[PATCH] EmbeddedPkg/DtPlatformDxe: remove /chosen/stdout-path on GOP registration

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

The presence of a /chosen/stdout-path property will force Linux to use
the serial port as the primary console, even if a graphical console is
available as well. But the presence of the Graphics Output Protocol (GOP)
is a strong indication that the user may prefer to use his keyboard and
mouse rather than his terminal emulator to interact with the system, so
let's remove /chosen/stdout-path as soon as a GOP instance is registered.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 EmbeddedPkg/Drivers/DtPlatformDxe/DtPlatformDxe.c   | 41 ++++++++++++++++++++
 EmbeddedPkg/Drivers/DtPlatformDxe/DtPlatformDxe.inf |  4 ++
 2 files changed, 45 insertions(+)

diff --git a/EmbeddedPkg/Drivers/DtPlatformDxe/DtPlatformDxe.c b/EmbeddedPkg/Drivers/DtPlatformDxe/DtPlatformDxe.c
index 1014be2281d4..4f9ac8090fac 100644
--- a/EmbeddedPkg/Drivers/DtPlatformDxe/DtPlatformDxe.c
+++ b/EmbeddedPkg/Drivers/DtPlatformDxe/DtPlatformDxe.c
@@ -12,6 +12,7 @@
 *
 **/
 
+#include <libfdt.h>
 #include <Library/BaseLib.h>
 #include <Library/DebugLib.h>
 #include <Library/DevicePathLib.h>
@@ -54,6 +55,9 @@ STATIC HII_VENDOR_DEVICE_PATH     mDtPlatformDxeVendorDevicePath = {
   }
 };
 
+STATIC EFI_EVENT                  mRegisterGopEvent;
+STATIC VOID                       *mGopRegistration;
+
 STATIC
 EFI_STATUS
 InstallHiiPages (
@@ -89,6 +93,32 @@ InstallHiiPages (
   return EFI_SUCCESS;
 }
 
+STATIC
+VOID
+OnRegisterGop (
+  IN EFI_EVENT  Event,
+  IN VOID       *Dtb
+  )
+{
+  INT32     Node;
+  INT32     Error;
+
+  DEBUG ((DEBUG_INFO,
+    "%a: a GOP has been registered, removing /chosen/stdout-path from DT\n",
+    __FUNCTION__));
+
+  Node = fdt_path_offset (Dtb, "/chosen");
+  if (Node < 0) {
+    return;
+  }
+
+  Error = fdt_delprop (Dtb, Node, "stdout-path");
+  if (Error) {
+    DEBUG ((DEBUG_INFO, "%a: Failed to delete 'stdout-path' property: %a\n",
+      __FUNCTION__, fdt_strerror (Error)));
+  }
+}
+
 /**
   The entry point for DtPlatformDxe driver.
 
@@ -181,6 +211,17 @@ DtPlatformDxeEntryPoint (
         __FUNCTION__));
       goto FreeDtb;
     }
+
+    Status = gBS->CreateEvent (EVT_NOTIFY_SIGNAL, TPL_CALLBACK,
+                    OnRegisterGop, Dtb, &mRegisterGopEvent);
+    if (EFI_ERROR (Status)) {
+      DEBUG ((DEBUG_ERROR, "%a: failed to create event - %r\n",
+        __FUNCTION__, Status));
+    }
+
+    Status = gBS->RegisterProtocolNotify (&gEfiGraphicsOutputProtocolGuid,
+                    mRegisterGopEvent, &mGopRegistration);
+    ASSERT_EFI_ERROR (Status);
   } else {
     ASSERT (FALSE);
   }
diff --git a/EmbeddedPkg/Drivers/DtPlatformDxe/DtPlatformDxe.inf b/EmbeddedPkg/Drivers/DtPlatformDxe/DtPlatformDxe.inf
index 45dfd9088bf0..6b331294df8a 100644
--- a/EmbeddedPkg/Drivers/DtPlatformDxe/DtPlatformDxe.inf
+++ b/EmbeddedPkg/Drivers/DtPlatformDxe/DtPlatformDxe.inf
@@ -41,6 +41,7 @@ [LibraryClasses]
   BaseLib
   DebugLib
   DtPlatformDtbLoaderLib
+  FdtLib
   HiiLib
   MemoryAllocationLib
   UefiBootServicesTableLib
@@ -53,6 +54,9 @@ [Guids]
   gEdkiiPlatformHasAcpiGuid
   gFdtTableGuid
 
+[Protocols]
+  gEfiGraphicsOutputProtocolGuid
+
 [Depex]
   gEfiVariableArchProtocolGuid        AND
   gEfiVariableWriteArchProtocolGuid
-- 
2.11.0