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Date: Tue, 17 Jan 2023 15:38:18 +0100
From: "Gerd Hoffmann" <kraxel@redhat.com>
To: "Boeuf, Sebastien" <sebastien.boeuf@intel.com>
Cc: "Yao, Jiewen" <jiewen.yao@intel.com>,
	"Justen, Jordan L" <jordan.l.justen@intel.com>,
	"devel@edk2.groups.io" <devel@edk2.groups.io>,
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Subject: Re: [OVMF] What would be the best way to make PcdPciMmio64Size dynamic?
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On Tue, Jan 17, 2023 at 02:10:08PM +0000, Boeuf, Sebastien wrote:
> Hi,
> 
> Looking at the hardcoded limitation provided by PcdPciMmio64Size
> (32GiB), I was wondering what would be the best approach to make this a
> bit more dynamic?
> 
> I know that for QEMU, the fw_cfg mechanism can be used to override the
> value of PcdPciMmio64Size, but this isn't something Cloud Hypervisor or
> other VMMs can implement given they don't support fw_cfg at all.
> 
> Would it be acceptable to dynamically compute PcdPciMmio64Size from the
> physical address space? Given the reason why PcdPciMmio64Size can't be
> increased is to make sure it can support host with small address space
> (such as 36 bits), we could introduce a very simple function that would
> determine the available address space and consider PcdPciMmio64Size
> being half the size.

Sure, check master branch, the code is already there.  Should just be a
matter of wiring up the function calls for cloundhv, and you can
probably call PlatformAddressWidthFromCpuid() with QemuQuirk = false
unconditionally.

take care,
  Gerd