OvmfPkg: SmbiosPlatformDxe: eliminate duplicate entry point validation

At this point all platforms that use OvmfPkg/SmbiosPlatformDxe in edk2,
namely ArmVirtQemu.dsc and OvmfPkg*.dsc, have been migrated to
SmbiosVersionLib. Therefore SmbiosPlatformDxe itself can forego verifying
QEMU's SMBIOS entry point; if SmbiosVersionLib's validation was
successful, it should just rely on that.

(Note that SmbiosPlatformDxe has a depex on EFI_SMBIOS_PROTOCOL, installed
by SmbiosDxe, containing SmbiosVersionLib, therefore the set/get order of
PcdQemuSmbiosValidated is ensured.)

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Wei Huang <wei@redhat.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Gabriel L. Somlo <somlo@cmu.edu>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18180 6f19259b-4bc3-4df7-8a09-765794883524

OvmfPkg/Library/SmbiosVersionLib/DetectSmbiosVersionLib.c

@@ -40,6 +40,15 @@ DetectSmbiosVersion (
   QEMU_SMBIOS_ANCHOR   QemuAnchor;
   UINT16               SmbiosVersion;
 
+  if (PcdGetBool (PcdQemuSmbiosValidated)) {
+    //
+    // Some other module, linked against this library, has already performed
+    // the task at hand. This should never happen, but it's easy to handle;
+    // just exit early.
+    //
+    return RETURN_SUCCESS;
+  }
+
   if (RETURN_ERROR (QemuFwCfgFindFile (
                       "etc/smbios/smbios-anchor", &Anchor, &AnchorSize)) ||
       RETURN_ERROR (QemuFwCfgFindFile (
@@ -72,5 +81,10 @@ DetectSmbiosVersion (
     SmbiosVersion));
   PcdSet16 (PcdSmbiosVersion, SmbiosVersion);
 
+  //
+  // SMBIOS platform drivers can now fetch and install
+  // "etc/smbios/smbios-tables" from QEMU.
+  //
+  PcdSetBool (PcdQemuSmbiosValidated, TRUE);
   return RETURN_SUCCESS;
 }