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

[Peter Maydell <peter.maydell@linaro.org>]

On Thu, 28 Nov 2019 at 05:44, Andrew Jeffery <andrew@aj.id.au> 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 <andrew@aj.id.au>

> +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;
> +}

This function is named gt_cntfrq_period_ns()...

>  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);
>  }

...but here we call gt_cntfrq_period(), which doesn't exist,
and indeed at least one of the patchew build systems reported
it as a compile failure.

thanks
-- PMM