linux-kernel - Re: [PATCH v4 8/9] mips: ralink: get cpu rate from new driver code

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Date:   Sat, 17 Jun 2023 21:01:09 +0200
From:   Sergio Paracuellos <sergio.paracuellos@...il.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     linux-clk@...r.kernel.org, linux-mips@...r.kernel.org,
        tsbogend@...ha.franken.de, john@...ozen.org,
        linux-kernel@...r.kernel.org, p.zabel@...gutronix.de,
        mturquette@...libre.com, sboyd@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, matthias.bgg@...il.com,
        devicetree@...r.kernel.org, arinc.unal@...nc9.com
Subject: Re: [PATCH v4 8/9] mips: ralink: get cpu rate from new driver code

On Sat, Jun 17, 2023 at 7:27 PM Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> wrote:
>
> On 17/06/2023 17:35, Sergio Paracuellos wrote:
> > On Sat, Jun 17, 2023 at 4:48 PM Krzysztof Kozlowski
> > <krzysztof.kozlowski@...aro.org> wrote:
> >>
> >> On 17/06/2023 07:24, Sergio Paracuellos wrote:
> >>> At very early stage on boot, there is a need to set 'mips_hpt_frequency'.
> >>> This timer frequency is a half of the CPU frequency. To get clocks properly
> >>> set we need to call to 'of_clk_init()' and properly get cpu clock frequency
> >>> afterwards. Depending on the SoC, CPU clock index in the clock provider is
> >>> different being two for MT7620 SoC and one for the rest. Hence, adapt code
> >>> to be aligned with new clock driver.
> >>
> >>
> >>>  void __init plat_time_init(void)
> >>>  {
> >>> +     struct of_phandle_args clkspec;
> >>>       struct clk *clk;
> >>> +     int cpu_clk_idx;
> >>>
> >>>       ralink_of_remap();
> >>>
> >>> -     ralink_clk_init();
> >>> -     clk = clk_get_sys("cpu", NULL);
> >>> +     cpu_clk_idx = clk_cpu_index();
> >>> +     if (cpu_clk_idx == -1)
> >>> +             panic("unable to get CPU clock index");
> >>> +
> >>> +     of_clk_init(NULL);
> >>> +     clkspec.np = of_find_node_by_name(NULL, "sysc");
> >>> +     clkspec.args_count = 1;
> >>> +     clkspec.args[0] = cpu_clk_idx;
> >>> +     clk = of_clk_get_from_provider(&clkspec);
> >>
> >> This is very obfuscated way of getting clock. Why can't you get it from
> >> "clocks" property of "cpu", like every other recent platform?
> >
> > I did not find any other approach that works for me. So I ended up in this one.
> > Can you point me out in a sample of code doing the same so I can check
> > if it works for me then?
>
> You mean bindings?
> git grep cpus.yaml
>
> Driver?
> git grep clk_get_rate
> clk_get
> eventually of_clk_get
>
> It all depends on the context.
>
> Anyway, it is very easy to find existing solutions not using
> of_find_node_by_name for your platform:
>
> git grep mips_hpt_frequency
>
> First result.

I have tested before all of these and got into panic because clock
cannot get retrieved:

For example first result is to make use of clk_get so change the code into:

void __init plat_time_init(void)
{
    struct clk *clk;

    of_clk_init(NULL);
    clk = clk_get(NULL, "cpu");
    if (IS_ERR(clk))
       panic("unable to get CPU clock, err=%ld", PTR_ERR(clk));

    pr_info("CPU Clock: %ldMHz\n", clk_get_rate(clk) / 1000000);
    mips_hpt_frequency = clk_get_rate(clk) / 2;
    clk_put(clk);
    timer_probe();
}

And I panic because I cannot get the cpu clock...

>
>
> Best regards,
> Krzysztof
>

Thanks,
    Sergio Paracuellos