Re: [PATCH 2/4] target/arm: Abstract the generic timer frequency

[Cédric Le Goater]

On 28/11/2019 06:45, Andrew Jeffery wrote:
> Prepare for SoCs such as the ASPEED AST2600 whose firmware configures
> CNTFRQ to values significantly larger than the static 62.5MHz value
> currently derived from GTIMER_SCALE. As the OS potentially derives its
> timer periods from the CNTFRQ value the lack of support for running
> QEMUTimers at the appropriate rate leads to sticky behaviour in the
> guest.
> 
> Substitute the GTIMER_SCALE constant with use of a helper to derive the
> period from gt_cntfrq stored in struct ARMCPU. Initially set gt_cntfrq
> to the frequency associated with GTIMER_SCALE so current behaviour is
> maintained.
> 
> Signed-off-by: Andrew Jeffery <address@hidden>
> ---
>  target/arm/cpu.c    |  2 ++
>  target/arm/cpu.h    | 10 ++++++++++
>  target/arm/helper.c | 10 +++++++---
>  3 files changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
> index 7a4ac9339bf9..5698a74061bb 100644
> --- a/target/arm/cpu.c
> +++ b/target/arm/cpu.c
> @@ -974,6 +974,8 @@ static void arm_cpu_initfn(Object *obj)
>      if (tcg_enabled()) {
>          cpu->psci_version = 2; /* TCG implements PSCI 0.2 */
>      }
> +
> +    cpu->gt_cntfrq = NANOSECONDS_PER_SECOND / GTIMER_SCALE;
>  }
>  
>  static Property arm_cpu_reset_cbar_property =
> diff --git a/target/arm/cpu.h b/target/arm/cpu.h
> index 83a809d4bac4..666c03871fdf 100644
> --- a/target/arm/cpu.h
> +++ b/target/arm/cpu.h
> @@ -932,8 +932,18 @@ struct ARMCPU {
>       */
>      DECLARE_BITMAP(sve_vq_map, ARM_MAX_VQ);
>      DECLARE_BITMAP(sve_vq_init, ARM_MAX_VQ);
> +
> +    /* Generic timer counter frequency, in Hz */
> +    uint64_t gt_cntfrq;
>  };
>  
> +static inline unsigned int gt_cntfrq_period_ns(ARMCPU *cpu)
> +{
> +    /* XXX: Could include qemu/timer.h to get NANOSECONDS_PER_SECOND? */
> +    const unsigned int ns_per_s = 1000 * 1000 * 1000;
> +    return ns_per_s > cpu->gt_cntfrq ? ns_per_s / cpu->gt_cntfrq : 1;
> +}

Are you inlining this helper for performance reasons ? 

C. 


>  void arm_cpu_post_init(Object *obj);
>  
>  uint64_t arm_cpu_mp_affinity(int idx, uint8_t clustersz);
> diff --git a/target/arm/helper.c b/target/arm/helper.c
> index 65c4441a3896..1cc0551081a0 100644
> --- a/target/arm/helper.c
> +++ b/target/arm/helper.c
> @@ -2409,7 +2409,9 @@ static CPAccessResult gt_stimer_access(CPUARMState *env,
>  
>  static uint64_t gt_get_countervalue(CPUARMState *env)
>  {
> -    return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) / GTIMER_SCALE;
> +    ARMCPU *cpu = env_archcpu(env);
> +
> +    return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) / gt_cntfrq_period_ns(cpu);
>  }
>  
>  static void gt_recalc_timer(ARMCPU *cpu, int timeridx)
> @@ -2445,7 +2447,7 @@ static void gt_recalc_timer(ARMCPU *cpu, int timeridx)
>           * set the timer for as far in the future as possible. When the
>           * timer expires we will reset the timer for any remaining period.
>           */
> -        if (nexttick > INT64_MAX / GTIMER_SCALE) {
> +        if (nexttick > INT64_MAX / gt_cntfrq_period_ns(cpu)) {
>              timer_mod_ns(cpu->gt_timer[timeridx], INT64_MAX);
>          } else {
>              timer_mod(cpu->gt_timer[timeridx], nexttick);
> @@ -2874,11 +2876,13 @@ static const ARMCPRegInfo generic_timer_cp_reginfo[] 
> = {
>  
>  static uint64_t gt_virt_cnt_read(CPUARMState *env, const ARMCPRegInfo *ri)
>  {
> +    ARMCPU *cpu = env_archcpu(env);
> +
>      /* Currently we have no support for QEMUTimer in linux-user so we
>       * can't call gt_get_countervalue(env), instead we directly
>       * call the lower level functions.
>       */
> -    return cpu_get_clock() / GTIMER_SCALE;
> +    return cpu_get_clock() / gt_cntfrq_period(cpu);
>  }
>  
>  static const ARMCPRegInfo generic_timer_cp_reginfo[] = {
>