Re: visibility pf PcdSet

[Laszlo Ersek <lersek@redhat.com>]

On 03/20/17 17:06, Michael Zimmermann wrote:
> Do I understand correctly, that a PcdSet on a 'PcdsPatchableInModule'
> is only visible to the current module?(SEC, driver, application, ...)

I've no experience with patchable-in-module PCDs.

> Because I've tested this and a PcdSet on
> gArmTokenSpaceGuid.PcdSystemMemoryBase inisde PrePi is not visible
> inside a DXE_DRIVER - which means that for everyone else the value is
> still 0x0.

No experience with PrePi...

> 
> If this is the case and I don't have some platform bug, then there is
> probably a bug in ArmVirtPkg's HighMemDxe where this Pcd is used in a
> DXE_DRIVER:
> https://github.com/tianocore/edk2/blob/76874be3d411bf8daac051718e20932e0bf97d70/ArmVirtPkg/HighMemDxe/HighMemDxe.c#L70
> It doesn't cause anything bad but it would show 'Failed to add System
> RAM @ START - END (Access Denied)' after calling AddMemorySpace for
> memory which has already been registered.

The DEC file that declares a given PCD provides the C language type for
it, the default value, the token space GUID and the token number, and
the set of "PCD flavors" that a specific platform DSC may choose for the
PCD.

In ArmVirtQemu.dsc, PcdSystemMemoryBase is defined under
PcdsFixedAtBuild, which works well, so I wouldn't say the error is in
HighMemDxe. Also, if some other DSC defined PcdSystemMemoryBase as a
dynamic one, it would again work well (assuming the PCD were set early
enough).

My point is, a platform DSC and a (DXE) driver have to work together.

Thanks
Laszlo