linux-kernel - Re: [PATCH V6 3/3] clk: meson: s4: add support for Amlogic S4 SoC peripheral clock controller

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Message-ID: <37e5d1a9-9379-a7ff-e288-9a4b80a0cc5f@amlogic.com>
Date:   Mon, 30 Jan 2023 17:59:34 +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 <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>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
CC:     "kelvin . zhang" <Kelvin.Zhang@...ogic.com>,
        "qi . duan" <qi.duan@...ogic.com>
Subject: Re: [PATCH V6 3/3] clk: meson: s4: add support for Amlogic S4 SoC
 peripheral clock controller



On 2023/1/30 17:47, Jerome Brunet wrote:
> [ EXTERNAL EMAIL ]
> 
> 
> On Mon 30 Jan 2023 at 17:41, Yu Tu <yu.tu@...ogic.com> wrote:
> 
>> On 2023/1/30 17:06, Jerome Brunet wrote:
>>> [ EXTERNAL EMAIL ]
>>> On Sat 28 Jan 2023 at 18:17, Yu Tu <yu.tu@...ogic.com> wrote:
>>>
>>>> On 2023/1/20 17:47, Jerome Brunet wrote:
>>>>> [ EXTERNAL EMAIL ]
>>>>> On Fri 20 Jan 2023 at 11:33, Yu Tu <yu.tu@...ogic.com> wrote:
>>>>>
>>>>>> Hi
>>>>>> On 2023/1/19 19:37, Jerome Brunet wrote:
>>>>>>> [ EXTERNAL EMAIL ]
>>>>>>> On Mon 16 Jan 2023 at 15:42, Yu Tu <yu.tu@...ogic.com> wrote:
>>>>>>>
>>>>>>>> Add the peripherals clock controller driver in the s4 SoC family.
>>>>>>>>
>>>>>>>> Signed-off-by: Yu Tu <yu.tu@...ogic.com>
>>>>>>> [...]
>>>>>>>
>>>>>>>> +
>>>>>>>> +/* Video Clocks */
>>>>>>>> +static struct clk_regmap s4_vid_pll_div = {
>>>>>>>> +	.data = &(struct meson_vid_pll_div_data){
>>>>>>>> +		.val = {
>>>>>>>> +			.reg_off = CLKCTRL_VID_PLL_CLK_DIV,
>>>>>>>> +			.shift   = 0,
>>>>>>>> +			.width   = 15,
>>>>>>>> +		},
>>>>>>>> +		.sel = {
>>>>>>>> +			.reg_off = CLKCTRL_VID_PLL_CLK_DIV,
>>>>>>>> +			.shift   = 16,
>>>>>>>> +			.width   = 2,
>>>>>>>> +		},
>>>>>>>> +	},
>>>>>>>> +	.hw.init = &(struct clk_init_data) {
>>>>>>>> +		.name = "vid_pll_div",
>>>>>>>> +		/*
>>>>>>>> +		 * The frequency division from the hdmi_pll clock to the vid_pll_div
>>>>>>>> +		 * clock is the default value of this register. When designing the
>>>>>>>> +		 * video module of the chip, a default value that can meet the
>>>>>>>> +		 * requirements of the video module will be solidified according
>>>>>>>> +		 * to the usage requirements of the chip, so as to facilitate chip
>>>>>>>> +		 * simulation. So this is ro_ops.
>>>>>>>> +		 * It is important to note that this clock is not used on this
>>>>>>>> +		 * chip and is described only for the integrity of the clock tree.
>>>>>>>> +		 */
>>>>>>> If it is reset value and will be applicable to all the design, regarless
>>>>>>> of the use-case, then yes RO ops is OK
>>>>>>>
>>>>>>> >From what I understand here, the value will depend on the use-case requirements.
>>>>>>> This is a typical case where the DT prop "assigned-rate" should be used, not RO ops.
>>>>>>
>>>>>> Check the previous chip history, the actual scene is not used at all,
>>>>>> basically is used in simulation. So the previous SOC was "ro_ops" without
>>>>>> any problems.  This S4 SOC is not actually useful either.
>>>>>>
>>>>>> So when you were upstream, you had no problem making "ro_ops". I wonder if
>>>>>> I could delete this useless clock, so you don't have to worry about it.
>>>>> I don't know what to make of this. What is the point of adding a useless
>>>>> clock ?
>>>>
>>>> As explained earlier this "vid_pll_div" is actually used in chip
>>>> emulation. So next I'd like to know what you suggest to do with the clock?
>>>>
>>> If it does not exist in the actual SoC, please remove it
>>>
>>
>> If I remove it, the "vid_pll_sel" clock will be missing a parent
>> (vid_pll_div). I will use the table method and give the above reasons. Do
>> you accept this method?
> 
> Either the clock exists or it does not.
> 
> If the HW actually exist, it is expected to be properly described.
> If it does not, it obviously cannot be an input to another clock.
> 
> Please sort this out and make the necessary changes.
> 

The CLKCTRL_VID_PLL_CLK_DIV register is actually described, but it is 
not used in the actual board. According to your reply just now, 
description is required, but I want to know how to describe it to meet 
your requirements.

Please give me some suggestions.