Re: visibility pf PcdSet

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 21 March 2017 at 02:23, Gao, Liming <liming.gao@intel.com> wrote:
> 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?
>

No. MIchael reported that DXE level drivers don't see the value
written to a patchable PCD by a SEC module, but as you confirmed, this
is expected behavior.

Thanks,
Ard.

>>-----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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