hw/i386: declare ACPI mother board resource for MMCONFIG region

hw/i386: declare ACPI mother board resource for MMCONFIG region

Declare PNP0C01 device to reserve MMCONFIG region to conform to the
spec better and play nice with guest BIOSes/OSes.

According to PCI Firmware Specification[0], MMCONFIG region must be
reserved by declaring a motherboard resource. It's optional to reserve
the region in memory map by Int 15 E820h or EFIGetMemoryMap.
Guest Linux checks if the MMCFG region is reserved by bios memory map
or ACPI resource. If it's not reserved, Linux falls back to legacy PCI
configuration access.

TDVF [1] [2] doesn't reserve MMCONFIG the region in memory map.
On the other hand OVMF reserves it in memory map without declaring a
motherboard resource. With memory map reservation, linux guest uses
MMCONFIG region. However it doesn't comply to PCI Firmware
specification.

[0] PCI Firmware specification Revision 3.2
  4.1.2 MCFG Table Description table 4-2 NOTE 2
  If the operating system does not natively comprehend reserving the
  MMCFG region, The MMCFG region must e reserved by firmware. ...
  For most systems, the mortheroard resource would appear at the root
  of the ACPI namespace (under \_SB)...
  The resource can optionally be returned in Int15 E820h or
  EFIGetMemoryMap as reserved memory but must always be reported
  through ACPI as a motherboard resource

[1] TDX: Intel Trust Domain Extension
    https://software.intel.com/content/www/us/en/develop/articles/intel-trust-domain-extensions.html
[2] TDX Virtual Firmware
    https://github.com/tianocore/edk2-staging/tree/TDVF

The change to DSDT is as follows.
@@ -68,32 +68,47 @@

                     If ((CDW3 != Local0))
                     {
                         CDW1 |= 0x10
                     }

                     CDW3 = Local0
                 }
                 Else
                 {
                     CDW1 |= 0x04
                 }

                 Return (Arg3)
             }
         }
+
+        Device (DRAC)
+        {
+            Name (_HID, "PNP0C01" /* System Board */)  // _HID: Hardware ID
+            Name (_CRS, ResourceTemplate ()  // _CRS: Current Resource Settings
+            {
+                DWordMemory (ResourceProducer, PosDecode, MinFixed, MaxFixed, NonCacheable, ReadWrite,
+                    0x00000000,         // Granularity
+                    0xB0000000,         // Range Minimum
+                    0xBFFFFFFF,         // Range Maximum
+                    0x00000000,         // Translation Offset
+                    0x10000000,         // Length
+                    ,, , AddressRangeMemory, TypeStatic)
+            })
+        }
     }

     Scope (_SB)
     {
         Device (HPET)
         {
             Name (_HID, EisaId ("PNP0103") /* HPET System Timer */)  // _HID: Hardware ID
             Name (_UID, Zero)  // _UID: Unique ID
             OperationRegion (HPTM, SystemMemory, 0xFED00000, 0x0400)
             Field (HPTM, DWordAcc, Lock, Preserve)
             {
                 VEND,   32,
                 PRD,    32
             }

             Method (_STA, 0, NotSerialized)  // _STA: Status

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Message-Id: <6f686b45ce7bc43048c56dbb46e72e1fe51927e6.1613615732.git.isaku.yamahata@intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>