Re: [edk2-devel] [Patch] MdeModulePkg DxeCore: Fix for missing MAT update

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

Laszlo:

> -----Original Message-----
> From: devel@edk2.groups.io [mailto:devel@edk2.groups.io] On Behalf Of Laszlo Ersek
> Sent: Wednesday, August 14, 2019 11:13 PM
> To: Gao, Liming <liming.gao@intel.com>; Kinney, Michael D <michael.d.kinney@intel.com>; devel@edk2.groups.io
> Cc: Mike Turner <miketur@microsoft.com>; Wang, Jian J <jian.j.wang@intel.com>; Wu, Hao A <hao.a.wu@intel.com>; Bi, Dandan
> <dandan.bi@intel.com>
> Subject: Re: [edk2-devel] [Patch] MdeModulePkg DxeCore: Fix for missing MAT update
> 
> On 08/14/19 16:00, Gao, Liming wrote:
> > Laszlo:
> 
> >
> > I cherry pick this patch from Mu project with the minimal change.
> > I can update the comment style.
> 
> Yes, please. Thanks!
> 
> >> The gEfiMemoryTypeInformationGuid HOB is supposed to be built -- if it
> >> is built at all -- no later than in the DXE IPL PEIM (if VariablePei is
> >> included in the platform, and the underlying UEFI variable exists). Is
> >> that correct?
> >>
> > gEfiMemoryTypeInformationGuid HOB is installed by platform PEI.
> 
> Yes, that's what I meant by "no later than in the DXE IPL PEIM".
> 
> > If the platform PEI doesn't install this HOB, it means this feature is disabled.
> 
> PlatformPei is supposed to build the HOB in the first place, yes.
> 
> However, if it doesn't, then there still may be a feedback loop between
> the DXE IPL PEIM and BDS. The former builds the HOB from the UEFI
> variable, and the latter updates the variable (as I understand) for
> future boots.
> 
UEFI variable is created by BDS only when HOB can be found. 
If Platform PEIM doesn't build HOB, DxeIpl will not build HOB, 
then BDS will not create UEFI variable. If so, there is no HOB in 
every boot. 

Thanks
Liming
> Thanks
> Laszlo
> 
>