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

On Mon, Nov 25, 2013 at 11:27:14PM +0000, Kinney, Michael D wrote:
> Wei,
> 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 flexibility.
> 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 externally.
> Best regards,

Thanks for the explanation.

Currently in this patch this PCD in Mde is defined as [FixedAtBuild,
Dynamic, DynamicEx] so I suppose I am doing the right thing. Do you think
it is necessary to add in PatachbleInModule?

(note to self: state clearly the types of the PCD in the commit message
in next version)


> Mike
> -----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; 
> xen-devel
> 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.
> Wei.

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