Re: [RFC] PCD: Extended SKU support 1 - inheritance

["Kinney, Michael D" <michael.d.kinney@intel.com>]

Tim,

Can you please provide more details on your specific concerns along with some use cases?

This RFC does not change the SKU feature in EDK II.  This RFC simply provides a more 
efficient way for a developer to provide PCD values for different SKUs with fewer PCD
statements in a DSC file.

Today, every SKU is a based on the DEFAULT SKU and if a PCD requires a different value
than the DEFAULT SKU value, then a SKU specific PCD statement is required. 

With this proposal, a relationship between SKUs can be declared in the DSC file, so
SKUs can inherit PCD values from other SKUs.  This inheritance is limited to 
the scope of the DSC file.  This RFC has no impact to the PCD database or behavior of
PCD services.

The example Star provides at the end shows the equivalent set of PCD settings using
the current EDK II syntax and with this RFC's backwards compatible syntax extensions.

One way to think about this RFC is that a DSC file using the syntax in this RFC can
be converted to a DSC file without the RFC syntax.  In fact, that is what the 
implementation of this RFC would do to build the set of PCD values for each SKU.
 
Thanks,

Mike



> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Tim Lewis
> Sent: Wednesday, April 26, 2017 9:21 AM
> To: Zeng, Star <star.zeng@intel.com>; edk2-devel@lists.01.org
> Cc: Kinney, Michael D <michael.d.kinney@intel.com>; Gao, Liming
> <liming.gao@intel.com>
> Subject: Re: [edk2] [RFC] PCD: Extended SKU support 1 - inheritance
> 
> Star --
> 
> This assumes that the SKU ID is only used for PCDs, which is not the case. The
> SKU ID may be used by other components, and other components may use the
> 0|DEFAULT rule as well.
> 
> 1) There is no way to read this defaulting rule at runtime. The information is
> buried in the PCD database, but not available externally.
> 2) There is no way to read the contents of SKUID_IDENTIFIER when multiple SKUs
> are specified. While more than one SKU can be specified (separated by spaces),
> there is no way to pass multiple values into build.exe today, nor is there any
> way to identify which SKUs (out of the total list of SKUs) is supported on one
> build at runtime.
> 
> Tim
> 
> 
> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Zeng, Star
> Sent: Tuesday, April 25, 2017 5:40 AM
> To: edk2-devel@lists.01.org
> Cc: Kinney, Michael D <michael.d.kinney@intel.com>; Zeng, Star
> <star.zeng@intel.com>; Gao, Liming <liming.gao@intel.com>
> Subject: [edk2] [RFC] PCD: Extended SKU support 1 - inheritance
> 
> - Requirement
> Simplify the PCDs configuring for multiple SKUs in DSC.
> 
> 
> - Current limitation
> Non-DEFAULT SKU could only derive from DEFAULT SKU, but could not derive from
> another non-DEFAULT SKU.
> For example below, SkuA and SkuB could only derive from DEFAULT, but SkuB could
> not derive from SkuA.
> 
> [SkuIds]
>   0 | DEFAULT
>   1 | SkuA
>   2 | SkuB
> 
> 
> - Proposal: One non-DEFAULT SKU could be a derivative of another non-DEFAULT SKU.
> This proposal only extends DSC [SkuIds] section syntax and the extension is
> optional.
> This proposal keeps the backward compatibility with current SKU usage.
> BaseTools update is needed to support the syntax extension, and no any change in
> PCD database and driver is required.
> 
> DSC syntax:
>   [SkuIds]
>     SkuValue|SkuName[|ParentSkuName]
>       SkuValue: integer, 0 is reserved for DEFAULT SKU.
>       SkuName: string
>       ParentSkuName: string, optional, it is new introduced in this proposal and
> defines which SKU the PCD value will derive from for this SKU. The PCD value will
> derive from DEFAULT SKU for this SKU if the ParentSkuName is absent.
> 
> 
> - Example: SkuB is a derivative of SkuA, but not a derivative of DEFAULT.
> 
>   [SkuIds]
>     0 | DEFAULT
>     1 | SkuA
>     2 | SkuB | SkuA
> 
>   [PcdsDynamicDefault.Common.DEFAULT]
>     gXXXPkgTokenSpaceGuid.PcdXXXSignature|"DEFAULT"
>     gXXXPkgTokenSpaceGuid.PcdXXXConfig1|FALSE
>     gXXXPkgTokenSpaceGuid.PcdXXXConfig2|FALSE
>     gXXXPkgTokenSpaceGuid.PcdXXXConfig3|FALSE
> 
>   [PcdsDynamicDefault.Common.SkuA]
>     gXXXPkgTokenSpaceGuid.PcdXXXSignature|"SkuA"
>     gXXXPkgTokenSpaceGuid.PcdXXXConfig1|TRUE
>     gXXXPkgTokenSpaceGuid.PcdXXXConfig2|TRUE
>     # No need statement for PcdXXXConfig3 whose value will derive from DEFAULT
> SKU and be FLASE.
> 
>   [PcdsDynamicDefault.Common.SkuB]
>     gXXXPkgTokenSpaceGuid.PcdXXXSignature|" SkuB"
>     # No need statement for PcdXXXConfig1 and PcdXXXConfig2 whose values will
> derive from SkuA SKU and be TRUE.
>     gXXXPkgTokenSpaceGuid.PcdXXXConfig3|TRUE
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