pcie_root_port: Allow ACS to be disabled

ACS was added in 4.0 unconditionally, this breaks migration
compatibility.
Allow ACS to be disabled by adding a property that's
checked by pcie_root_port.

Unfortunately pcie-root-port doesn't have any instance data,
so there's no where for that flag to live, so stuff it into
PCIESlot.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20190730093719.12958-2-dgilbert@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/pci-bridge/pcie_root_port.c

@@ -111,7 +111,7 @@ static void rp_realize(PCIDevice *d, Error **errp)
     pcie_aer_root_init(d);
     rp_aer_vector_update(d);
 
-    if (rpc->acs_offset) {
+    if (rpc->acs_offset && !s->disable_acs) {
         pcie_acs_init(d, rpc->acs_offset);
     }
     return;
@@ -145,6 +145,7 @@ static void rp_exit(PCIDevice *d)
 static Property rp_props[] = {
     DEFINE_PROP_BIT(COMPAT_PROP_PCP, PCIDevice, cap_present,
                     QEMU_PCIE_SLTCAP_PCP_BITNR, true),
+    DEFINE_PROP_BOOL("disable-acs", PCIESlot, disable_acs, false),
     DEFINE_PROP_END_OF_LIST()
 };
 

include/hw/pci/pcie_port.h

@@ -53,6 +53,8 @@ struct PCIESlot {
     PCIExpLinkSpeed speed;
     PCIExpLinkWidth width;
 
+    /* Disable ACS (really for a pcie_root_port) */
+    bool        disable_acs;
     QLIST_ENTRY(PCIESlot) next;
 };