This will let QEMU's "-no-acpi" option exclusively expose DT vs. ACPI to
the guest. Showing both is never needed (it is actually detrimental to the
adoption of standards, such as SBSA / SBBR).

* Without "-no-acpi", the firmware logs (from PlatformHasAcpiDtDxe)

> Found FwCfg @ 0x9020008/0x9020000
> Found FwCfg DMA @ 0x9020010
> InstallProtocolInterface: [EdkiiPlatformHasAcpi] 0

plus the usual messages. Later the guest kernel logs

> [    0.000000] efi:  SMBIOS 3.0=0x13bdb0000  ACPI 2.0=0x138440000
>                      MEMATTR=0x13a675018

before it lists the ACPI tables one by one.

In addition, in the guest, the "/sys/firmware/devicetree/*" shell pattern
matches no files, while the "/sys/firmware/acpi/tables/*" pattern matches
the ACPI tables.

* With "-no-acpi", the firmware logs:

> PlatformHasAcpiDtDxe | Found FwCfg @ 0x9020008/0x9020000
> PlatformHasAcpiDtDxe | Found FwCfg DMA @ 0x9020010
> PlatformHasAcpiDtDxe | InstallProtocolInterface:
> PlatformHasAcpiDtDxe | [EdkiiPlatformHasDeviceTree] 0
> FdtClientDxe         | OnPlatformHasDeviceTree: exposing DTB @
> FdtClientDxe         | 0x13FFBF000 to OS
> ...
> DXE_CORE             | Driver [AcpiTableDxe] was discovered but not
> DXE_CORE             | loaded!!
> DXE_CORE             | Driver [QemuFwCfgAcpiPlatform] was discovered but
> DXE_CORE             | not loaded!!
> ...
> RamDiskDxe           | RamDiskAcpiCheck: Cannot locate the EFI ACPI
> RamDiskDxe           | Table Protocol, unable to publish RAM disks to
> RamDiskDxe           | NFIT.

(BootGraphicsResourceTableDxe's ReadyToBoot callback --
InstallBootGraphicsResourceTable() -- handles the lack of
EFI_ACPI_TABLE_PROTOCOL silently.) Later the guest kernel logs

> [    0.000000] efi:  SMBIOS 3.0=0x13bdb0000  MEMATTR=0x138caa018

In addition, in the guest, the "/sys/firmware/devicetree/*" shell pattern
matches the directory "/sys/firmware/devicetree/base", which contains a
large number of DT nodes, while the "/sys/firmware/acpi/tables/*" pattern
matches no files.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1430262
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 MEMATTR log from repeated testing with Fedora guest (ACPI
      case) [Ard]
    - extend the commit message with "/sys/firmware/devicetree/*" and
      "/sys/firmware/acpi/tables/*" pattern matching in the guest
    - drop ArmVirtPkg.dec package dependency -- with the removal of the
      "pure ACPI boot" PCD dependency, ArmVirtPkg.dec actually becomes
      superfluous
    - adapt patch to protocol -> generic GUID renaming
    - pick up Ard's R-b

 ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.inf |  7 +--
 ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.c   | 45 ++++++++++++--------
 2 files changed, 29 insertions(+), 23 deletions(-)

diff --git a/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.inf b/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.inf
index e77bb04e2e9d..3fcbb6b080d8 100644
--- a/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.inf
+++ b/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.inf
@@ -25,15 +25,15 @@ [Sources]
   PlatformHasAcpiDtDxe.c
 
 [Packages]
-  ArmVirtPkg/ArmVirtPkg.dec
   EmbeddedPkg/EmbeddedPkg.dec
   MdeModulePkg/MdeModulePkg.dec
   MdePkg/MdePkg.dec
+  OvmfPkg/OvmfPkg.dec
 
 [LibraryClasses]
   BaseLib
   DebugLib
-  PcdLib
+  QemuFwCfgLib
   UefiBootServicesTableLib
   UefiDriverEntryPoint
 
@@ -41,8 +41,5 @@ [Guids]
   gEdkiiPlatformHasAcpiGuid       ## SOMETIMES_PRODUCES ## PROTOCOL
   gEdkiiPlatformHasDeviceTreeGuid ## SOMETIMES_PRODUCES ## PROTOCOL
 
-[FeaturePcd]
-  gArmVirtTokenSpaceGuid.PcdPureAcpiBoot ## CONSUMES
-
 [Depex]
   TRUE
diff --git a/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.c b/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.c
index a718ce1b5a7b..8932dacabec5 100644
--- a/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.c
+++ b/ArmVirtPkg/PlatformHasAcpiDtDxe/PlatformHasAcpiDtDxe.c
@@ -17,7 +17,7 @@
 #include <Guid/PlatformHasDeviceTree.h>
 #include <Library/BaseLib.h>
 #include <Library/DebugLib.h>
-#include <Library/PcdLib.h>
+#include <Library/QemuFwCfgLib.h>
 #include <Library/UefiBootServicesTableLib.h>
 
 EFI_STATUS
@@ -27,18 +27,27 @@ PlatformHasAcpiDt (
   IN EFI_SYSTEM_TABLE *SystemTable
   )
 {
-  EFI_STATUS Status;
-
-  Status = EFI_SUCCESS;
+  EFI_STATUS           Status;
+  FIRMWARE_CONFIG_ITEM FwCfgItem;
+  UINTN                FwCfgSize;
 
   //
   // If we fail to install any of the necessary protocols below, the OS will be
   // unbootable anyway (due to lacking hardware description), so tolerate no
   // errors here.
   //
-  // Always make ACPI available on 64-bit systems.
-  //
-  if (MAX_UINTN == MAX_UINT64) {
+  if (MAX_UINTN == MAX_UINT64 &&
+      !EFI_ERROR (
+         QemuFwCfgFindFile (
+           "etc/table-loader",
+           &FwCfgItem,
+           &FwCfgSize
+           )
+         )) {
+    //
+    // Only make ACPI available on 64-bit systems, and only if QEMU generates
+    // (a subset of) the ACPI tables.
+    //
     Status = gBS->InstallProtocolInterface (
                     &ImageHandle,
                     &gEdkiiPlatformHasAcpiGuid,
@@ -48,21 +57,21 @@ PlatformHasAcpiDt (
     if (EFI_ERROR (Status)) {
       goto Failed;
     }
+
+    return Status;
   }
 
   //
-  // Expose the Device Tree unless PcdPureAcpiBoot is set.
+  // Expose the Device Tree otherwise.
   //
-  if (!FeaturePcdGet (PcdPureAcpiBoot)) {
-    Status = gBS->InstallProtocolInterface (
-                    &ImageHandle,
-                    &gEdkiiPlatformHasDeviceTreeGuid,
-                    EFI_NATIVE_INTERFACE,
-                    NULL
-                    );
-    if (EFI_ERROR (Status)) {
-      goto Failed;
-    }
+  Status = gBS->InstallProtocolInterface (
+                  &ImageHandle,
+                  &gEdkiiPlatformHasDeviceTreeGuid,
+                  EFI_NATIVE_INTERFACE,
+                  NULL
+                  );
+  if (EFI_ERROR (Status)) {
+    goto Failed;
   }
 
   return Status;
-- 
2.9.3


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