9.h"
 #include "hw/pci/pci_bus.h"
+#include "hw/pci/pcie_port.h"
 #include "hw/pci-host/q35.h"
 #include "hw/i386/x86-iommu.h"
 
@@ -2118,6 +2119,60 @@ dmar_host_bridges(Object *obj, void *opaque)
     return 0;
 }
 
+/*
+ * Insert DMAR scope for PCIE root ports
+ */
+static void
+insert_pcie_root_port_scope(PCIBus *bus, PCIDevice *dev, void *opaque)
+{
+    const size_t device_scope_size = 6 + 2;
+                                   /* device scope structure + 1 path entry */
+    GArray *scope_blob = opaque;
+
+    /*
+     * We are only interested in PCIE root ports. We can extend
+     * this to check for specific properties of PCIE root ports and based
+     * on that remove some ports from having ATS capability.
+     */
+    if (!object_dynamic_cast(OBJECT(dev), TYPE_PCIE_ROOT_PORT)) {
+        return;
+    }
+
+    /* Dmar Scope Type: 0x02 for all PCIE root ports */
+    build_append_int_noprefix(scope_blob, 0x02, 1);
+
+    /* length */
+    build_append_int_noprefix(scope_blob, device_scope_size, 1);
+    /* reserved */
+    build_append_int_noprefix(scope_blob, 0, 2);
+    /* enumeration_id */
+    build_append_int_noprefix(scope_blob, 0, 1);
+    /* bus */
+    build_append_int_noprefix(scope_blob, pci_bus_num(bus), 1);
+    /* device */
+    build_append_int_noprefix(scope_blob, PCI_SLOT(dev->devfn), 1);
+    /* function */
+    build_append_int_noprefix(scope_blob, PCI_FUNC(dev->devfn), 1);
+}
+
+/* For a given PCI host bridge, walk and insert DMAR scope */
+static int
+dmar_pcie_root_ports(Object *obj, void *opaque)
+{
+    GArray *scope_blob = opaque;
+
+    if (object_dynamic_cast(obj, TYPE_PCI_HOST_BRIDGE)) {
+        PCIBus *bus = PCI_HOST_BRIDGE(obj)->bus;
+
+        if (bus && !pci_bus_bypass_iommu(bus)) {
+            pci_for_each_device_under_bus(bus, insert_pcie_root_port_scope,
+                                          scope_blob);
+        }
+    }
+
+    return 0;
+}
+
 /*
  * Intel ® Virtualization Technology for Directed I/O
  * Architecture Specification. Revision 3.3
@@ -2190,11 +2245,26 @@ build_dmar_q35(GArray *table_data, BIOSLinker *linker, const char *oem_id,
 
     if (iommu->dt_supported) {
         /* 8.5 Root Port ATS Capability Reporting Structure */
+        /*
+         * A PCI bus walk, for each PCIE root port.
+         * Since we did not enable ALL_PORTS bit in the flags above, we
+         * need to add the scope for each pcie root port explicitly
+         * that are attached to bus0 with iommu enabled.
+         */
+        scope_blob = g_array_new(false, true, 1);
+        object_child_foreach_recursive(object_get_root(),
+                                       dmar_pcie_root_ports, scope_blob);
+
         build_append_int_noprefix(table_data, 2, 2); /* Type */
-        build_append_int_noprefix(table_data, 8, 2); /* Length */
-        build_append_int_noprefix(table_data, 1 /* ALL_PORTS */, 1); /* Flags */
+        build_append_int_noprefix(table_data,
+                                  8 + scope_blob->len, 2); /* Length */
+        build_append_int_noprefix(table_data, 0, 1); /* Flags */
         build_append_int_noprefix(table_data, 0, 1); /* Reserved */
         build_append_int_noprefix(table_data, 0, 2); /* Segment Number */
+
+        /* now add the scope to the sub-table */
+        g_array_append_vals(table_data, scope_blob->data, scope_blob->len);
+        g_array_free(scope_blob, true);
     }
 
     acpi_table_end(linker, &table);
-- 
2.25.1