OvmfPkg: introduce PcdCsmEnable feature flag

In the DXE phase and later, it is possible for a module to dynamically
determine whether a CSM is enabled. An example can be seen in commit
855743f ("OvmfPkg: prevent 64-bit MMIO BAR degradation if there is no
CSM", 2016-05-25).

SEC and PEI phase modules cannot check the Legacy BIOS Protocol however.
For their sake, introduce a new feature PCD that simply reflects the
CSM_ENABLE build flag.

Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Julien Grall <julien@xen.org>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1512
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20200129214412.2361-11-lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

OvmfPkg/OvmfPkg.dec

@@ -276,3 +276,8 @@
   #  runtime OS from tampering with firmware structures (special memory ranges
   #  used by OVMF, the varstore pflash chip, LockBox etc).
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire|FALSE|BOOLEAN|0x1e
+
+  ## Informs modules (including pre-DXE-phase modules) whether the platform
+  #  firmware contains a CSM (Compatibility Support Module).
+  #
+  gUefiOvmfPkgTokenSpaceGuid.PcdCsmEnable|FALSE|BOOLEAN|0x35

OvmfPkg/OvmfPkgIa32.dsc

@@ -428,6 +428,9 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutGopSupport|TRUE
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutUgaSupport|FALSE
   gEfiMdeModulePkgTokenSpaceGuid.PcdInstallAcpiSdtProtocol|TRUE
+!ifdef $(CSM_ENABLE)
+  gUefiOvmfPkgTokenSpaceGuid.PcdCsmEnable|TRUE
+!endif
 !if $(SMM_REQUIRE) == TRUE
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire|TRUE
   gUefiCpuPkgTokenSpaceGuid.PcdCpuSmmEnableBspElection|FALSE

OvmfPkg/OvmfPkgIa32X64.dsc

@@ -433,6 +433,9 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutGopSupport|TRUE
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutUgaSupport|FALSE
   gEfiMdeModulePkgTokenSpaceGuid.PcdInstallAcpiSdtProtocol|TRUE
+!ifdef $(CSM_ENABLE)
+  gUefiOvmfPkgTokenSpaceGuid.PcdCsmEnable|TRUE
+!endif
 !if $(SMM_REQUIRE) == TRUE
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire|TRUE
   gUefiCpuPkgTokenSpaceGuid.PcdCpuSmmEnableBspElection|FALSE

OvmfPkg/OvmfPkgX64.dsc

@@ -433,6 +433,9 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutGopSupport|TRUE
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutUgaSupport|FALSE
   gEfiMdeModulePkgTokenSpaceGuid.PcdInstallAcpiSdtProtocol|TRUE
+!ifdef $(CSM_ENABLE)
+  gUefiOvmfPkgTokenSpaceGuid.PcdCsmEnable|TRUE
+!endif
 !if $(SMM_REQUIRE) == TRUE
   gUefiOvmfPkgTokenSpaceGuid.PcdSmmSmramRequire|TRUE
   gUefiCpuPkgTokenSpaceGuid.PcdCpuSmmEnableBspElection|FALSE

OvmfPkg/OvmfXen.dsc

@@ -361,6 +361,9 @@
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutGopSupport|TRUE
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutUgaSupport|FALSE
   gEfiMdeModulePkgTokenSpaceGuid.PcdInstallAcpiSdtProtocol|TRUE
+!ifdef $(CSM_ENABLE)
+  gUefiOvmfPkgTokenSpaceGuid.PcdCsmEnable|TRUE
+!endif
 
 [PcdsFixedAtBuild]
   gEfiMdeModulePkgTokenSpaceGuid.PcdStatusCodeMemorySize|1