acpi/core: always set SCI_EN when SMM isn't supported

If SMM is not supported, ACPI fixed hardware doesn't support
legacy-mode. ACPI-only platform. Where SCI_EN in PM1_CNT register is
always set.
The bit tells OS legacy mode(SCI_EN cleared) or ACPI mode(SCI_EN set).

With the next patch (setting fadt.smi_cmd = 0 when smm isn't enabled),
guest Linux tries to switch to ACPI mode, finds smi_cmd = 0, and then
fails to initialize acpi subsystem. This patch proactively fixes it.

This patch changes guest ABI. To keep compatibility, use
"smm-compat" introduced by earlier patch. If the property is true,
disable new behavior.

ACPI spec 4.8.10.1 PM1 Event Grouping
PM1 Eanble Registers
> For ACPI-only platforms (where SCI_EN is always set)

Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Message-Id: <500f62081626997e46f96377393d3662211763a8.1613615732.git.isaku.yamahata@intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/hw/core/machine.c b/hw/core/machine.c
index 970046f438..4386f57b5c 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -36,7 +36,10 @@
 #include "hw/virtio/virtio.h"
 #include "hw/virtio/virtio-pci.h"
 
-GlobalProperty hw_compat_5_2[] = {};
+GlobalProperty hw_compat_5_2[] = {
+    { "ICH9-LPC", "smm-compat", "on"},
+    { "PIIX4_PM", "smm-compat", "on"},
+};
 const size_t hw_compat_5_2_len = G_N_ELEMENTS(hw_compat_5_2);
 
 GlobalProperty hw_compat_5_1[] = {