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: <9f9cf980-c0c6-d5c3-ced8-8ab50e392470@amlogic.com>
Date:   Tue, 30 Aug 2022 15:37:26 +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



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?