[PATCH v3 13/15] firmware: arm_scmi: Use bound iterators to minimize discovered rates

[Geert Uytterhoeven]

Hi Cristian,

On Tue, 28 Apr 2026 at 22:17, Cristian Marussi <cristian.marussi at arm.com> wrote:
> Clock rates are guaranteed to be returned in ascending order for SCMI clock
> protocol versions greater than 1.0: in such a case, use bounded iterators
> to minimize the number of message exchanges needed to discover min and max
> rate.
>
> Signed-off-by: Cristian Marussi <cristian.marussi at arm.com>

Thanks for your patch!

> +static int
> +scmi_clock_describe_rates_get(const struct scmi_protocol_handle *ph,
> +                             u32 clk_id, struct clock_info *cinfo)
> +{
> +       struct scmi_clock_desc *clkd = &cinfo->clkds[clk_id];
> +       int ret;
> +
> +       /*
> +        * Since only after SCMI Clock v1.0 the returned rates are guaranteed to
> +        * be discovered in ascending order, lazy enumeration cannot be use for
> +        * SCMI Clock v1.0 protocol.
> +        */
> +       if (PROTOCOL_REV_MAJOR(ph->version) > 0x1)
> +               ret = scmi_clock_describe_rates_get_lazy(ph, clkd);
> +       else
> +               ret = scmi_clock_describe_rates_get_full(ph, clkd);
> +
> +       if (ret)
> +               return ret;
> +
> +       clkd->info.min_rate = clkd->rates[RATE_MIN];
>         if (!clkd->rate_discrete) {
>                 clkd->info.max_rate = clkd->rates[RATE_MAX];
>                 dev_dbg(ph->dev, "Min %llu Max %llu Step %llu Hz\n",
>                         clkd->rates[RATE_MIN], clkd->rates[RATE_MAX],
>                         clkd->rates[RATE_STEP]);
>         } else {
> -               sort(clkd->rates, clkd->num_rates,
> -                    sizeof(clkd->rates[0]), rate_cmp_func, NULL);
>                 clkd->info.max_rate = clkd->rates[clkd->num_rates - 1];
> +               dev_dbg(ph->dev, "Clock:%s DISCRETE:%d -> Min %llu Max %llu\n",
> +                       clkd->info.name, clkd->rate_discrete,
> +                       clkd->info.min_rate, clkd->info.max_rate);

Printing clkd->rate_discrete is futile, as it is always 1.
It would be more useful to print clkd->r.num_rates instead, although
that may still be lower than the actual value, due to lazy handling.

>         }
> -       clkd->info.min_rate = clkd->rates[RATE_MIN];
>
>         return 0;
>  }

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds