linux-kernel - Re: [PATCH V3 3/6] clk: meson: S4: add support for Amlogic S4 SoC PLL clock driver

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Message-ID: <21e14cc1-6b34-e6b0-8da2-ad4b34dac149@amlogic.com>
Date:   Wed, 21 Sep 2022 16:40:34 +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 <narmstrong@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Subject: Re: [PATCH V3 3/6] clk: meson: S4: add support for Amlogic S4 SoC PLL
 clock driver

Hi Jerome，

On 2022/8/30 15:37, Yu Tu wrote:
> 
> 
> On 2022/8/30 14:44, Jerome Brunet wrote:
>> [ EXTERNAL EMAIL ]
>>
>>
>> On Tue 30 Aug 2022 at 14:13, Yu Tu <yu.tu@...ogic.com> wrote:
>>
>>> On 2022/8/29 17:48, Jerome Brunet wrote:
>>>> [ EXTERNAL EMAIL ]
>>>> On Mon 15 Aug 2022 at 21:20, Yu Tu <yu.tu@...ogic.com> wrote:
>>>>
>>>>>>>> +
>>>>>>>> +static struct clk_regmap s4_hdmi_pll_dco = {
>>>>>>>> +    .data = &(struct meson_clk_pll_data){
>>>>>>>> +        .en = {
>>>>>>>> +            .reg_off = ANACTRL_HDMIPLL_CTRL0,
>>>>>>>> +            .shift   = 28,
>>>>>>>> +            .width   = 1,
>>>>>>>> +        },
>>>>>>>> +        .m = {
>>>>>>>> +            .reg_off = ANACTRL_HDMIPLL_CTRL0,
>>>>>>>> +            .shift   = 0,
>>>>>>>> +            .width   = 8,
>>>>>>>> +        },
>>>>>>>> +        .n = {
>>>>>>>> +            .reg_off = ANACTRL_HDMIPLL_CTRL0,
>>>>>>>> +            .shift   = 10,
>>>>>>>> +            .width   = 5,
>>>>>>>> +        },
>>>>>>>> +        .frac = {
>>>>>>>> +            .reg_off = ANACTRL_HDMIPLL_CTRL1,
>>>>>>>> +            .shift   = 0,
>>>>>>>> +            .width   = 17,
>>>>>>>> +        },
>>>>>>>> +        .l = {
>>>>>>>> +            .reg_off = ANACTRL_HDMIPLL_CTRL0,
>>>>>>>> +            .shift   = 31,
>>>>>>>> +            .width   = 1,
>>>>>>>> +        },
>>>>>>>> +        .rst = {
>>>>>>>> +            .reg_off = ANACTRL_HDMIPLL_CTRL0,
>>>>>>>> +            .shift   = 29,
>>>>>>>> +            .width   = 1,
>>>>>>>> +        },
>>>>>>>> +    },
>>>>>>>> +    .hw.init = &(struct clk_init_data){
>>>>>>>> +        .name = "hdmi_pll_dco",
>>>>>>>> +        .ops = &meson_clk_pll_ro_ops,
>>>>>>>> +        .parent_data = (const struct clk_parent_data []) {
>>>>>>>> +            { .fw_name = "xtal", }
>>>>>>>> +        },
>>>>>>>> +        .num_parents = 1,
>>>>>>>> +        /*
>>>>>>>> +         * Display directly handle hdmi pll registers ATM, we need
>>>>>>>> +         * NOCACHE to keep our view of the clock as accurate as
>>>>>>>> +         * possible
>>>>>>>> +         */
>>>>>>>
>>>>>>> Is it really ?
>>>>>>>
>>>>>>> Given that HDMI support for the s4 is there yet, the
>>>>>>> addresses have changes and the region is no longer a syscon, it 
>>>>>>> is time
>>>>>>> for the HDMI driver to get fixed.
>>>>> The HDMI PLL is configured in the Uboot phase and does not change the
>>>>> frequency in the kernel phase. So we use the NOCACHE flag and
>>>>> "ro_ops".
>>>> That's no reason to put NOCACHE or ro-ops
>>>> If you want the frequencies to be statically assinged, the correct way
>>>> would be through assigned-rate in DT I guess.
>>>
>>> Okay. You're right. However, when registering with OPS, HDMI PLL will be
>>> reset. It takes time for PLL to stabilize the output frequency, which 
>>> will
>>> lead to the startup screen flashing.
>>>
>>> I would like to know how to solve this problem if not using ro_ops.
>>>
>>>>
>>
>> You can add new ops or tweak the current init function.
> 
> HDMI PLL is not different from other PLLS, so I think adding OPS is weird.
> 
>>
>> Safest would be to do the following :
>>   * Check if the PLLs is already on.
>>   * Check if the 'pll->init_regs' matches what is already set
>>     - if so, you can skip the reset
>>     - if not, you need to reset as usual
> 
> static int meson_clk_pll_init(struct clk_hw *hw)
> {
>          struct clk_regmap *clk = to_clk_regmap(hw);
>          struct meson_clk_pll_data *pll = meson_clk_pll_data(clk);
> 
> 
>          if (pll->init_count) {
>                  meson_parm_write(clk->map, &pll->rst, 1);
>                  regmap_multi_reg_write(clk->map, pll->init_regs,
>                                  |      pll->init_count);
>                  meson_parm_write(clk->map, &pll->rst, 0);
>          }
> 
> 
>          return 0;
> }
> 
> Because the init function looks like this. Therefore, HDMI PLL 
> init_count is not given. Can I change it like this?

I don't know if this change meets your requirements? Please give us your 
valuable advice.