[PATCH v2 7/7] OvmfPkg/OvmfXen: Set PcdFSBClock

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

Update gEfiMdePkgTokenSpaceGuid.PcdFSBClock so it can have the correct
value when SecPeiDxeTimerLibCpu start to use it for the APIC timer.

Currently, nothing appear to use the value in PcdFSBClock before
XenPlatformPei had a chance to set it even though TimerLib is included
in modules runned before XenPlatformPei.

XenPlatformPei doesn't use any of the functions that would use that
value. No other modules in the PEI phase seems to use the TimerLib
before PcdFSBClock is set. There are currently two other modules in
the PEI phase that needs the TimerLib:
- S3Resume2Pei, but only because LocalApicLib needs it, but nothing is
  using the value from PcdFSBClock.
- CpuMpPei, but I believe it only runs after XenPlatformPei

Before the PEI phase, there's the SEC phase, and SecMain needs
TimerLib because of LocalApicLib. And it initialise the APIC timers
for the debug agent. But I don't think any of the DebugLib that
OvmfXen could use are actually using the *Delay functions in TimerLib,
and so would not use the value from PcdFSBClock which would be
uninitialised.

A simple runtime test showed that TimerLib doesn't use PcdFSBClock
value before it is set.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2490
Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
Reviewed-by: Laszlo Ersek <lersek@xxxxxxxxxx>
---

Notes:
    v2:
    - keep the default value of PcdFSBClock because that is part of the syntax.

 OvmfPkg/OvmfXen.dsc                       | 4 +---
 OvmfPkg/XenPlatformPei/XenPlatformPei.inf | 1 +
 OvmfPkg/XenPlatformPei/Xen.c              | 4 ++++
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/OvmfPkg/OvmfXen.dsc b/OvmfPkg/OvmfXen.dsc
index 507029404f0b..faf3930ace04 100644
--- a/OvmfPkg/OvmfXen.dsc
+++ b/OvmfPkg/OvmfXen.dsc
@@ -442,9 +442,6 @@ [PcdsFixedAtBuild]
   # Point to the MdeModulePkg/Application/UiApp/UiApp.inf
   gEfiMdeModulePkgTokenSpaceGuid.PcdBootManagerMenuFile|{ 0x21, 0xaa, 0x2c, 
0x46, 0x14, 0x76, 0x03, 0x45, 0x83, 0x6e, 0x8a, 0xb6, 0xf4, 0x66, 0x23, 0x31 }
 
-  ## Xen vlapic's frequence is 100 MHz
-  gEfiMdePkgTokenSpaceGuid.PcdFSBClock|100000000
-
   # We populate DXE IPL tables with 1G pages preferably on Xen
   gEfiMdeModulePkgTokenSpaceGuid.PcdUse1GPageTable|TRUE
 
@@ -471,6 +468,7 @@ [PcdsDynamicDefault]
   gUefiOvmfPkgTokenSpaceGuid.PcdPciMmio64Base|0x0
   gUefiOvmfPkgTokenSpaceGuid.PcdPciMmio64Size|0x800000000
 
+  gEfiMdePkgTokenSpaceGuid.PcdFSBClock|100000000
   gEfiMdePkgTokenSpaceGuid.PcdPlatformBootTimeOut|0
 
   # Set video resolution for text setup.
diff --git a/OvmfPkg/XenPlatformPei/XenPlatformPei.inf 
b/OvmfPkg/XenPlatformPei/XenPlatformPei.inf
index 5732d2188871..87dd4b24679a 100644
--- a/OvmfPkg/XenPlatformPei/XenPlatformPei.inf
+++ b/OvmfPkg/XenPlatformPei/XenPlatformPei.inf
@@ -85,6 +85,7 @@ [Pcd]
   gEfiMdeModulePkgTokenSpaceGuid.PcdDxeIplSwitchToLongMode
   gEfiMdeModulePkgTokenSpaceGuid.PcdUse1GPageTable
   gEfiMdeModulePkgTokenSpaceGuid.PcdPteMemoryEncryptionAddressOrMask
+  gEfiMdePkgTokenSpaceGuid.PcdFSBClock
   gEfiSecurityPkgTokenSpaceGuid.PcdOptionRomImageVerificationPolicy
   gUefiCpuPkgTokenSpaceGuid.PcdCpuLocalApicBaseAddress
 
diff --git a/OvmfPkg/XenPlatformPei/Xen.c b/OvmfPkg/XenPlatformPei/Xen.c
index 7524aaa11a29..a29b4e04086e 100644
--- a/OvmfPkg/XenPlatformPei/Xen.c
+++ b/OvmfPkg/XenPlatformPei/Xen.c
@@ -632,5 +632,9 @@ CalibrateLapicTimer (
   Freq = DivU64x64Remainder (Dividend, TscTick2 - TscTick, NULL);
   DEBUG ((DEBUG_INFO, "APIC Freq % 8lu Hz\n", Freq));
 
+  ASSERT (Freq <= MAX_UINT32);
+  Status = PcdSet32S (PcdFSBClock, Freq);
+  ASSERT_RETURN_ERROR (Status);
+
   UnmapXenPage (SharedInfo);
 }
-- 
Anthony PERARD