This reverts commit 78c41ff519b187d8979cda7074f007a6323f9acd.

We realized that DXE drivers that are independent of AcpiPlatformDxe (that
is, independent of QEMU's ACPI generation), such as RamDiskDxe and
BootGraphicsResourceTableDxe, may produce and/or manipulate ACPI tables,
at driver dispatch or even at Ready To Boot.

This makes it unsafe for us to check for ACPI presence in the UEFI system
config table in a Ready To Boot callback, in order to decide about
exposing the DT.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---

Notes:
    v3:
    - pick up Ard's R-b

 ArmVirtPkg/ArmVirtPkg.dec                | 10 ++++++++++
 ArmVirtPkg/ArmVirtQemu.dsc               |  5 +++++
 ArmVirtPkg/FdtClientDxe/FdtClientDxe.inf |  5 +++--
 ArmVirtPkg/FdtClientDxe/FdtClientDxe.c   | 16 +++++-----------
 4 files changed, 23 insertions(+), 13 deletions(-)

diff --git a/ArmVirtPkg/ArmVirtPkg.dec b/ArmVirtPkg/ArmVirtPkg.dec
index efe83a383d55..a5ec42166445 100644
--- a/ArmVirtPkg/ArmVirtPkg.dec
+++ b/ArmVirtPkg/ArmVirtPkg.dec
@@ -58,3 +58,13 @@ [PcdsFixedAtBuild, PcdsPatchableInModule]
   # EFI_VT_100_GUID.
   #
   gArmVirtTokenSpaceGuid.PcdTerminalTypeGuidBuffer|{0x65, 0x60, 0xA6, 0xDF, 0x19, 0xB4, 0xD3, 0x11, 0x9A, 0x2D, 0x00, 0x90, 0x27, 0x3F, 0xC1, 0x4D}|VOID*|0x00000007
+
+[PcdsFeatureFlag]
+  #
+  # Pure ACPI boot
+  #
+  # Inhibit installation of the FDT as a configuration table if this feature
+  # PCD is TRUE. Otherwise, the OS is presented with both a DT and an ACPI
+  # description of the platform, and it is up to the OS to choose.
+  #
+  gArmVirtTokenSpaceGuid.PcdPureAcpiBoot|FALSE|BOOLEAN|0x0000000a
diff --git a/ArmVirtPkg/ArmVirtQemu.dsc b/ArmVirtPkg/ArmVirtQemu.dsc
index 4f686faa559c..4b556f309a6c 100644
--- a/ArmVirtPkg/ArmVirtQemu.dsc
+++ b/ArmVirtPkg/ArmVirtQemu.dsc
@@ -34,6 +34,7 @@ [Defines]
   # -D FLAG=VALUE
   #
   DEFINE SECURE_BOOT_ENABLE      = FALSE
+  DEFINE PURE_ACPI_BOOT_ENABLE   = FALSE
 
 !include ArmVirtPkg/ArmVirt.dsc.inc
 
@@ -94,6 +95,10 @@ [PcdsFeatureFlag.common]
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutGopSupport|TRUE
   gEfiMdeModulePkgTokenSpaceGuid.PcdConOutUgaSupport|FALSE
 
+!if $(PURE_ACPI_BOOT_ENABLE) == TRUE
+  gArmVirtTokenSpaceGuid.PcdPureAcpiBoot|TRUE
+!endif
+
 [PcdsFixedAtBuild.common]
   gArmPlatformTokenSpaceGuid.PcdCoreCount|1
 !if $(ARCH) == AARCH64
diff --git a/ArmVirtPkg/FdtClientDxe/FdtClientDxe.inf b/ArmVirtPkg/FdtClientDxe/FdtClientDxe.inf
index 9861f41e968b..00017727c32c 100644
--- a/ArmVirtPkg/FdtClientDxe/FdtClientDxe.inf
+++ b/ArmVirtPkg/FdtClientDxe/FdtClientDxe.inf
@@ -37,16 +37,17 @@ [LibraryClasses]
   HobLib
   UefiBootServicesTableLib
   UefiDriverEntryPoint
-  UefiLib
 
 [Protocols]
   gFdtClientProtocolGuid                  ## PRODUCES
 
 [Guids]
-  gEfiAcpi20TableGuid
   gEfiEventReadyToBootGuid
   gFdtHobGuid
   gFdtTableGuid
 
+[FeaturePcd]
+  gArmVirtTokenSpaceGuid.PcdPureAcpiBoot
+
 [Depex]
   TRUE
diff --git a/ArmVirtPkg/FdtClientDxe/FdtClientDxe.c b/ArmVirtPkg/FdtClientDxe/FdtClientDxe.c
index 21c1074e331c..4cf79f70cb2a 100644
--- a/ArmVirtPkg/FdtClientDxe/FdtClientDxe.c
+++ b/ArmVirtPkg/FdtClientDxe/FdtClientDxe.c
@@ -17,11 +17,9 @@
 #include <Library/DebugLib.h>
 #include <Library/UefiDriverEntryPoint.h>
 #include <Library/UefiBootServicesTableLib.h>
-#include <Library/UefiLib.h>
 #include <Library/HobLib.h>
 #include <libfdt.h>
 
-#include <Guid/Acpi.h>
 #include <Guid/EventGroup.h>
 #include <Guid/Fdt.h>
 #include <Guid/FdtHob.h>
@@ -318,16 +316,12 @@ OnReadyToBoot (
   )
 {
   EFI_STATUS      Status;
-  VOID            *Table;
 
-  //
-  // Only install the FDT as a configuration table if we are not exposing
-  // ACPI 2.0 (or later) tables. Note that the legacy ACPI table GUID has
-  // no meaning on ARM since we need at least ACPI 5.0 support, and the
-  // 64-bit ACPI 2.0 table GUID is mandatory in that case.
-  //
-  Status = EfiGetSystemConfigurationTable (&gEfiAcpi20TableGuid, &Table);
-  if (EFI_ERROR (Status) || Table == NULL) {
+  if (!FeaturePcdGet (PcdPureAcpiBoot)) {
+    //
+    // Only install the FDT as a configuration table if we want to leave it up
+    // to the OS to decide whether it prefers ACPI over DT.
+    //
     Status = gBS->InstallConfigurationTable (&gFdtTableGuid, mDeviceTreeBase);
     ASSERT_EFI_ERROR (Status);
   }
-- 
2.9.3


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