[PATCH 4/7] ArmPlatformPkg/PrePeiCore: permit entry with the MMU enabled

["Ard Biesheuvel" <ardb@kernel.org>]

Some platforms may set up a preliminary ID map in flash and enter EFI
with the MMU and caches enabled, as this removes a lot of the complexity
around cache coherency. Let's take this into account, and avoid touching
the MMU controls or perform cache invalidation when the MMU is enabled
at entry.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 ArmPlatformPkg/PrePeiCore/PrePeiCore.c | 22 +++++++++++---------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/ArmPlatformPkg/PrePeiCore/PrePeiCore.c b/ArmPlatformPkg/PrePeiCore/PrePeiCore.c
index 6dd9bcdea24f..d56918365f71 100644
--- a/ArmPlatformPkg/PrePeiCore/PrePeiCore.c
+++ b/ArmPlatformPkg/PrePeiCore/PrePeiCore.c
@@ -58,17 +58,19 @@ CEntryPoint (
   IN  EFI_PEI_CORE_ENTRY_POINT  PeiCoreEntryPoint
   )
 {
-  // Data Cache enabled on Primary core when MMU is enabled.
-  ArmDisableDataCache ();
-  // Invalidate instruction cache
-  ArmInvalidateInstructionCache ();
-  // Enable Instruction Caches on all cores.
-  ArmEnableInstructionCache ();
+  if (!ArmMmuEnabled ()) {
+    // Data Cache enabled on Primary core when MMU is enabled.
+    ArmDisableDataCache ();
+    // Invalidate instruction cache
+    ArmInvalidateInstructionCache ();
+    // Enable Instruction Caches on all cores.
+    ArmEnableInstructionCache ();
 
-  InvalidateDataCacheRange (
-    (VOID *)(UINTN)PcdGet64 (PcdCPUCoresStackBase),
-    PcdGet32 (PcdCPUCorePrimaryStackSize)
-    );
+    InvalidateDataCacheRange (
+      (VOID *)(UINTN)PcdGet64 (PcdCPUCoresStackBase),
+      PcdGet32 (PcdCPUCorePrimaryStackSize)
+      );
+  }
 
   //
   // Note: Doesn't have to Enable CPU interface in non-secure world,
-- 
2.35.1