Re: [PATCH v2 06/18] arm64: arch_timer: Add infrastructure for multiple erratum detection methods

[dann frazier <dann.frazier@canonical.com>]

On Mon, Mar 20, 2017 at 11:48 AM, Marc Zyngier <marc.zyngier@arm.com> wrote:
> We're currently stuck with DT when it comes to handling errata, which
> is pretty restrictive. In order to make things more flexible, let's
> introduce an infrastructure that could support alternative discovery
> methods. No change in functionality.
>
> Reviewed-by: Hanjun Guo <hanjun.guo@linaro.org>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  arch/arm64/include/asm/arch_timer.h  |  7 +++-
>  drivers/clocksource/arm_arch_timer.c | 80 +++++++++++++++++++++++++++++++-----
>  2 files changed, 75 insertions(+), 12 deletions(-)
>
> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
> index b4b34004a21e..5cd964e90d11 100644
> --- a/arch/arm64/include/asm/arch_timer.h
> +++ b/arch/arm64/include/asm/arch_timer.h
> @@ -37,9 +37,14 @@ extern struct static_key_false arch_timer_read_ool_enabled;
>  #define needs_unstable_timer_counter_workaround()  false
>  #endif
>
> +enum arch_timer_erratum_match_type {
> +       ate_match_dt,
> +};
>
>  struct arch_timer_erratum_workaround {
> -       const char *id;         /* Indicate the Erratum ID */
> +       enum arch_timer_erratum_match_type match_type;
> +       const void *id;
> +       const char *desc;
>         u32 (*read_cntp_tval_el0)(void);
>         u32 (*read_cntv_tval_el0)(void);
>         u64 (*read_cntvct_el0)(void);
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 7a8a4117f123..6a0f0e161a0f 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -182,7 +182,9 @@ EXPORT_SYMBOL_GPL(arch_timer_read_ool_enabled);
>  static const struct arch_timer_erratum_workaround ool_workarounds[] = {
>  #ifdef CONFIG_FSL_ERRATUM_A008585
>         {
> +               .match_type = ate_match_dt,
>                 .id = "fsl,erratum-a008585",
> +               .desc = "Freescale erratum a005858",
>                 .read_cntp_tval_el0 = fsl_a008585_read_cntp_tval_el0,
>                 .read_cntv_tval_el0 = fsl_a008585_read_cntv_tval_el0,
>                 .read_cntvct_el0 = fsl_a008585_read_cntvct_el0,
> @@ -190,13 +192,78 @@ static const struct arch_timer_erratum_workaround ool_workarounds[] = {
>  #endif
>  #ifdef CONFIG_HISILICON_ERRATUM_161010101
>         {
> +               .match_type = ate_match_dt,
>                 .id = "hisilicon,erratum-161010101",
> +               .desc = "HiSilicon erratum 161010101",
>                 .read_cntp_tval_el0 = hisi_161010101_read_cntp_tval_el0,
>                 .read_cntv_tval_el0 = hisi_161010101_read_cntv_tval_el0,
>                 .read_cntvct_el0 = hisi_161010101_read_cntvct_el0,
>         },
>  #endif
>  };
> +
> +typedef bool (*ate_match_fn_t)(const struct arch_timer_erratum_workaround *,
> +                              const void *);
> +
> +static
> +bool arch_timer_check_dt_erratum(const struct arch_timer_erratum_workaround *wa,
> +                                const void *arg)
> +{
> +       const struct device_node *np = arg;
> +
> +       return of_property_read_bool(np, wa->id);
> +}
> +
> +static const struct arch_timer_erratum_workaround *
> +arch_timer_iterate_errata(enum arch_timer_erratum_match_type type,
> +                         ate_match_fn_t match_fn,
> +                         void *arg)
> +{
> +       int i;
> +
> +       for (i = 0; i < ARRAY_SIZE(ool_workarounds); i++) {
> +               if (ool_workarounds[i].match_type != type)
> +                       continue;
> +
> +               if (match_fn(&ool_workarounds[i], arg))
> +                       return &ool_workarounds[i];
> +       }
> +
> +       return NULL;
> +}
> +
> +static
> +void arch_timer_enable_workaround(const struct arch_timer_erratum_workaround *wa)
> +{
> +       timer_unstable_counter_workaround = wa;
> +       static_branch_enable(&arch_timer_read_ool_enabled);
> +}
> +
> +static void arch_timer_check_ool_workaround(enum arch_timer_erratum_match_type type,
> +                                           void *arg)
> +{
> +       const struct arch_timer_erratum_workaround *wa;
> +       ate_match_fn_t match_fn = NULL;
> +
> +       if (static_branch_unlikely(&arch_timer_read_ool_enabled))
> +               return;
> +
> +       switch (type) {
> +       case ate_match_dt:
> +               match_fn = arch_timer_check_dt_erratum;
> +               break;

hey Marc,
   Would it make sense to have a default case here that warns &
returns? That wouldn't get hit by this series as-is, but might avoid a
NULL callback in the future.

  -dann

> +       }
> +
> +       wa = arch_timer_iterate_errata(type, match_fn, arg);
> +       if (!wa)
> +               return;
> +
> +       arch_timer_enable_workaround(wa);
> +       pr_info("Enabling global workaround for %s\n", wa->desc);
> +}
> +
> +#else
> +#define arch_timer_check_ool_workaround(t,a)           do { } while(0)
>  #endif /* CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND */
>
>  static __always_inline
> @@ -960,17 +1027,8 @@ static int __init arch_timer_of_init(struct device_node *np)
>
>         arch_timer_c3stop = !of_property_read_bool(np, "always-on");
>
> -#ifdef CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND
> -       for (i = 0; i < ARRAY_SIZE(ool_workarounds); i++) {
> -               if (of_property_read_bool(np, ool_workarounds[i].id)) {
> -                       timer_unstable_counter_workaround = &ool_workarounds[i];
> -                       static_branch_enable(&arch_timer_read_ool_enabled);
> -                       pr_info("arch_timer: Enabling workaround for %s\n",
> -                               timer_unstable_counter_workaround->id);
> -                       break;
> -               }
> -       }
> -#endif
> +       /* Check for globally applicable workarounds */
> +       arch_timer_check_ool_workaround(ate_match_dt, np);
>
>         /*
>          * If we cannot rely on firmware initializing the timer registers then
> --
> 2.11.0
>