[PATCH RFC 10/14] UefiCpuPkg/BaseXApicX2ApicLib: Fix initialisation on my system and ...

[Anthony PERARD <anthony.perard@citrix.com>]

declare more exported function, ReadLocalApicReg and WriteLocalApicReg.

On my system (running OVMF inside a Xen PVH guest), writing the
interrupt information (to XAPIC_LVT_TIMER_OFFSET) would also reset the
init-count register, thus disabling the timer.
---
 UefiCpuPkg/Include/Library/LocalApicLib.h          | 40 ++++++++++++++++++++++
 .../BaseXApicX2ApicLib/BaseXApicX2ApicLib.c        | 10 +++---
 2 files changed, 45 insertions(+), 5 deletions(-)

diff --git a/UefiCpuPkg/Include/Library/LocalApicLib.h b/UefiCpuPkg/Include/Library/LocalApicLib.h
index fc980bc..ab621f2 100644
--- a/UefiCpuPkg/Include/Library/LocalApicLib.h
+++ b/UefiCpuPkg/Include/Library/LocalApicLib.h
@@ -48,6 +48,46 @@ SetLocalApicBaseAddress (
   );
 
 /**
+  Read from a local APIC register.
+
+  This function reads from a local APIC register either in xAPIC or x2APIC mode.
+  It is required that in xAPIC mode wider registers (64-bit or 256-bit) must be
+  accessed using multiple 32-bit loads or stores, so this function only performs
+  32-bit read.
+
+  @param  MmioOffset  The MMIO offset of the local APIC register in xAPIC mode.
+                      It must be 16-byte aligned.
+
+  @return 32-bit      Value read from the register.
+**/
+UINT32
+EFIAPI
+ReadLocalApicReg (
+  IN UINTN  MmioOffset
+  );
+
+/**
+  Write to a local APIC register.
+
+  This function writes to a local APIC register either in xAPIC or x2APIC mode.
+  It is required that in xAPIC mode wider registers (64-bit or 256-bit) must be
+  accessed using multiple 32-bit loads or stores, so this function only performs
+  32-bit write.
+
+  if the register index is invalid or unsupported in current APIC mode, then ASSERT.
+
+  @param  MmioOffset  The MMIO offset of the local APIC register in xAPIC mode.
+                      It must be 16-byte aligned.
+  @param  Value       Value to be written to the register.
+**/
+VOID
+EFIAPI
+WriteLocalApicReg (
+  IN UINTN  MmioOffset,
+  IN UINT32 Value
+  );
+
+/**
   Get the current local APIC mode.
 
   If local APIC is disabled, then ASSERT.
diff --git a/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c b/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
index e690d2a..f84a40a 100644
--- a/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
+++ b/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
@@ -820,11 +820,6 @@ InitializeApicTimer (
   //
   InitializeLocalApicSoftwareEnable (TRUE);
 
-  //
-  // Program init-count register.
-  //
-  WriteLocalApicReg (XAPIC_TIMER_INIT_COUNT_OFFSET, InitCount);
-
   if (DivideValue != 0) {
     ASSERT (DivideValue <= 128);
     ASSERT (DivideValue == GetPowerOfTwo32((UINT32)DivideValue));
@@ -848,6 +843,11 @@ InitializeApicTimer (
   LvtTimer.Bits.Mask = 0;
   LvtTimer.Bits.Vector = Vector;
   WriteLocalApicReg (XAPIC_LVT_TIMER_OFFSET, LvtTimer.Uint32);
+
+  //
+  // Program init-count register.
+  //
+  WriteLocalApicReg (XAPIC_TIMER_INIT_COUNT_OFFSET, InitCount);
 }
 
 /**
-- 
Anthony PERARD