[PATCH v3] i440fx/acpi: do not add hotplug related amls for cold plugged bridges

[Ani Sinha <ani@anisinha.ca>]

Cold plugged bridges are not hot unpluggable, even when their hotplug
property (acpi-pci-hotplug-with-bridge-support) is turned off. Please see
the function acpi_pcihp_pc_no_hotplug() (thanks Julia). 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. This is because we add amls like _EJ0 etc for the
pci slot where the bridge is cold plugged. 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-pluggable/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 and Windows 2019 server
guest image running on Ubuntu 18.04 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(-)

changelog:
v3: commit log updates providing more accurate information as received from Julia.
v2: cosmetic commit log updates with patch testing information.
v1: initial patch.


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