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

["Brian J. Johnson" <brian.johnson@hpe.com>]

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Dandan,

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.

Thanks,

*Brian J. Johnson
*Enterprise X86 Lab

Hewlett Packard Enterprise

------------------------------------------------------------------------
*From:* Bi, Dandan [mailto:dandan.bi@intel.com]
*Sent:* Monday, June 22, 2020, 2:27 AM
*To:* Andrew Fish <afish@apple.com>, edk2-devel-groups-io 
<devel@edk2.groups.io>, brian.johnson@hpe.com <brian.johnson@hpe.com>
*Cc:* rfc@edk2.groups.io <rfc@edk2.groups.io>, Dong, Eric 
<eric.dong@intel.com>, Ni, Ray <ray.ni@intel.com>, Wang, Jian J 
<jian.j.wang@intel.com>, Wu, Hao A <hao.a.wu@intel.com>, Tan, Ming 
<ming.tan@intel.com>, Laszlo Ersek <lersek@redhat.com>, Bi, Dandan 
<dandan.bi@intel.com>
*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.
>
> Thanks,
>
> Dandan
>
> *From:* Andrew Fish <afish@apple.com>
> *Sent:* Saturday, June 20, 2020 2:04 AM
> *To:* edk2-devel-groups-io <devel@edk2.groups.io>; brian.johnson@hpe.com
> *Cc:* Bi, Dandan <dandan.bi@intel.com>; rfc@edk2.groups.io; Dong, Eric 
> <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>; Wang, Jian J 
> <jian.j.wang@intel.com>; Wu, Hao A <hao.a.wu@intel.com>; Tan, Ming 
> <ming.tan@intel.com>
> *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@hpe.com <mailto:brian.johnson@hpe.com>wrote:
>
>     On 6/18/20 2:01 AM, Dandan Bi wrote:
>
>         Hi All,
>
>         REF:https://bugzilla.tianocore.org/show_bug.cgi?id=2816
>         <https://bugzilla.tianocore.org/show_bug.cgi?id=2816>
>
>         We plan to separate two kinds of NULL class libraries for
>         Memory and serial handlers
>         from*MdeModulePkg/Universal/StatusCodeHandler/…/
>         StatusCodeHandlerPei/RuntimeDxe/Smm*modules.
>
>         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
>         library*MemoryStausCodeHandlerLib*and***SerialStatusCodeHandlerLib*with
>         different phase implementation
>         into*MdeModulePkg\Library\*directory.
>
>         The main tree structure may like below:
>
>         MdeModulePkg\Library
>
>         |------*MemoryStausCodeHandlerLib*
>
>         |------|------ PeiMemoryStausCodeHandlerLib.inf
>
>         |------|------ RuntimeDxeMemoryStatusCodeHandlerLib.inf
>
>         |------|------ SmmMemoryStausCodeHandlerLib.inf
>
>         |------*SerialStatusCodeHandlerLib*
>
>         |------|------ 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.
>
>         MdeModulePkg/Universal/StatusCodeHandler/Pei/StatusCodeHandlerPei.inf
>         {
>
>         <LibraryClasses>
>
>         NULL|MdeModulePkg/Library/MemoryStausCodeHandlerLib/PeiMemoryStausCodeHandlerLib.inf
>
>         NULL|MdeModulePkg/Library/SerialStatusCodeHandlerLib/PeiSerialStatusCodeHandlerLib.inf
>
>         …
>
>         }
>
>         MdeModulePkg/Universal/StatusCodeHandler/RuntimeDxe/StatusCodeHandlerRuntimeDxe.inf
>         {
>
>         <LibraryClasses>
>
>         NULL|MdeModulePkg/Library/MemoryStausCodeHandlerLib/RuntimeDxeMemoryStausCodeHandlerLib.inf
>
>         NULL|MdeModulePkg/Library/SerialStatusCodeHandlerLib/RuntimeDxeSerialStatusCodeHandlerLib.inf
>
>         …
>
>         }
>
>         MdeModulePkg/Universal/StatusCodeHandler/Smm/StatusCodeHandlerSmm.inf
>         {
>
>         <LibraryClasses>
>
>          NULL|MdeModulePkg/Library/MemoryStausCodeHandlerLib/SmmMemoryStausCodeHandlerLib.inf
>
>         NULL|MdeModulePkg/Library/SerialStatusCodeHandlerLib/SmmSerialStatusCodeHandlerLib.inf
>
>         …
>
>         }
>
>         Thanks,
>
>         Dandan
>
>     Dandan,
>
>     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
>     needed.
>
> 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.
>
> Thanks,
>
> Andrew Fish
>
>     Thanks,
>
>     --
>
>     *Brian J. Johnson
>     *Enterprise X86 Lab
>
>     Hewlett Packard Enterprise
>
>     *hpe.com* <x-msg://64/3D%22hpe.com%22>
>
>     
>

-

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