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Re: [Xen-devel] [edk2] [PATCH RFC v2 1/7] MdeModulePkg: introduce PcdPciAllowFullEnumeration ... [and one more message]


The PCD declaration in the DEC file declares the PCD type the PCD is allowed to 
have.  For this specific PCD, you may want to allow it to be FixedAtBuild or 
PatahcbleInModule or Dynamic or DynamicEx.  This provides the maximum 

For future DUET use cases, the DSC file could set it to FixedAtBuild, so the 
full enumeration code could be optimized away.

For OVMF use cases where you want to be able to enable/disable enumeration, you 
can set it to DynamicEx in the DSC file.  PciBusDxe built with this config 
would include support for full and no enumeration.  If the DynamicEx subtype is 
set to HII, then a UEFI Variable setting can enable/disable enumeration and 
could be set in FD image externally.  Likewise, if the DynamicEx subtype is set 
to VPD (Vital Product Data), then the VPD area could be patched in the FD image 

Best regards,


-----Original Message-----
From: Wei Liu [mailto:wei.liu2@xxxxxxxxxx] 
Sent: Monday, November 25, 2013 2:56 AM
To: Kinney, Michael D
Cc: Jordan Justen; edk2-devel@xxxxxxxxxxxxxxxxxxxxx; Tian, Feng; Wei Liu; 
Subject: Re: [edk2] [PATCH RFC v2 1/7] MdeModulePkg: introduce 
PcdPciAllowFullEnumeration ... [and one more message]

On Mon, Nov 25, 2013 at 03:12:04AM +0000, Kinney, Michael D wrote:
> Jordan,
> I agree that removing code duplication is a good idea.
> I believe we can make the one in the MdeModulePkg functional
> everywhere.  Size will be the only remaining difference.  This can be
> addressed longer term.  If the proposed PCD is configured as
> FixedAtBuild in a DSC file, we should be able to get the optimized
> code generation for the PciBusDxe to remove all the code/data that is
> only used for PCI Enumeration.  Then the PciBusNoEnumeration could be
> retired.

Forgive my ignorance -- is it possible to change FixedAtBuild PCD during
runtime? Jordan had the idea to disable / enable PCI enumeration during
runtime, so that we can have one single binary for all OVMF users.

> I have no issues with adding a PCD to make the PciBusDxe in the
> MdeModulePkg skip enumeration all together.

Cool, thank you for confirming this.


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