Re: visibility pf PcdSet

["Gao, Liming" <liming.gao@intel.com>]

Yes. Feature, FixedAtBuild and PatchableInModule PCD are module level; Dyanmic and DynamicEx are platform level. 
If you have case to share the data between the different modules, you can configure PCD as Dynamic PCD. 

Ard: do you meet with the issue on SetPcd() with dynamic PCD?  

Thanks
>-----Original Message-----
>From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Ard
>Biesheuvel
>Sent: Tuesday, March 21, 2017 2:20 AM
>To: Michael Zimmermann <sigmaepsilon92@gmail.com>
>Cc: edk2-devel@lists.01.org <edk2-devel@ml01.01.org>; Gao, Liming
><liming.gao@intel.com>; Laszlo Ersek <lersek@redhat.com>; Leif Lindholm
><leif.lindholm@linaro.org>
>Subject: Re: [edk2] visibility pf PcdSet
>
>On 20 March 2017 at 16:06, Michael Zimmermann
><sigmaepsilon92@gmail.com> wrote:
>> Do I understand correctly, that a PcdSet on a 'PcdsPatchableInModule'
>> is only visible to the current module?(SEC, driver, application, ...)
>
>Yes.
>
>> 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.
>>
>
>Indeed. The relocatable PrePi needs a patchable PCD because it assigns
>the value really early, in assembly code. But PrePi is a bit peculiar
>as well, and I am pretty use SetPcd() on dynamic PCDs would not work
>there either.
>
>> 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/76874be3d411bf8daac051718e20932
>e0bf97d70/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.
>>
>
>Ah yes, well spotted. To be honest, PrePi is a bit of a hack, and I
>actually recommend against it for new ports. However, for a self
>relocating image (which I think you need for your application), PrePi
>is really the only way to go.
>
>So the best way to pass information from PrePi to DXE is using HOBs.
>Actually, it might be best for you to clone HighmemDxe if you need it,
>and use a HOB instead.
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