pcihp: make pci_read() mmio calback compatible with legacy ACPI hotplug

due to recent change introduced by:
"pcihp: reduce number of device check events"

'up' field is cleared right after it's read.
This is incompatible with legacy BIOS ACPI code
where PCNF ACPI method reads this field 32 times.

To make pci_read mmio callback compatible with legacy
'up' behavior, pcihp code will need to know in which
mode it runs add 'legacy_piix' field to AcpiPciHpState
structure and alter register behavior accordingly.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

2 files changed, 7 insertions, 3 deletions

diff --git a/hw/acpi/pcihp.c b/hw/acpi/pcihp.c
index 64c8cf2..974f01c 100644
--- a/hw/acpi/pcihp.c
+++ b/hw/acpi/pcihp.c
@@ -215,7 +215,9 @@ static uint64_t pci_read(void *opaque, hwaddr addr, unsigned int size)
     switch (addr) {
     case PCI_UP_BASE:
         val = s->acpi_pcihp_pci_status[bsel].up;
-        s->acpi_pcihp_pci_status[bsel].up = 0;
+        if (!s->legacy_piix) {
+            s->acpi_pcihp_pci_status[bsel].up = 0;
+        }
         ACPI_PCIHP_DPRINTF("pci_up_read %" PRIu32 "\n", val);
         break;
     case PCI_DOWN_BASE:
@@ -273,9 +275,10 @@ static const MemoryRegionOps acpi_pcihp_io_ops = {
 };
 
 void acpi_pcihp_init(AcpiPciHpState *s, PCIBus *root_bus,
-                     MemoryRegion *address_space_io)
+                     MemoryRegion *address_space_io, bool bridges_enabled)
 {
     s->root= root_bus;
+    s->legacy_piix = !bridges_enabled;
     memory_region_init_io(&s->io, NULL, &acpi_pcihp_io_ops, s,
                           "acpi-pci-hotplug",
                           PCI_HOTPLUG_SIZE);
diff --git a/hw/acpi/piix4.c b/hw/acpi/piix4.c
index 5d55a3c..2aedfe5 100644
--- a/hw/acpi/piix4.c
+++ b/hw/acpi/piix4.c
@@ -695,7 +695,8 @@ static void piix4_acpi_system_hot_add_init(MemoryRegion *parent,
     memory_region_add_subregion(parent, GPE_BASE, &s->io_gpe);
 
     if (s->use_acpi_pci_hotplug) {
-        acpi_pcihp_init(&s->acpi_pci_hotplug, bus, parent);
+        acpi_pcihp_init(&s->acpi_pci_hotplug, bus, parent,
+                        s->use_acpi_pci_hotplug);
     } else {
         memory_region_init_io(&s->io_pci, OBJECT(s), &piix4_pci_ops, s,
                               "acpi-pci-hotplug", PCI_HOTPLUG_SIZE);