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

["levi.yun" <yeoreum.yun@arm.com>]

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.








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