[edk2-devel] setting PcdPlatformBootTimeOut in PlatformBootManagerLib

[Laszlo Ersek]

On 03/02/20 00:13, Laszlo Ersek wrote:
> Hi Ray,
> 
> OvmfPkg and ArmVirtPkg platforms set PcdPlatformBootTimeOut in their
> PlatformBootManagerLib instances, in BeforeConsole(). This generally
> works, except for one aspect: in BdsEntry(), the Timeout UEFI variable
> is set from the PCD before BeforeConsole() is called.
> 
> The Timeout variable is in this case purely informative, but I'd still
> like it to reflect the PCD's value. Given that I'd like to keep the
> subject PcdSet16S() call in PlatformBootManagerLib, I see two options:
> 
> (1) Modify BdsEntry(): re-check the value of the PCD a bit before
> BdsWait() -- when the PCD is really needed --, and if it has changed
> relative to the first seen value, store the new PCD value to the UEFI
> variable *again*.
> 
> This would keep platforms happy that expect Timeout to already carry the
> PCDs value upon entering BeforeConsole(), and it would allow platforms
> to re-set the PCD (and Timeout too) in either BeforeConsole() or
> AfterConsole().
> 
> (2) Alternatively, add a CONSTRUCTOR function to the
> PlatformBootManagerLib instances for setting the PCD before BdsEntry()
> is invoked at all. I'm a bit concerned about this, as we'd have to
> ensure that *all* the lib instances that participate in this PCD setting
> (including the lib instances that let us calculate the value) have
> CONSTRUCTOR functions (otherwise the topological sorting of CONSTRUCTOR
> calls is not complete).

(3) We could also just rewrite Timeout ourselves, in
PlatformBootManagerLib, where we set the PCD.

Thanks
Laszlo


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