[edk2-platforms][RFC] SpiFlashCommonLib Refactor

["Michael Kubacki" <mikuback@linux.microsoft.com>]

Hello,

I'm planning to submit support for Standalone MM in SpiFlashCommonLib 
soon. Currently, there's quite a bit of duplication with SpiFlashCommonLib.

I would like to have this Standalone MM support be available in as 
consistent of a location as possible so I'd like to see if there is 
anything I can do to help clean this up in the early part of the patch 
series.


The library interface is currently defined in the following header files:

1. Platform\Intel\MinPlatformPkg\Include\Library\SpiFlashCommonLib.h

2. Silicon\Intel\SimicsIch10Pkg\Include\Library\SpiFlashCommonLib.h

3. Silicon\Intel\KabylakeSiliconPkg\Pch\Include\Library\SpiFlashCommonLib.h

4. 
Silicon\Intel\CoffeelakeSiliconPkg\Pch\Include\Library\SpiFlashCommonLib.h


Instances of SmmSpiFlashCommonLib implementation exist in a mix of 
platform and silicon packages:

1. 
Silicon\Intel\SimicsIch10Pkg\Library\SmmSpiFlashCommonLib\SmmSpiFlashCommonLib.inf

2. 
Platform\Intel\TigerlakeOpenBoardPkg\Library\SmmSpiFlashCommonLib\SmmSpiFlashCommonLib.inf

3. 
Silicon\Intel\KabylakeSiliconPkg\Pch\Library\SmmSpiFlashCommonLib\SmmSpiFlashCommonLib.inf

4. 
Silicon\Intel\CoffeelakeSiliconPkg\Pch\Library\SmmSpiFlashCommonLib\SmmSpiFlashCommonLib.inf

5. 
Platform\Intel\MinPlatformPkg\Flash\Library\SpiFlashCommonLibNull\SpiFlashCommonLibNull.inf


The library class is currently consumed in the following INFs:

1. Platform\Intel\MinPlatformPkg\Flash\SpiFvbService\SpiFvbServiceSmm.inf

2. 
Platform\Intel\MinPlatformPkg\Flash\SpiFvbService\SpiFvbServiceStandaloneMm.inf


My understanding is:

1. The header file is defined in each silicon package because silicon 
cannot depend upon platform (i.e. the MinPlatformPkg header).

2. The header is present in each silicon package because the 
implementation is silicon-specific and these packages cannot depend on 
one another.

3. The header is defined in MinPlatformPkg because MinPlatformPkg should 
be silicon vendor agnostic (cannot depend on the silicon packages).

4. The header is needed in MinPlatformPkg because the SpiFvbService 
there depends on SPI flash operations implemented in SpiFlashCommonLib.


Here's an initial proposal:

1. Consolidate the library interface into a single header. In 
IntelSiliconPkg?

2. Consolidate library implementation into a single instance. In 
IntelSiliconPkg?

3. Move SpiFvbServiceXyz out of MinPlatformPkg.
    3.a. Make a "SPI flash" feature?
    3.b. Allow the Intel implementation of this feature to depend on 
SpiFlashCommonLib defined in IntelSiliconPkg.

Intel board packages could then use the SpiFlashCommonLib from 
IntelSiliconPkg (a generation specific instance could be created if 
needed) and use the SpiFvbServiceXyz driver from the "SpiFlash" feature.

Look forward to your thoughts and feedback.

Thanks,
Michael