OvmfPkg/Tcg2ConfigPei: introduce a signalling PPI to depex on

On ARM systems, the TPM does not live at a fixed address, and so we
need the platform to discover it first. So introduce a PPI that signals
that the TPM address has been discovered and recorded in the appropriate
PCD, and make Tcg2ConfigPei depex on it when built for ARM or AARCH64.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2560
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>

OvmfPkg/OvmfPkg.dec

@@ -87,6 +87,11 @@
   gEfiLegacyBiosGuid                  = {0x2E3044AC, 0x879F, 0x490F, {0x97, 0x60, 0xBB, 0xDF, 0xAF, 0x69, 0x5F, 0x50}}
   gEfiLegacyDevOrderVariableGuid      = {0xa56074db, 0x65fe, 0x45f7, {0xbd, 0x21, 0x2d, 0x2b, 0xdd, 0x8e, 0x96, 0x52}}
 
+[Ppis]
+  # PPI whose presence in the PPI database signals that the TPM base address
+  # has been discovered and recorded
+  gOvmfTpmDiscoveredPpiGuid           = {0xb9a61ad0, 0x2802, 0x41f3, {0xb5, 0x13, 0x96, 0x51, 0xce, 0x6b, 0xd5, 0x75}}
+
 [Protocols]
   gVirtioDeviceProtocolGuid           = {0xfa920010, 0x6785, 0x4941, {0xb6, 0xec, 0x49, 0x8c, 0x57, 0x9f, 0x16, 0x0a}}
   gXenBusProtocolGuid                 = {0x3d3ca290, 0xb9a5, 0x11e3, {0xb7, 0x5d, 0xb8, 0xac, 0x6f, 0x7d, 0x65, 0xe6}}

OvmfPkg/Tcg/Tcg2Config/Tcg2ConfigPei.inf

@@ -25,6 +25,7 @@
 [Packages]
   MdePkg/MdePkg.dec
   MdeModulePkg/MdeModulePkg.dec
+  OvmfPkg/OvmfPkg.dec
   SecurityPkg/SecurityPkg.dec
 
 [LibraryClasses]
@@ -43,5 +44,8 @@
 [Pcd]
   gEfiSecurityPkgTokenSpaceGuid.PcdTpmInstanceGuid                 ## PRODUCES
 
-[Depex]
+[Depex.IA32, Depex.X64]
   TRUE
+
+[Depex.ARM, Depex.AARCH64]
+  gOvmfTpmDiscoveredPpiGuid