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

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Date:   Mon, 30 Jan 2023 10:06:49 +0100
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>,
        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 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