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

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

> My personal conclusion in that thread was [1], and correspondingly,
> commit 5087a0773645 ("ArmVirtPkg/FdtPL011SerialPortLib: initialize
> implicitly", 2023-10-07). In the end, the only tractable solution was to
> initialize the serial port (hardware, and library instance) exactly
> once, in (a) the constructor, or (b) the explicit SerialPortInitialize()
> call, or (c) any SerialPortLib API, whichever occurred first. (And (a)
> and (b) can be coalesced, because SerialPortInitialize() can be marked
> as the constructor for the lib instance.)
>
> [1] http://mid.mail-archive.com/542db9e1-cd28-27a2-3a98-5b0c85cd7c79@redhat.com
>      https://edk2.groups.io/g/devel/message/109235
>
> Laszlo
>
In my personal thinking, It's better to make new interface like

RETURN_STATUS
EFIAPI
SerialPortInitializeEarly (
VOID
   );

to solve this problem.

Because, It makes a memory permission fault
when we call SerialPortInitialize like
ArmVirtPkg/Library/FdtPL011SerialPortLib
where try to modify global variable.

At the _ModuleEntryPoint of StandAloneMmCore which is FIRST entry from TF-A
All of Image area is mapped as RO+X, so before load StandaloneMmCore,
We couldn't write global variable.

the purposes of above interface are:
     - Initalize serial port to use in early environment only (like
StandAloneMmCore Entry Point) where couldn't write global variable by
static information (FixedPcd).
     - It presume that all setting configured by it will be overwritten
by SerialPortInitialize.




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