[PATCH v3 04/12] MdeModulePkg: introduce EDKII Platform Has ACPI GUID

[Laszlo Ersek <lersek@redhat.com>]

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 an ACPI-based
hardware description. This is not necessarily exclusive with other types
of hardware description (for example, a Device Tree-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 depended-upon by
"MdeModulePkg/Universal/Acpi/AcpiTableDxe", indirectly:

* In the long term, interested platforms will establish this dependency by
  hooking an (upcoming) NULL-class DepexLib instance into AcpiTableDxe in
  their DSC files, pointing DepexLib's DEPEX through a FixedAtBuild PCD to
  the GUID introduced here. (For the prerequisite BaseTools feature, refer
  to <https://bugzilla.tianocore.org/show_bug.cgi?id=444>).

* In the short term, an interested platform may hook a private NULL-class
  library instance (called e.g. "PlatformHasAcpiLib") into AcpiTableDxe.
  Such a library instance would be a specialization of the above described
  generic DepexLib, with the DEPEX open-coded on the GUID introduced here.

Either way, the platform makes EFI_ACPI_TABLE_PROTOCOL and (if enabled)
EFI_ACPI_SDT_PROTOCOL dependent on the platform's dynamic decision to
produce or not to produce a NULL protocol instance with this GUID.

In turn, other (platform and universal) DXE drivers that produce ACPI
tables will wait for EFI_ACPI_TABLE_PROTOCOL / EFI_ACPI_SDT_PROTOCOL, via
DEPEX, protocol notify, or a simple gBS->LocateProtocol() in a "late
enough" callback (such as Ready To Boot).

Because this GUID is not standard, it is prefixed with EDKII / Edkii, as
seen elsewhere in MdeModulePkg and SecurityPkg. In addition, an effort is
made to avoid the phrase "AcpiPlatform", as that belongs to drivers /
libraries that produce platform specific ACPI content (as opposed to
deciding whether the entire firmware will have access to
EFI_ACPI_TABLE_PROTOCOL, or any similar facilities in the PEI phase).

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Feng Tian <feng.tian@intel.com>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---

Notes:
    v3:
    - rename gEdkiiPlatformHasAcpiProtocolGuid to gEdkiiPlatformHasAcpiGuid
      [Star]
    - update commit message and code comments to reflect possible use as a
      PPI as well [Star]
    - move GUID from ArmPkg to MdeModulePkg [Leif, Ard]
    - split PlatformHasAcpiLib to a separate patch [Star]

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

diff --git a/MdeModulePkg/MdeModulePkg.dec b/MdeModulePkg/MdeModulePkg.dec
index 626e479f5e45..2d94881206d3 100644
--- a/MdeModulePkg/MdeModulePkg.dec
+++ b/MdeModulePkg/MdeModulePkg.dec
@@ -382,6 +382,9 @@ [Guids]
   gEdkiiNonDiscoverableUhciDeviceGuid = { 0xA8CDA0A2, 0x4F37, 0x4A1B, {0x8E, 0x10, 0x8E, 0xF3, 0xCC, 0x3B, 0xF3, 0xA8 } }
   gEdkiiNonDiscoverableXhciDeviceGuid = { 0xB1BE0BC5, 0x6C28, 0x442D, {0xAA, 0x37, 0x15, 0x1B, 0x42, 0x57, 0xBD, 0x78 } }
 
+  ## Include/Guid/PlatformHasAcpi.h
+  gEdkiiPlatformHasAcpiGuid = { 0xf0966b41, 0xc23f, 0x41b9, { 0x96, 0x04, 0x0f, 0xf7, 0xe1, 0x11, 0x96, 0x5a } }
+
 [Ppis]
   ## Include/Ppi/AtaController.h
   gPeiAtaControllerPpiGuid       = { 0xa45e60d1, 0xc719, 0x44aa, { 0xb0, 0x7a, 0xaa, 0x77, 0x7f, 0x85, 0x90, 0x6d }}
diff --git a/MdeModulePkg/Include/Guid/PlatformHasAcpi.h b/MdeModulePkg/Include/Guid/PlatformHasAcpi.h
new file mode 100644
index 000000000000..ad517821375d
--- /dev/null
+++ b/MdeModulePkg/Include/Guid/PlatformHasAcpi.h
@@ -0,0 +1,35 @@
+/** @file
+  EDKII Platform Has ACPI 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 an ACPI-based hardware description. Note
+  that this is not necessarily exclusive with different kinds of hardware
+  description (for example, a Device Tree-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_ACPI_H__
+#define __EDKII_PLATFORM_HAS_ACPI_H__
+
+#define EDKII_PLATFORM_HAS_ACPI_GUID \
+  { \
+    0xf0966b41, 0xc23f, 0x41b9, \
+    { 0x96, 0x04, 0x0f, 0xf7, 0xe1, 0x11, 0x96, 0x5a } \
+  }
+
+extern EFI_GUID gEdkiiPlatformHasAcpiGuid;
+
+#endif
-- 
2.9.3