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

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Message-ID: <1jttvi9vnq.fsf@starbuckisacylon.baylibre.com>
Date:   Thu, 08 Jun 2023 10:53:31 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Yu Tu <yu.tu@...ogic.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


>>> +
>>> +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

>> 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.

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