Re: [edk2-devel] [PATCH v2 3/4] UefiCpuPkg/CpuTimerDxeRiscV64: Add support for Sstc

["Laszlo Ersek" <lersek@redhat.com>]

On 1/8/24 12:36, Sunil V L wrote:
> Sstc extension allows to program the timer and receive the interrupt
> without using an SBI call. This reduces the latency to generate the timer
> interrupt. So, detect whether Sstc extension is supported and use the
> stimecmp register directly to program the timer interrupt.
> 
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Rahul Kumar <rahul1.kumar@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Andrei Warkentin <andrei.warkentin@intel.com>
> Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
> ---
>  .../CpuTimerDxeRiscV64/CpuTimerDxeRiscV64.inf |  1 +
>  UefiCpuPkg/CpuTimerDxeRiscV64/Timer.h         |  2 +
>  UefiCpuPkg/CpuTimerDxeRiscV64/Timer.c         | 49 +++++++++++++++++--
>  3 files changed, 49 insertions(+), 3 deletions(-)
> 
> diff --git a/UefiCpuPkg/CpuTimerDxeRiscV64/CpuTimerDxeRiscV64.inf b/UefiCpuPkg/CpuTimerDxeRiscV64/CpuTimerDxeRiscV64.inf
> index aba660186dc0..f2a2cf12caef 100644
> --- a/UefiCpuPkg/CpuTimerDxeRiscV64/CpuTimerDxeRiscV64.inf
> +++ b/UefiCpuPkg/CpuTimerDxeRiscV64/CpuTimerDxeRiscV64.inf
> @@ -41,6 +41,7 @@ [Sources.RISCV64]
>    Timer.c
>  
>  [Pcd]
> +  gEfiMdePkgTokenSpaceGuid.PcdRiscVFeatureOverride           ## CONSUMES
>    gUefiCpuPkgTokenSpaceGuid.PcdCpuCoreCrystalClockFrequency  ## CONSUMES
>  
>  [Protocols]
> diff --git a/UefiCpuPkg/CpuTimerDxeRiscV64/Timer.h b/UefiCpuPkg/CpuTimerDxeRiscV64/Timer.h
> index 9b3542230cb5..067bbd29f377 100644
> --- a/UefiCpuPkg/CpuTimerDxeRiscV64/Timer.h
> +++ b/UefiCpuPkg/CpuTimerDxeRiscV64/Timer.h
> @@ -26,6 +26,8 @@
>  //
>  #define DEFAULT_TIMER_TICK_DURATION  100000
>  
> +#define RISCV_CPU_FEATURE_SSTC_BITMASK  BIT1
> +
>  extern VOID
>  RiscvSetTimerPeriod (
>    UINT32  TimerPeriod
> diff --git a/UefiCpuPkg/CpuTimerDxeRiscV64/Timer.c b/UefiCpuPkg/CpuTimerDxeRiscV64/Timer.c
> index 30e48061cd06..216f48a52931 100644
> --- a/UefiCpuPkg/CpuTimerDxeRiscV64/Timer.c
> +++ b/UefiCpuPkg/CpuTimerDxeRiscV64/Timer.c
> @@ -44,6 +44,45 @@ STATIC EFI_TIMER_NOTIFY  mTimerNotifyFunction;
>  STATIC UINT64  mTimerPeriod     = 0;
>  STATIC UINT64  mLastPeriodStart = 0;
>  
> +//
> +// Sstc support
> +//
> +STATIC BOOLEAN  mSstcEnabled = FALSE;
> +
> +/**
> +  Program the timer.
> +
> +  Program either using stimecmp (when Sstc extension is enabled) or using SBI
> +  TIME call.
> +
> +  @param NextValue             Core tick value the timer should expire.
> +**/
> +STATIC
> +VOID
> +RiscVProgramTimer (
> +  UINT64  NextValue
> +  )
> +{
> +  if (mSstcEnabled) {
> +    RiscVSetSupervisorTimeCompareRegister (NextValue);
> +  } else {
> +    SbiSetTimer (NextValue);
> +  }
> +}
> +
> +/**
> +  Check whether Sstc is enabled in PCD.
> +
> +**/
> +STATIC
> +BOOLEAN
> +RiscVIsSstcEnabled (
> +  VOID
> +  )
> +{
> +  return ((PcdGet64 (PcdRiscVFeatureOverride) & RISCV_CPU_FEATURE_SSTC_BITMASK) != 0);
> +}
> +
>  /**
>    Timer Interrupt Handler.
>  
> @@ -94,7 +133,7 @@ TimerInterruptHandler (
>                           ),
>                         1000000u
>                         );  // convert to tick
> -  SbiSetTimer (PeriodStart);
> +  RiscVProgramTimer (PeriodStart);
>    RiscVEnableTimerInterrupt (); // enable SMode timer int
>    gBS->RestoreTPL (OriginalTPL);
>  }
> @@ -197,8 +236,7 @@ TimerDriverSetTimerPeriod (
>                           ),
>                         1000000u
>                         ); // convert to tick
> -  SbiSetTimer (PeriodStart);
> -
> +  RiscVProgramTimer (PeriodStart);
>    mCpu->EnableInterrupt (mCpu);
>    RiscVEnableTimerInterrupt (); // enable SMode timer int
>    return EFI_SUCCESS;
> @@ -282,6 +320,11 @@ TimerDriverInitialize (
>    //
>    mTimerNotifyFunction = NULL;
>  
> +  if (RiscVIsSstcEnabled ()) {
> +    mSstcEnabled = TRUE;
> +    DEBUG ((DEBUG_INFO, "TimerDriverInitialize: Timer interrupt is via Sstc extension\n"));
> +  }
> +
>    //
>    // Make sure the Timer Architectural Protocol is not already installed in the system
>    //

Reviewed-by: Laszlo Ersek <lersek@redhat.com>



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