[PATCH] SignedCapsulePkg: add PcdLowestSupportedFirmwareVersion

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

Add a PCD that holds the lowest supported version number, so that we
can allow the platform to configure this at build time.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
As discussed a while ago:
https://lists.01.org/pipermail/edk2-devel/2018-March/022914.html

 SignedCapsulePkg/SignedCapsulePkg.dec | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/SignedCapsulePkg/SignedCapsulePkg.dec b/SignedCapsulePkg/SignedCapsulePkg.dec
index b27e87409b19..f06e07656de9 100644
--- a/SignedCapsulePkg/SignedCapsulePkg.dec
+++ b/SignedCapsulePkg/SignedCapsulePkg.dec
@@ -52,6 +52,10 @@ [PcdsFixedAtBuild, PcdsPatchableInModule, PcdsDynamic, PcdsDynamicEx]
   # @Prompt GUID of the FFS which contains the Pkcs7TestPublicKeyFile.
   gEfiSignedCapsulePkgTokenSpaceGuid.PcdEdkiiPkcs7TestPublicKeyFileGuid|{0xba, 0xf5, 0x93, 0xf0, 0x37, 0x6f, 0x16, 0x48, 0x9e, 0x52, 0x91, 0xbe, 0xa0, 0xf7, 0xe0, 0xb8}|VOID*|0xA0010002
 
+  ## This is the lowest supported version number that can be upgraded to, as exposed via the System Firmware descriptor.
+  # @Prompt Lowest support version number that can be upgraded to via capsule update
+  gEfiSignedCapsulePkgTokenSpaceGuid.PcdLowestSupportedFirmwareVersion|0x1|UINT32|0xA0010003
+
 [PcdsDynamicEx]
   ## This dynamic PCD holds the EDKII system firmware image descriptor.
   #  This information can be used for version check in EDKII system FMP capsule.
-- 
2.17.0