Re: [edk2-devel] [PATCH v1 1/1] StandaloneMmPkg: Initialise serial port early in StandaloneMmEntryPoint

["Oliver Smith-Denny" <osde@linux.microsoft.com>]

On 1/5/2024 9:22 AM, levi.yun wrote:
> 
> Hi Ard :)
> 
>> So now we will always initialize the serial port in the entrypoint
>> only because DebugLib might use it later with doing the
>> initialization.
>>
>> That doesn't sound quite correct to me.
>>
>> Could you explain why we cannot rely on DebugLib to call the
>> initializer / constructor at the right time?
> Because, DebugLib constructor which use serial port is called in
> StandAloneMmMain function.
> But, this constrcutor is in _ModuleEntryPoint in StandAloneMmCoreEntry.
> 
> That means all DEBUG used in _ModuleEntryPoint can use uninitialized
> serial port.
> one of typical example is GetSpmVersion function.
> 
>      _ModuleEntryPoint (in StandAloneMmCoreEntry)
> 
>       // Hazard Area start
>          GetSpmVersion
>              DEBUG (DEBUG_INFO, xxx)  // It could be use uninitalized
> Serial port.
> 
>          ...
>      //  Hazard Area end
>          ProcessModuleEntryPointList (StandAloneMmMain)
>              ProcessLibraryConstructorList // Here. call DebugLib
> constructor with SerialPortIntialize
> 
> When you see above, I would be clear. between Hazard Area Start to
> Hazard Area End.
> DEBUG macro would use uninitailized Serial port if that's not
> initialized by TF-A.
> 
> So, It should be call SerialPortInitialized at the _ModuleEntryPoint.

+ Laszlo

This sounds very similar to our DxeCore early serial logging discussion
a couple months ago :).

Laszlo wrote up a good summary here: 
https://edk2.groups.io/g/devel/topic/101203427#109235.

If I am understanding correctly, this would be the "lower left" in
Laszlo's diagram.

Standalone MM is likely smaller missing window than in DxeCore, but
some important information could be lost there (like the SPM version
called out, which could be very important for debugging early crashes).

So this goes back to should be we have a more generic solution for the
cores to use early logging, by fixing the SerialPortLibs? I'll parse
this more and reread the old thread further, still paging the info back
in.

Oliver


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