Re: [edk2-devel] [edk2-rfc] MdeModulePkg/StatusCodeHandler: Separate NULL class libraries for Memory and serial handlers from MdeModulePkg/Universal/StatusCodeHandler modules

Brian J. Johnson


The Status Code Protocol/PPI is the high-level interface which is being implemented.  The ReportStatusCodeRouter module implements this in terms of the ReportStatusCodeHandler Protocol/PPI.  That allows multiple ReportStatusCodeHandler modules to be used at once, so they can each react to different types of status codes, or report them through multiple channels.  That sort of multiplexing seems like a useful feature.

Now we're considering adding a mechanism which allows registering status code handlers via NULL libraries, rather than via the protocol/PPI.  That sounds like exactly what ReportStatusCodeRouter is intended for.  It wouldn't really change its scope, it would just make it more flexible.  Adding this feature via a StatusCodeHandler module wouldn't improve modularity, it would just add complexity.  As an OEM, adding a custom handler would look the same to me either way:  I would have to add the NULL class library to a MdeModulePkg driver's entry in my .dsc file.  It doesn't matter to me whether it's the ReportStatusCodeRouter or StatusCodeHandler module.  And if I can do it in ReportStatusCodeRouter, then I don't need to include any StatusCodeHandler modules in the build at all.  That saves code space and reduces the number of modules in the APRIORI list, which are both good things.

ReportStatusCodeRouterPei already has to track registered handlers in PEI when running from ROM (it uses a HOB.)  Tracking handlers from NULL libraries wouldn't be any harder.  In fact, it looks like it could just export the Register() function to the NULL libraries, and they could call it in their constructors.

I think using NULL libraries for status code handlers is a great idea.  I'd just like to take that opportunity to reduce the complexity of the overall status code stack while we're at it.


*Brian J. Johnson
*Enterprise X86 Lab

Hewlett Packard Enterprise

*From:* Bi, Dandan []
*Sent:* Monday, June 22, 2020, 2:27 AM
*To:* Andrew Fish <afish@...>, edk2-devel-groups-io <>, brian.johnson@... <brian.johnson@...>
*Cc:* <>, Dong, Eric <eric.dong@...>, Ni, Ray <>, Wang, Jian J <>, Wu, Hao A <hao.a.wu@...>, Tan, Ming <ming.tan@...>, Laszlo Ersek <lersek@...>, Bi, Dandan <>
*Subject:* [edk2-devel] [edk2-rfc] MdeModulePkg/StatusCodeHandler: Separate NULL class libraries for Memory and serial handlers from MdeModulePkg/Universal/StatusCodeHandler modules

Hi Brian,

Personally, I prefer to add the NULL class Library to StatusCodeHandler modules.

1. I think we should make the functionality of each module clear and
separated. It may also be why we added ReportStatusCodeRouter and
StatusCodeHandler modules in edk2 repo before.

ReportStatusCodeRouter modules are responsible for producing Status Code Protocol/PPI and Report Status Code Handler Protocol/PPI, and StatusCodeHandler modules are responsible for producing handlers (Handlers can be provided by NULL class Libraries in this RFC).

 So, that’s why I don’t want to add the NULL class Library to ReportStatusCodeRouter modules directly, which change the functionality scope of existing modules.

2. I agree that we have a lot of layers of indirection now, but what
we may gain is the good modularity. And you also mentioned that
one or more StatusCodeHandler Modules may be used. We also want to
achieve that only the StatusCodeHandler modules in MdeModulePkg
can be used after this separation, platform can only add its own
handler Libs to meet its requirement.

3. As Andrew mentioned below, if add the libraries to
ReportStatusCodeRouter, there will be some issue we need to fix,
which seems also make the code logic a little tricky to me.



*From:* Andrew Fish <afish@...>
*Sent:* Saturday, June 20, 2020 2:04 AM
*To:* edk2-devel-groups-io <>; brian.johnson@...
*Cc:* Bi, Dandan <>;; Dong, Eric <eric.dong@...>; Ni, Ray <>; Wang, Jian J <>; Wu, Hao A <hao.a.wu@...>; Tan, Ming <ming.tan@...>
*Subject:* Re: [edk2-devel] [edk2-rfc] MdeModulePkg/StatusCodeHandler: Separate NULL class libraries for Memory and serial handlers from MdeModulePkg/Universal/StatusCodeHandler modules

On Jun 19, 2020, at 10:29 AM, Brian J. Johnson
<brian.johnson@... <mailto:brian.johnson@...>wrote:

On 6/18/20 2:01 AM, Dandan Bi wrote:

Hi All,


We plan to separate two kinds of NULL class libraries for
Memory and serial handlers

The benefit we want to gain from this separation is to 1) make
the code clear and easy to maintain, 2) make platform flexible
to choose any handler library they need, and it also can
reduce image size since the unused handlers can be excluded.

If you have any concern or comments for this separation,
please let me know.

We plan to add new separated NULL class
different phase implementation

The main tree structure may like below:



|------|------ PeiMemoryStausCodeHandlerLib.inf

|------|------ RuntimeDxeMemoryStatusCodeHandlerLib.inf

|------|------ SmmMemoryStausCodeHandlerLib.inf


|------|------ PeiSerialStatusCodeHandlerLib.inf

|------|------ RuntimeDxeSerialStatusCodeHandlerLib.inf

|------|------ SmmSerialStatusCodeHandlerLib.inf



We will update existing platform use cases in edk2 and
edk2-platform repo to cover the new NULL class library to make
sure this change doesn’t impact any platform.

After this separation, StatusCodeHandler module usage will
like below, and it’s also very flexible for platform to cover
more handler libraries to meet their requirements.



















We'll have a lot of layers of indirection....  The
ReportStatusCodeRouter modules will call one or more
StatusCodeHandlerModules, and the standard StatusCodeHandler
modules will call multiple StatusCodeHandlerLib libraries.

How about adding StatusCodeHandlerLib support directly to the
ReportStatusCodeRouter modules?  Then platforms could omit the
StatusCodeHandler modules if they're only using the open-source
code.  That sounds like less overhead since fewer modules would be

I think the need to execute from ROM makes this tricky.

It looks to me that it is easy to move from PCD to libs for the StatusCodeHandler since registration is basically `RscHandlerPpi->Register (SerialStatusCodeReportWorker);`. The issue I see is the ReportStatusCodeRouter publishes RscHandlerPpi after the PEIMs constructor has been called and if the PEIM. Given globals don’t work when running from ROM you would have to do something like publish a HOB in the library constructor and then have the GenericStatusCodePeiEntry() walk the HOBs and install the handlers. So I guess it is a little easier than I 1st thought when I started writing this mail, but it would require a new public API.


Andrew Fish



*Brian J. Johnson
*Enterprise X86 Lab

Hewlett Packard Enterprise

** <x-msg://64/>


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