[PATCH v1] i440fx/acpi: don't hot-unplug cold plugged bridges when their hotplug switch is off

[Ani Sinha]

Cold plugged bridges should not be hot unpluggable, even when their hotplug 
property
(acpi-pci-hotplug-with-bridge-support) is turned off. However, with the current
implementaton, windows would try to hot-unplug a pci bridge when it's hotplug 
switch
is off. This is regardless of whether there are devices attached to the bridge. 
When
devices are attached to the bridge, the bridge is ultimately not 
hot-unpluggable. We
have a demo video here: https://youtu.be/pME2sjyQweo

In this fix, we identify a cold plugged bridge and for cold plugged bridges, we 
do not
add the appropriate amls and acpi methods that are used by the OS to identify a 
hot-
unpluggable pci device. After this change, Windows does not show an option to 
eject the
PCI bridge. A demo video is here:  https://youtu.be/kbgej5B9Hgs

While at it, I have also updated a stale comment.

This change is tested with a Windows 2012R2 guest image running on Ubuntu host. 
This
change is based off of upstream qemu master branch tag v5.1.0.

Signed-off-by: Ani Sinha <ani@anisinha.ca>
---
 hw/i386/acpi-build.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index b7bcbbbb2a..90b863f4ec 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -359,6 +359,7 @@ static void build_append_pci_bus_devices(Aml *parent_scope, 
PCIBus *bus,
         int slot = PCI_SLOT(i);
         bool hotplug_enabled_dev;
         bool bridge_in_acpi;
+        bool cold_plugged_bridge;
 
         if (!pdev) {
             if (bsel) { /* add hotplug slots for non present devices */
@@ -380,15 +381,14 @@ static void build_append_pci_bus_devices(Aml 
*parent_scope, PCIBus *bus,
         pc = PCI_DEVICE_GET_CLASS(pdev);
         dc = DEVICE_GET_CLASS(pdev);
 
-        /* When hotplug for bridges is enabled, bridges are
-         * described in ACPI separately (see build_pci_bus_end).
-         * In this case they aren't themselves hot-pluggable.
+        /*
+         * Cold plugged bridges aren't themselves hot-pluggable.
          * Hotplugged bridges *are* hot-pluggable.
          */
-        bridge_in_acpi = pc->is_bridge && pcihp_bridge_en &&
-            !DEVICE(pdev)->hotplugged;
+        cold_plugged_bridge = pc->is_bridge && !DEVICE(pdev)->hotplugged;
+        bridge_in_acpi =  cold_plugged_bridge && pcihp_bridge_en;
 
-        hotplug_enabled_dev = bsel && dc->hotpluggable && !bridge_in_acpi;
+        hotplug_enabled_dev = bsel && dc->hotpluggable && !cold_plugged_bridge;
 
         if (pc->class_id == PCI_CLASS_BRIDGE_ISA) {
             continue;
-- 
2.17.1