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: <0c7e6d90-2ce3-25ab-84b6-026ce8a238a8@amlogic.com>
Date:   Tue, 30 Aug 2022 14:13:35 +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 2022/8/29 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.

>