pcihp: do not put empty PCNT in DSDT

count number of PCNT methods that actually call Notify
and if there aren't any, drop PCNT altogether.
It mostly affects 'Q35' tests where there is no root-ports
/bridges attached and 'PC' machine when ACPI PCI hotplug is
completely disabled.

Expected ASL change:

-            Method (PCNT, 0, NotSerialized)
-            {
-            }
...
         Method (_E01, 0, NotSerialized)  // _Exx: Edge-Triggered GPE
         {
-            Acquire (\_SB.PCI0.BLCK, 0xFFFF)
-            \_SB.PCI0.PCNT ()
-            Release (\_SB.PCI0.BLCK)
         }

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20230112140312.3096331-23-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 18 insertions, 8 deletions

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index d434ad9189..6368fcefa3 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -496,12 +496,13 @@ static void build_append_pci_bus_devices(Aml *parent_scope, PCIBus *bus,
     qobject_unref(bsel);
 }
 
-static void build_append_notfication_callback(Aml *parent_scope,
+static bool build_append_notfication_callback(Aml *parent_scope,
                                               const PCIBus *bus)
 {
     Aml *method;
     PCIBus *sec;
     QObject *bsel;
+    int nr_notifiers = 0;
 
     QLIST_FOREACH(sec, &bus->child, sibling) {
         Aml *br_scope = aml_scope("S%.02X", sec->parent_dev->devfn);
@@ -509,7 +510,8 @@ static void build_append_notfication_callback(Aml *parent_scope,
             !object_property_find(OBJECT(sec), ACPI_PCIHP_PROP_BSEL)) {
             continue;
         }
-        build_append_notfication_callback(br_scope, sec);
+        nr_notifiers = nr_notifiers +
+                       build_append_notfication_callback(br_scope, sec);
         aml_append(parent_scope, br_scope);
     }
 
@@ -530,6 +532,7 @@ static void build_append_notfication_callback(Aml *parent_scope,
                                      aml_int(1))); /* Device Check */
         aml_append(method, aml_call2("DVNT", aml_name("PCID"),
                                      aml_int(3))); /* Eject Request */
+        nr_notifiers++;
     }
 
     /* Notify about child bus events in any case */
@@ -544,6 +547,7 @@ static void build_append_notfication_callback(Aml *parent_scope,
 
     aml_append(parent_scope, method);
     qobject_unref(bsel);
+    return !!nr_notifiers;
 }
 
 static Aml *aml_pci_pdsm(void)
@@ -1742,20 +1746,26 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
     aml_append(dsdt, sb_scope);
 
     if (pm->pcihp_bridge_en || pm->pcihp_root_en) {
+        bool has_pcnt;
+
         Object *pci_host = acpi_get_i386_pci_host();
         PCIBus *bus = PCI_HOST_BRIDGE(pci_host)->bus;
 
         scope = aml_scope("\\_SB.PCI0");
-        build_append_notfication_callback(scope, bus);
-        aml_append(dsdt, scope);
+        has_pcnt = build_append_notfication_callback(scope, bus);
+        if (has_pcnt) {
+            aml_append(dsdt, scope);
+        }
 
         scope =  aml_scope("_GPE");
         {
             method = aml_method("_E01", 0, AML_NOTSERIALIZED);
-            aml_append(method,
-                aml_acquire(aml_name("\\_SB.PCI0.BLCK"), 0xFFFF));
-            aml_append(method, aml_call0("\\_SB.PCI0.PCNT"));
-            aml_append(method, aml_release(aml_name("\\_SB.PCI0.BLCK")));
+            if (has_pcnt) {
+                aml_append(method,
+                    aml_acquire(aml_name("\\_SB.PCI0.BLCK"), 0xFFFF));
+                aml_append(method, aml_call0("\\_SB.PCI0.PCNT"));
+                aml_append(method, aml_release(aml_name("\\_SB.PCI0.BLCK")));
+            }
             aml_append(scope, method);
         }
         aml_append(dsdt, scope);