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

From: Julia Suvorova
Subject: [PATCH 4/5] hw/i386/acpi-build: Deny control on PCIe Native Hot-plug in _OSC
Date: Wed, 10 Nov 2021 06:30:13 +0100

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

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>
 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..a2f92ab32b 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 acpi_pcihp)
     Aml *if_ctx;
     Aml *if_ctx2;
@@ -1345,6 +1345,7 @@ static Aml *build_q35_osc_method(void)
     Aml *method;
     Aml *a_cwd1 = aml_name("CDW1");
     Aml *a_ctrl = aml_local(0);
+    const uint64_t hotplug = acpi_pcihp ? 0x1E : 0x1F;
     method = aml_method("_OSC", 4, AML_NOTSERIALIZED);
     aml_append(method, aml_create_dword_field(aml_arg(3), aml_int(0), "CDW1"));
@@ -1359,8 +1360,9 @@ 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(hotplug), 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(false));
             } else {
                 aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0A03")));

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