[Qemu-devel] [PATCH v2] pc: acpi: fix pvpanic for buggy guests

["Radim Krčmář" <rkrcmar@redhat.com>]

In the old times, we always had pvpanic in ACPI and a _STA method told
the guest not to use it.  Automatic generation dropped the _STA method
as the specification says that missing _STA means enabled and working.
Some guests (Linux) had buggy drivers and this change made them unable
to utilize pvpanic.

A Linux patch is posted as well, but I think it's worth to make pvpanic
useable on old guests at the price of three lines and few bytes of SSDT.

The old _STA method was
  Method (_STA, 0, NotSerialized) {
      Store (PEST, Local0)
      If (LEqual (Local0, Zero)) {
          Return (Zero) }
      Else {
          Return (0x0F) }}

Igor pointed out that we don't need to use a method to return a constant
and that 0xB (don't show in UI) is the common definition now.

Also, the device used to be PEVT.  (PEVT as in "panic event"?)

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
 v2: Use name_decl instead of method and return 0xb [Igor]
     Improve subject an commit message.
 
 Btw. I dislike the comment, so I've added a personal TODO to write 0xB
 in a programmer-friendly way.

 hw/i386/acpi-build.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index 73259e729b9f..50f4951ec79e 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -733,7 +733,7 @@ build_ssdt(GArray *table_data, GArray *linker,
     if (misc->pvpanic_port) {
         scope = aml_scope("\\_SB.PCI0.ISA");
 
-        dev = aml_device("PEVR");
+        dev = aml_device("PEVT");
         aml_append(dev, aml_name_decl("_HID", aml_string("QEMU0001")));
 
         crs = aml_resource_template();
@@ -748,6 +748,9 @@ build_ssdt(GArray *table_data, GArray *linker,
         aml_append(field, aml_named_field("PEPT", 8));
         aml_append(dev, field);
 
+        /* device present, functioning, decoding, not shown in UI */
+        aml_append(dev, aml_name_decl("_STA", aml_int(0xB)));
+
         method = aml_method("RDPT", 0);
         aml_append(method, aml_store(aml_name("PEPT"), aml_local(0)));
         aml_append(method, aml_return(aml_local(0)));
-- 
2.4.2