[PATCH v2 5/5] ArmPlatformPkg/PL111LcdArmVExpressLib: use write-combine mapping for VRAM

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

Replace the uncached memory mapping of the framebuffer with a write-
combining one. This improves performance, and avoids issues with
unaligned accesses and DC ZVA instructions performed by the accelerated
memcpy/memset routines.

Instead of manipulating the memory attributes directly, use the
SetMemorySpaceAttributes() DXE services, which validates the attributes
against the capabilities of the region before making the actual change.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 ArmPlatformPkg/ArmVExpressPkg/Library/PL111LcdArmVExpressLib/PL111LcdArmVExpress.c      | 12 ++++--------
 ArmPlatformPkg/ArmVExpressPkg/Library/PL111LcdArmVExpressLib/PL111LcdArmVExpressLib.inf |  3 ++-
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/ArmPlatformPkg/ArmVExpressPkg/Library/PL111LcdArmVExpressLib/PL111LcdArmVExpress.c b/ArmPlatformPkg/ArmVExpressPkg/Library/PL111LcdArmVExpressLib/PL111LcdArmVExpress.c
index a8125e81daac..3f3ceb3d2fa8 100644
--- a/ArmPlatformPkg/ArmVExpressPkg/Library/PL111LcdArmVExpressLib/PL111LcdArmVExpress.c
+++ b/ArmPlatformPkg/ArmVExpressPkg/Library/PL111LcdArmVExpressLib/PL111LcdArmVExpress.c
@@ -17,10 +17,10 @@
 #include <Library/IoLib.h>
 #include <Library/PcdLib.h>
 #include <Library/DebugLib.h>
+#include <Library/DxeServicesTableLib.h>
 #include <Library/LcdPlatformLib.h>
 #include <Library/UefiBootServicesTableLib.h>
 
-#include <Protocol/Cpu.h>
 #include <Protocol/EdidDiscovered.h>
 #include <Protocol/EdidActive.h>
 
@@ -165,7 +165,6 @@ LcdPlatformGetVram (
   )
 {
   EFI_STATUS              Status;
-  EFI_CPU_ARCH_PROTOCOL  *Cpu;
 
   Status = EFI_SUCCESS;
 
@@ -187,12 +186,9 @@ LcdPlatformGetVram (
       return Status;
     }
 
-    // Ensure the Cpu architectural protocol is already installed
-    Status = gBS->LocateProtocol (&gEfiCpuArchProtocolGuid, NULL, (VOID **)&Cpu);
-    ASSERT_EFI_ERROR(Status);
-
-    // Mark the VRAM as un-cachable. The VRAM is inside the DRAM, which is cachable.
-    Status = Cpu->SetMemoryAttributes(Cpu, *VramBaseAddress, *VramSize, EFI_MEMORY_UC);
+    // Mark the VRAM as write-combining. The VRAM is inside the DRAM, which is cacheable.
+    Status = gDS->SetMemorySpaceAttributes (*VramBaseAddress, *VramSize,
+                    EFI_MEMORY_WC);
     ASSERT_EFI_ERROR(Status);
     if (EFI_ERROR(Status)) {
       gBS->FreePages (*VramBaseAddress, EFI_SIZE_TO_PAGES(*VramSize));
diff --git a/ArmPlatformPkg/ArmVExpressPkg/Library/PL111LcdArmVExpressLib/PL111LcdArmVExpressLib.inf b/ArmPlatformPkg/ArmVExpressPkg/Library/PL111LcdArmVExpressLib/PL111LcdArmVExpressLib.inf
index d1978e7110d5..658558ab1523 100644
--- a/ArmPlatformPkg/ArmVExpressPkg/Library/PL111LcdArmVExpressLib/PL111LcdArmVExpressLib.inf
+++ b/ArmPlatformPkg/ArmVExpressPkg/Library/PL111LcdArmVExpressLib/PL111LcdArmVExpressLib.inf
@@ -31,8 +31,9 @@ [Packages]
   ArmPlatformPkg/ArmPlatformPkg.dec
 
 [LibraryClasses]
-  BaseLib
   ArmPlatformSysConfigLib
+  BaseLib
+  DxeServicesTableLib
 
 [Protocols]
   gEfiEdidDiscoveredProtocolGuid                # Produced
-- 
2.9.3