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

["Henz, Patrick" <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 7a2e32a9dd..6cb97b7452 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 = (mPerformanceCounterEndValue - *PreviousTick) + CurrentTick;
+      Delta = (CurrentTick - mPerformanceCounterStartValue) + (mPerformanceCounterEndValue - *PreviousTick);
     } else {
       Delta = CurrentTick - *PreviousTick;
     }
@@ -2398,7 +2398,7 @@ XhcGetElapsedTicks (
     // Counter counts downwards, check for an underflow condition
     //
     if (*PreviousTick < CurrentTick) {
-      Delta = (mPerformanceCounterStartValue - CurrentTick) + *PreviousTick;
+      Delta = (mPerformanceCounterStartValue - CurrentTick) + (*PreviousTick - mPerformanceCounterEndValue);
     } else {
       Delta = *PreviousTick - CurrentTick;
     }
-- 
2.34.1



-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#110434): https://edk2.groups.io/g/devel/message/110434
Mute This Topic: https://groups.io/mt/102301510/7686176
Group Owner: devel+owner@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [rebecca@openfw.io]
-=-=-=-=-=-=-=-=-=-=-=-