The presence of this GUID in the PPI database, and/or in the DXE protocol
database (as dictated by the platform's needs in these firmware phases)
implies that the platform provides the operating system with a Device
Tree-based hardware description. This is not necessarily exclusive with
other types of hardware description (for example, an ACPI-based one).

A platform PEIM and/or DXE driver is supposed to produce a single instance
of the PPI and/or protocol (with NULL contents), if appropriate. The
decision to produce the PPI and/or protocol is platform specific; for
example, in the DXE phase, it could depend on an HII checkbox / underlying
non-volatile UEFI variable.

In the DXE phase, the protocol is meant to be consumed by the platform
driver that
- owns the Device Tree description of the hardware, and
- is responsible for installing it as a system configuration table.

Said FDT-owner driver can wait for the protocol via DEPEX or protocol
notify.

Because this GUID is not standard, it is prefixed with EDKII / Edkii, as
seen elsewhere (for example in MdeModulePkg and SecurityPkg).

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:
    v4:
    - pick up Ard's R-b
    
    v3:
    - move GUID from ArmPkg to EmbeddedPkg [Leif]
    - apply the protocol -> generic GUID changes to naming, comments, and
      the commit message, that were suggested by Star for the MdeModulePkg /
      ACPI counterpart

 EmbeddedPkg/EmbeddedPkg.dec                      |  3 ++
 EmbeddedPkg/Include/Guid/PlatformHasDeviceTree.h | 35 ++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/EmbeddedPkg/EmbeddedPkg.dec b/EmbeddedPkg/EmbeddedPkg.dec
index d078bf794a79..29736fb4a71d 100644
--- a/EmbeddedPkg/EmbeddedPkg.dec
+++ b/EmbeddedPkg/EmbeddedPkg.dec
@@ -59,6 +59,9 @@ [Guids.common]
   ## Include/Guid/PlatformHasAcpi.h
   gEdkiiPlatformHasAcpiGuid = { 0xf0966b41, 0xc23f, 0x41b9, { 0x96, 0x04, 0x0f, 0xf7, 0xe1, 0x11, 0x96, 0x5a } }
 
+  ## Include/Guid/PlatformHasDeviceTree.h
+  gEdkiiPlatformHasDeviceTreeGuid = { 0x7ebb920d, 0x1aaf, 0x46d9, { 0xb2, 0xaf, 0x54, 0x1e, 0x1d, 0xce, 0x14, 0x8b } }
+
 [Protocols.common]
   gHardwareInterruptProtocolGuid =  { 0x2890B3EA, 0x053D, 0x1643, { 0xAD, 0x0C, 0xD6, 0x48, 0x08, 0xDA, 0x3F, 0xF1 } }
   gEfiDebugSupportPeriodicCallbackProtocolGuid = { 0x9546e07c, 0x2cbb, 0x4c88, { 0x98, 0x6c, 0xcd, 0x34, 0x10, 0x86, 0xf0, 0x44 } }
diff --git a/EmbeddedPkg/Include/Guid/PlatformHasDeviceTree.h b/EmbeddedPkg/Include/Guid/PlatformHasDeviceTree.h
new file mode 100644
index 000000000000..a9bc51270cda
--- /dev/null
+++ b/EmbeddedPkg/Include/Guid/PlatformHasDeviceTree.h
@@ -0,0 +1,35 @@
+/** @file
+  EDKII Platform Has Device Tree GUID
+
+  A NULL protocol instance with this GUID in the DXE protocol database, and/or
+  a NULL PPI with this GUID in the PPI database, implies that the platform
+  provides the operating system with a Device Tree-based hardware description.
+  Note that this is not necessarily exclusive with different kinds of hardware
+  description (for example, an ACPI-based one). A platform driver and/or PEIM
+  is supposed to produce a single instance of the protocol and/or PPI (with
+  NULL contents), if appropriate.
+
+  Copyright (C) 2017, Red Hat, Inc.
+
+  This program and the accompanying materials are licensed and made available
+  under the terms and conditions of the BSD License that accompanies this
+  distribution. The full text of the license may be found at
+  http://opensource.org/licenses/bsd-license.php.
+
+  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, WITHOUT
+  WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+**/
+
+
+#ifndef __EDKII_PLATFORM_HAS_DEVICE_TREE_H__
+#define __EDKII_PLATFORM_HAS_DEVICE_TREE_H__
+
+#define EDKII_PLATFORM_HAS_DEVICE_TREE_GUID \
+  { \
+    0x7ebb920d, 0x1aaf, 0x46d9, \
+    { 0xb2, 0xaf, 0x54, 0x1e, 0x1d, 0xce, 0x14, 0x8b } \
+  }
+
+extern EFI_GUID gEdkiiPlatformHasDeviceTreeGuid;
+
+#endif
-- 
2.9.3


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