[edk2-devel] [PATCH v2] MdeModulePkg/XhciDxe: Non-zero start/stop values in XhcGetElapsedTicks

["Henz, Patrick" <patrick.henz@hpe.com>]

From: Patrick Henz <patrick.henz@hpe.com>

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=4578

The implementation of XhcGetElapsedTicks did not account for
non-zero start and stop values for the performance counter
timer, potentially resulting in an incorrect elapsed tick
count getting returned to the caller. Account for non-zero
start and stop values when calculating the elapsed tick
count.

Cc: Hao A Wu <hao.a.wu@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Signed-off-by: Patrick Henz <patrick.henz@hpe.com>
Reviewed-by:
---
 MdeModulePkg/Bus/Pci/XhciDxe/Xhci.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/MdeModulePkg/Bus/Pci/XhciDxe/Xhci.c b/MdeModulePkg/Bus/Pci/XhciDxe/Xhci.c
index f4e61d223c..ff641d0130 100644
--- a/MdeModulePkg/Bus/Pci/XhciDxe/Xhci.c
+++ b/MdeModulePkg/Bus/Pci/XhciDxe/Xhci.c
@@ -2389,7 +2389,7 @@ XhcGetElapsedTicks (
     // Counter counts upwards, check for an overflow condition
     //
     if (*PreviousTick > CurrentTick) {
-      Delta = (mXhciPerformanceCounterEndValue - *PreviousTick) + CurrentTick;
+      Delta = (CurrentTick - mXhciPerformanceCounterStartValue) + (mXhciPerformanceCounterEndValue - *PreviousTick);
     } else {
       Delta = CurrentTick - *PreviousTick;
     }
@@ -2398,7 +2398,7 @@ XhcGetElapsedTicks (
     // Counter counts downwards, check for an underflow condition
     //
     if (*PreviousTick < CurrentTick) {
-      Delta = (mXhciPerformanceCounterStartValue - CurrentTick) + *PreviousTick;
+      Delta = (mXhciPerformanceCounterStartValue - CurrentTick) + (*PreviousTick - mXhciPerformanceCounterEndValue);
     } else {
       Delta = *PreviousTick - CurrentTick;
     }
-- 
2.34.1