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Subject: Re: [edk2-devel] Is there an ACPI solution for ARM (or other) platforms that don't have DRAM under 4 GiB?
To: devel@edk2.groups.io, afish@apple.com
References: <814F375B-BF55-44E3-8E11-8C322ACA26C6@apple.com>
From: "Laszlo Ersek" <lersek@redhat.com>
Cc: "Ard Biesheuvel (TianoCore)" <ardb+tianocore@kernel.org>
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Date: Fri, 19 Mar 2021 20:41:10 +0100
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adding Ard, comment below

On 03/19/21 02:47, Andrew Fish via groups.io wrote:
> Some one was asking me this question and I did not know the answer?
> It looks like the stock ACPI stack needs memory under 4 GiB to fill
> in 32-bits as it was the 1990’s when that got written down. Is there
> support on TianoCore to implement ACPI on a platform that does not
> have memory < 4 GiB in its address map?

Yes, I think so. The most relevant commits seem to be:

  f9bbb8d9c3f0 MdeModulePkg: AcpiTableDxe: make 4 GB table allocation limit optional

  f859c6796f40 MdeModulePkg/AcpiTableDxe: consider version mask when removing tables
  09da11081915 MdeModulePkg/BootGraphicsResourceTableDxe: don't allocate below 4 GB

  0e0ae47da6bd MdeModulePkg/AcpiTableDxe: use pool allocations when possible
  cf299745ae66 MdeModulePkg/AcpiTableDxe: use pool allocation for RSDT/XSDT if possible
  8ead7af22bc5 MdeModulePkg/AcpiTableDxe: use pool allocation for RSDP if possible

This should be possible to control through PcdAcpiExposedTableVersions.

Thanks
Laszlo