The TimerDxe implementation doesn't account for the physical time passed due to timer handler execution or (perhaps even more importantly) time spent with interrupts masked.
Other implementations (e.g. like the Arm one) do. If the timer tick is always incremented at a fixed rate, then you can slow down UEFI's perception of time by running long sections of code in a critical section. Cc: Sunil V L <[email protected]> Cc: Daniel Schaefer <[email protected]> Signed-off-by: Andrei Warkentin <[email protected]> --- UefiCpuPkg/CpuTimerDxeRiscV64/Timer.c | 31 ++++++++++++-------- 1 file changed, 18 insertions(+), 13 deletions(-) diff --git a/UefiCpuPkg/CpuTimerDxeRiscV64/Timer.c b/UefiCpuPkg/CpuTimerDxeRiscV64/Timer.c index 0ecefddf1f18..f65c64c296cd 100644 --- a/UefiCpuPkg/CpuTimerDxeRiscV64/Timer.c +++ b/UefiCpuPkg/CpuTimerDxeRiscV64/Timer.c @@ -41,6 +41,7 @@ STATIC EFI_TIMER_NOTIFY mTimerNotifyFunction; // The current period of the timer interrupt // STATIC UINT64 mTimerPeriod = 0; +STATIC UINT64 mLastPeriodStart = 0; /** Timer Interrupt Handler. @@ -55,26 +56,32 @@ TimerInterruptHandler ( IN EFI_SYSTEM_CONTEXT SystemContext ) { - EFI_TPL OriginalTPL; - UINT64 RiscvTimer; + EFI_TPL OriginalTPL; + UINT64 PeriodStart = RiscVReadTimer (); OriginalTPL = gBS->RaiseTPL (TPL_HIGH_LEVEL); if (mTimerNotifyFunction != NULL) { - mTimerNotifyFunction (mTimerPeriod); + // + // For any number of reasons, the ticks could be coming + // in slower than mTimerPeriod. For example, some code + // is doing a *lot* of stuff inside an EFI_TPL_HIGH + // critical section, and this should not cause the EFI + // time to increment slower. So when we take an interrupt, + // account for the actual time passed. + // + mTimerNotifyFunction (PeriodStart - mLastPeriodStart); } - RiscVDisableTimerInterrupt (); // Disable SMode timer int - RiscVClearPendingTimerInterrupt (); if (mTimerPeriod == 0) { + RiscVDisableTimerInterrupt (); gBS->RestoreTPL (OriginalTPL); - RiscVDisableTimerInterrupt (); // Disable SMode timer int return; } - RiscvTimer = RiscVReadTimer (); - SbiSetTimer (RiscvTimer += mTimerPeriod); + mLastPeriodStart = PeriodStart; + SbiSetTimer (PeriodStart += mTimerPeriod); + RiscVEnableTimerInterrupt (); // enable SMode timer int gBS->RestoreTPL (OriginalTPL); - RiscVEnableTimerInterrupt (); // enable SMode timer int } /** @@ -154,8 +161,6 @@ TimerDriverSetTimerPeriod ( IN UINT64 TimerPeriod ) { - UINT64 RiscvTimer; - DEBUG ((DEBUG_INFO, "TimerDriverSetTimerPeriod(0x%lx)\n", TimerPeriod)); if (TimerPeriod == 0) { @@ -165,8 +170,8 @@ TimerDriverSetTimerPeriod ( } mTimerPeriod = TimerPeriod / 10; // convert unit from 100ns to 1us - RiscvTimer = RiscVReadTimer (); - SbiSetTimer (RiscvTimer + mTimerPeriod); + mLastPeriodStart = RiscVReadTimer (); + SbiSetTimer (mLastPeriodStart + mTimerPeriod); mCpu->EnableInterrupt (mCpu); RiscVEnableTimerInterrupt (); // enable SMode timer int -- 2.25.1 -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#100337): https://edk2.groups.io/g/devel/message/100337 Mute This Topic: https://groups.io/mt/97044196/21656 Group Owner: [email protected] Unsubscribe: https://edk2.groups.io/g/devel/unsub [[email protected]] -=-=-=-=-=-=-=-=-=-=-=-
