[PATCH for 6.2 v2 4/5] hw/i386/acpi-build: Deny control on PCIe Native Hot-plug in _OSC

[Igor Mammedov <imammedo@redhat.com>]

From: Julia Suvorova <jusual@redhat.com>

There are two ways to enable ACPI PCI Hot-plug:

        * Disable the Hot-plug Capable bit on PCIe slots.

This was the first approach which led to regression [1-2], as
I/O space for a port is allocated only when it is hot-pluggable,
which is determined by HPC bit.

        * Leave the HPC bit on and disable PCIe Native Hot-plug in _OSC
          method.

This removes the (future) ability of hot-plugging switches with PCIe
Native hotplug since ACPI PCI Hot-plug only works with cold-plugged
bridges. If the user wants to explicitely use this feature, they can
disable ACPI PCI Hot-plug with:
        --global ICH9-LPC.acpi-pci-hotplug-with-bridge-support=off

Change the bit in _OSC method so that the OS selects ACPI PCI Hot-plug
instead of PCIe Native.

[1] https://gitlab.com/qemu-project/qemu/-/issues/641
[2] https://bugzilla.redhat.com/show_bug.cgi?id=2006409

Signed-off-by: Julia Suvorova <jusual@redhat.com>
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
v2:
  - (mst)
      * drop local hotplug var and opencode it
      * rename acpi_pcihp parameter to enable_native_pcie_hotplug
        to reflect what it actually does

tested:
  with hotplugging nic into 1 root port with seabios/ovmf/Fedora34
  Windows tested only with seabios (using exiting images)
  (installer fails to install regardless on bios)
---
 hw/i386/acpi-build.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index a3ad6abd33..a99c6e4fe3 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -1337,7 +1337,7 @@ static void build_x86_acpi_pci_hotplug(Aml *table, uint64_t pcihp_addr)
     aml_append(table, scope);
 }
 
-static Aml *build_q35_osc_method(void)
+static Aml *build_q35_osc_method(bool enable_native_pcie_hotplug)
 {
     Aml *if_ctx;
     Aml *if_ctx2;
@@ -1359,8 +1359,10 @@ static Aml *build_q35_osc_method(void)
     /*
      * Always allow native PME, AER (no dependencies)
      * Allow SHPC (PCI bridges can have SHPC controller)
+     * Disable PCIe Native Hot-plug if ACPI PCI Hot-plug is enabled.
      */
-    aml_append(if_ctx, aml_and(a_ctrl, aml_int(0x1F), a_ctrl));
+    aml_append(if_ctx, aml_and(a_ctrl,
+        aml_int(0x1E | (enable_native_pcie_hotplug ? 0x1 : 0x0)), a_ctrl));
 
     if_ctx2 = aml_if(aml_lnot(aml_equal(aml_arg(1), aml_int(1))));
     /* Unknown revision */
@@ -1449,7 +1451,7 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
         aml_append(dev, aml_name_decl("_CID", aml_eisaid("PNP0A03")));
         aml_append(dev, aml_name_decl("_ADR", aml_int(0)));
         aml_append(dev, aml_name_decl("_UID", aml_int(pcmc->pci_root_uid)));
-        aml_append(dev, build_q35_osc_method());
+        aml_append(dev, build_q35_osc_method(!pm->pcihp_bridge_en));
         aml_append(sb_scope, dev);
         if (mcfg_valid) {
             aml_append(sb_scope, build_q35_dram_controller(&mcfg));
@@ -1565,7 +1567,9 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
             if (pci_bus_is_express(bus)) {
                 aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0A08")));
                 aml_append(dev, aml_name_decl("_CID", aml_eisaid("PNP0A03")));
-                aml_append(dev, build_q35_osc_method());
+
+                /* Expander bridges do not have ACPI PCI Hot-plug enabled */
+                aml_append(dev, build_q35_osc_method(true));
             } else {
                 aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0A03")));
             }
-- 
2.27.0