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 19:27:05 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Sergio Paracuellos <sergio.paracuellos@...il.com>
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 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.


Best regards,
Krzysztof