pcihp: acpi: ignore coldplugged bridges when composing hotpluggable slots

coldplugged bridges are not unpluggable, so there is no need
to describe slots where they are plugged as hotpluggable. To
that effect we have a condition that marks slot as non-hotpluggable
if it's populated by coldplugged bridge and prevents generation
_SUN/_EJ0 objects for it. That leaves dynamic _DSM method on
such slot (which also depends on BSEL and pcihp hardware).
This _DSM method provides only dynamic acpi-index support so far,
which is not actually used/supported by linux kernel for bridges
and it's doubtful there will be need for it at all.

So it's rather pointless to generate acpi-index related AML
for bridges and we can simplify hotplug slots generator a bit
more by completely ignoring coldplugged bridges on hotplug path.

Another point in favor of dropping dynamic _DSM support, is
that we can replace it with static _DSM if necessary since
a slot with bridge can't change during VM runtime and without
any dependency on ACPI PCI hotplug at that.
Later I plan to implement bridge specific static _DSM
   PCI Firmware Specification 3.2
   4.6.5.  _DSM for Ignoring PCI Boot Configurations
part of spec, to fix longstanding issue with fixed IO/MEM
resource assignment that often leads to hotplugged device
being in-operational within the guest due limited IO/MEM
windows programmed on bridge at boot time.

Expected change when coldplugged bridge is ignored by hotplug
code, should look like:
-            Scope (S18)
-            {
-                Name (ASUN, 0x03)
-                Method (_DSM, 4, Serialized)  // _DSM: Device-Specific Method
-                {
-                    Local0 = Package (0x02)
-                        {
-                            BSEL,
-                            ASUN
-                        }
-                    Return (PDSM (Arg0, Arg1, Arg2, Arg3, Local0))
-                }
-            }

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20230112140312.3096331-37-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 6 insertions, 10 deletions

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index 2077efb..a02608c 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -409,8 +409,11 @@ static bool is_devfn_ignored_generic(const int devfn, const PCIBus *bus)
 
 static bool is_devfn_ignored_hotplug(const int devfn, const PCIBus *bus)
 {
-    if (bus->devices[devfn]) {
-        return is_devfn_ignored_generic(devfn, bus);
+    PCIDevice *pdev = bus->devices[devfn];
+    if (pdev) {
+        return is_devfn_ignored_generic(devfn, bus) ||
+               /* Cold plugged bridges aren't themselves hot-pluggable */
+               (IS_PCI_BRIDGE(pdev) && !DEVICE(pdev)->hotplugged);
     } else { /* non populated slots */
          /*
          * hotplug is supported only for non-multifunction device
@@ -445,14 +448,7 @@ static void build_append_pcihp_slots(Aml *parent_scope, PCIBus *bus,
         }
 
         if (pdev) {
-            /*
-             * Cold plugged bridges aren't themselves hot-pluggable.
-             * Hotplugged bridges *are* hot-pluggable.
-             */
-            bool cold_plugged_bridge = IS_PCI_BRIDGE(pdev) &&
-                                  !DEVICE(pdev)->hotplugged;
-            hotpluggbale_slot = DEVICE_GET_CLASS(pdev)->hotpluggable &&
-                                !cold_plugged_bridge;
+            hotpluggbale_slot = DEVICE_GET_CLASS(pdev)->hotpluggable;
             dev = aml_scope("S%.02X", devfn);
         } else {
             dev = aml_device("S%.02X", devfn);