[PATCH v2 5/9] i440fx/acpi: do not add hotplug related amls for cold plugged bridges

[Ani Sinha]

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

As a result of the patch, the following are the changes to the DSDT ACPI table:

@@ -858,38 +858,33 @@
                     Return (Zero)
                 }

                 Method (_S2D, 0, NotSerialized)  // _S2D: S2 Device State
                 {
                     Return (Zero)
                 }

                 Method (_S3D, 0, NotSerialized)  // _S3D: S3 Device State
                 {
                     Return (Zero)
                 }
             }

             Device (S18)
             {
-                Name (_SUN, 0x03)  // _SUN: Slot User Number
                 Name (_ADR, 0x00030000)  // _ADR: Address
-                Method (_EJ0, 1, NotSerialized)  // _EJx: Eject Device
-                {
-                    PCEJ (BSEL, _SUN)
-                }
             }

             Device (S20)
             {
                 Name (_SUN, 0x04)  // _SUN: Slot User Number
                 Name (_ADR, 0x00040000)  // _ADR: Address
                 Method (_EJ0, 1, NotSerialized)  // _EJx: Eject Device
                 {
                     PCEJ (BSEL, _SUN)
                 }
             }

             Device (S28)
             {
                 Name (_SUN, 0x05)  // _SUN: Slot User Number
                 Name (_ADR, 0x00050000)  // _ADR: Address
@@ -1148,37 +1143,32 @@
                     PCEJ (BSEL, _SUN)
                 }
             }

             Device (SF8)
             {
                 Name (_SUN, 0x1F)  // _SUN: Slot User Number
                 Name (_ADR, 0x001F0000)  // _ADR: Address
                 Method (_EJ0, 1, NotSerialized)  // _EJx: Eject Device
                 {
                     PCEJ (BSEL, _SUN)
                 }
             }

             Method (DVNT, 2, NotSerialized)
             {
-                If ((Arg0 & 0x08))
-                {
-                    Notify (S18, Arg1)
-                }
-
                 If ((Arg0 & 0x10))
                 {
                     Notify (S20, Arg1)
                 }

                 If ((Arg0 & 0x20))
                 {
                     Notify (S28, Arg1)
                 }

                 If ((Arg0 & 0x40))
                 {
                     Notify (S30, Arg1)
                 }

                 If ((Arg0 & 0x80))

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(-)

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index 7a5a8b3521..e079b686f5 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