linux-kernel - Re: [PATCH V9 3/4] clk: meson: S4: add support for Amlogic S4 SoC PLL clock driver

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Date:   Thu, 8 Jun 2023 17:30:52 +0800
From:   Yu Tu <yu.tu@...ogic.com>
To:     Jerome Brunet <jbrunet@...libre.com>, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Kevin Hilman <khilman@...libre.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     kelvin.zhang@...ogic.com, qi.duan@...ogic.com
Subject: Re: [PATCH V9 3/4] clk: meson: S4: add support for Amlogic S4 SoC PLL
 clock driver



On 2023/6/8 16:53, Jerome Brunet wrote:
> [ EXTERNAL EMAIL ]
> 
>>>> +
>>>> +static struct clk_regmap s4_fclk_div4 = {
>>>> +     .data = &(struct clk_regmap_gate_data){
>>>> +             .offset = ANACTRL_FIXPLL_CTRL1,
>>>> +             .bit_idx = 21,
>>>> +     },
>>>> +     .hw.init = &(struct clk_init_data){
>>>> +             .name = "fclk_div4",
>>>> +             /*
>>>> +              * For more information, please refer to s4_fixed_pll_dco.
>>>> +              */
>>> While div2 and div3 got an explanation from previous SoCs, they others -
>>> like div4/div7/etc ... - have been able to cope with rw ops so far.
>>> Why is the S4 different for all these clocks ?
>>
>> The chip was changed fixed pll for security reasons.
>>
>> Fixed PLL registers are not writable in the kernel phase. Write of fixed
>> PLL-related register will cause the system to crash.
>>
> 
> That is definitely worth mentionning

Can I understand that you agree with the use of "ro_ops" for FIXed PLL 
related clocks later?

> 
>>> Requiring RO ops (or fishy clock flags) is usually a sign that a clock
>>> is used without an appropriate driver.
>>>
> 
> Neil is currently dealing with the dt-bindings, please
> * Adjust your patchset accordingly
> * Wait for his v2 to land, you'll need it.

OKay.

> 
>>>> +             .ops = &clk_regmap_gate_ro_ops,
>>>> +             .parent_hws = (const struct clk_hw *[]) {
>>>> +                     &s4_fclk_div4_div.hw
>>>> +             },
>>>> +             .num_parents = 1,
>>>> +     },
>>>> +};
>>>> +