[PATCH v2 4/5] ArmPlatformPkg/HdLcdArmVExpressLib: 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/HdLcdArmVExpressLib/HdLcdArmVExpress.c      | 12 ++++--------
 ArmPlatformPkg/ArmVExpressPkg/Library/HdLcdArmVExpressLib/HdLcdArmVExpressLib.inf |  3 ++-
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/ArmPlatformPkg/ArmVExpressPkg/Library/HdLcdArmVExpressLib/HdLcdArmVExpress.c b/ArmPlatformPkg/ArmVExpressPkg/Library/HdLcdArmVExpressLib/HdLcdArmVExpress.c
index 67b2f14beee3..b1106ee19b98 100644
--- a/ArmPlatformPkg/ArmVExpressPkg/Library/HdLcdArmVExpressLib/HdLcdArmVExpress.c
+++ b/ArmPlatformPkg/ArmVExpressPkg/Library/HdLcdArmVExpressLib/HdLcdArmVExpress.c
@@ -18,11 +18,11 @@
 #include <Library/IoLib.h>
 #include <Library/PcdLib.h>
 #include <Library/DebugLib.h>
+#include <Library/DxeServicesTableLib.h>
 #include <Library/LcdPlatformLib.h>
 #include <Library/MemoryAllocationLib.h>
 #include <Library/UefiBootServicesTableLib.h>
 
-#include <Protocol/Cpu.h>
 #include <Protocol/EdidDiscovered.h>
 #include <Protocol/EdidActive.h>
 
@@ -119,7 +119,6 @@ LcdPlatformGetVram (
   )
 {
   EFI_STATUS              Status;
-  EFI_CPU_ARCH_PROTOCOL  *Cpu;
   EFI_ALLOCATE_TYPE       AllocationType;
 
   // Set the vram size
@@ -138,12 +137,9 @@ 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-cacheable. The VRAM is inside the DRAM, which is cacheable.
-  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/HdLcdArmVExpressLib/HdLcdArmVExpressLib.inf b/ArmPlatformPkg/ArmVExpressPkg/Library/HdLcdArmVExpressLib/HdLcdArmVExpressLib.inf
index 780724737929..dff17e86fd3e 100644
--- a/ArmPlatformPkg/ArmVExpressPkg/Library/HdLcdArmVExpressLib/HdLcdArmVExpressLib.inf
+++ b/ArmPlatformPkg/ArmVExpressPkg/Library/HdLcdArmVExpressLib/HdLcdArmVExpressLib.inf
@@ -32,8 +32,9 @@ [Packages]
   ArmPlatformPkg/ArmVExpressPkg/ArmVExpressPkg.dec
 
 [LibraryClasses]
-  BaseLib
   ArmPlatformSysConfigLib
+  BaseLib
+  DxeServicesTableLib
 
 [Protocols]
   gEfiEdidDiscoveredProtocolGuid                # Produced
-- 
2.9.3