Re: [edk2-devel] PCD Migration issue

["Liming Gao" <liming.gao@intel.com>]

Andrew:
  Current implementation requires PEI PcdDB and DXE PcdDB match. This is like a new request for PCD DataBase. It requests PCD DB binary format and Dynamic PCD token assignment be compatible in the different version.

Thanks
Liming
> -----Original Message-----
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Andrew Fish via Groups.Io
> Sent: Tuesday, February 11, 2020 1:39 AM
> To: devel@edk2.groups.io
> Subject: [edk2-devel] PCD Migration issue
> 
> We recently hit an issue when updating our UDK version in our common code base. Our recovery update path started failing for older
> platforms since the PEI was the old UDK version and the DXE from the Capsule was the new UDK version. Basically the version of the PCD
> changed. It looks like there are some checks, but the seem to be more about making sure the build systems matches the code vs. dealing
> with an update case like we hit.
> 
> It does not look like the PCD database is designed to deal with this. We are fixing this by extracting the PEI PCD database from the
> capsule and then having some platform specific code to patch any PCD entries that got set in PEI that are needed by DXE.
> 
> In the future it would be helpful if the PCD database would change in some what of a backward compatible way, and have the headers
> needed to parse the old and new version.
> 
> It also seems like adding a Dynamic PCD could potentially change the token layout and thus break compatibility? Is there any scheme to
> keep a previous token layout?
> 
> Thanks,
> 
> Andrew Fish
>