[edk2-devel] [PATCH V5 32/33] UefiCpuPkg: Setting initial-count register as the last step

[Min Xu]

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3711

Per SDM, changing the mode of APIC timer (from one-shot to periodic or
vice versa) by writing to the timer LVT entry does not start the timer.
To start the timer, it is necessary to write to the initial-count
register.

If initial-count is wrote before mode change, it's possible that timer
expired before the mode change. Thus failing the periodic mode.

Cc: Jiewen Yao <jiewen.yao at intel.com>
Cc: Gerd Hoffmann <kraxel at redhat.com>
Cc: Anthony Perard <anthony.perard at citrix.com>
Cc: Julien Grall <julien at xen.org>
Cc: Eric Dong <eric.dong at intel.com>
Cc: Ray Ni <ray.ni at intel.com>
Acked-by: Gerd Hoffmann <kraxel at redhat.com>
Signed-off-by: Min Xu <min.m.xu at intel.com>
---
 .../Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c    | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c b/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
index 2d17177df12b..f26d9c93894f 100644
--- a/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
+++ b/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
@@ -967,11 +967,6 @@ 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));
@@ -996,6 +991,11 @@ 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);
 }
 
 /**
-- 
2.29.2.windows.2



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