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

[Ani Sinha]

Julia Michael,

Can you please provide your inputs on this one and the corresponding unit tests?

On Fri, Sep 4, 2020 at 9:40 PM Ani Sinha <ani@anisinha.ca> wrote:

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