pci: acpi hotplug: rename x-native-hotplug to x-do-not-expose-native-hotplug-cap

When ACPI PCI hotplug for Q35 was introduced (6.1), it was implemented
by hiding HPC capability on PCIE slot. That however led to a number of
regressions and to fix it, it was decided to keep HPC cap exposed
in ACPI PCI hotplug case and force guest in ACPI PCI hotplug mode
by other means [1].

That reduced meaning of x-native-hotplug to a compat knob [2] for
broken 6.1 machine type.
Rename property to match its current purpose.

1) 211afe5c69 (hw/i386/acpi-build: Deny control on PCIe Native Hot-plug in _OSC)
2) c318bef762 (hw/acpi/ich9: Add compat prop to keep HPC bit set for 6.1 machine type)

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20230112140312.3096331-10-imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

5 files changed, 16 insertions, 8 deletions

diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index 83c57c6..66cd718 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -257,8 +257,9 @@ static void pc_q35_init(MachineState *machine)
                                                  NULL);
 
     if (!keep_pci_slot_hpc && acpi_pcihp) {
-        object_register_sugar_prop(TYPE_PCIE_SLOT, "x-native-hotplug",
-                                   "false", true);
+        object_register_sugar_prop(TYPE_PCIE_SLOT,
+                                   "x-do-not-expose-native-hotplug-cap",
+                                   "true", true);
     }
 
     /* irq lines */
diff --git a/hw/pci-bridge/gen_pcie_root_port.c b/hw/pci-bridge/gen_pcie_root_port.c
index 20099a8..1ce4e7b 100644
--- a/hw/pci-bridge/gen_pcie_root_port.c
+++ b/hw/pci-bridge/gen_pcie_root_port.c
@@ -87,7 +87,12 @@ static void gen_rp_realize(DeviceState *dev, Error **errp)
         return;
     }
 
-    if (grp->res_reserve.io == -1 && s->hotplug && !s->native_hotplug) {
+    /*
+     * reserving IO space led to worse issues in 6.1, when this hunk was
+     * introduced. (see commit: 211afe5c69b59). Keep this broken for 6.1
+     * machine type ABI compatibility only
+     */
+    if (s->hide_native_hotplug_cap && grp->res_reserve.io == -1 && s->hotplug) {
         grp->res_reserve.io = GEN_PCIE_ROOT_DEFAULT_IO_RANGE;
     }
     int rc = pci_bridge_qemu_reserve_cap_init(d, 0,
diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
index 68a62da..924fdabd 100644
--- a/hw/pci/pcie.c
+++ b/hw/pci/pcie.c
@@ -611,11 +611,11 @@ void pcie_cap_slot_init(PCIDevice *dev, PCIESlot *s)
                                PCI_EXP_SLTCAP_ABP);
 
     /*
-     * Enable native hot-plug on all hot-plugged bridges unless
-     * hot-plug is disabled on the slot.
+     * Expose native hot-plug on all bridges if hot-plug is enabled on the slot.
+     * (unless broken 6.1 ABI is enforced for compat reasons)
      */
     if (s->hotplug &&
-        (s->native_hotplug || DEVICE(dev)->hotplugged)) {
+        (!s->hide_native_hotplug_cap || DEVICE(dev)->hotplugged)) {
         pci_long_test_and_set_mask(dev->config + pos + PCI_EXP_SLTCAP,
                                    PCI_EXP_SLTCAP_HPS |
                                    PCI_EXP_SLTCAP_HPC);
diff --git a/hw/pci/pcie_port.c b/hw/pci/pcie_port.c
index 687e4e7..65a397a 100644
--- a/hw/pci/pcie_port.c
+++ b/hw/pci/pcie_port.c
@@ -173,7 +173,8 @@ static Property pcie_slot_props[] = {
     DEFINE_PROP_UINT8("chassis", PCIESlot, chassis, 0),
     DEFINE_PROP_UINT16("slot", PCIESlot, slot, 0),
     DEFINE_PROP_BOOL("hotplug", PCIESlot, hotplug, true),
-    DEFINE_PROP_BOOL("x-native-hotplug", PCIESlot, native_hotplug, true),
+    DEFINE_PROP_BOOL("x-do-not-expose-native-hotplug-cap", PCIESlot,
+                     hide_native_hotplug_cap, false),
     DEFINE_PROP_END_OF_LIST()
 };
 
diff --git a/include/hw/pci/pcie_port.h b/include/hw/pci/pcie_port.h
index fd484af..6c40e37 100644
--- a/include/hw/pci/pcie_port.h
+++ b/include/hw/pci/pcie_port.h
@@ -63,7 +63,8 @@ struct PCIESlot {
     /* Indicates whether any type of hot-plug is allowed on the slot */
     bool        hotplug;
 
-    bool        native_hotplug;
+    /* broken ACPI hotplug compat knob to preserve 6.1 ABI intact */
+    bool        hide_native_hotplug_cap;
 
     QLIST_ENTRY(PCIESlot) next;
 };