linux-kernel - Re: [PATCH V5 3/4] clk: meson: s4: add s4 SoC peripheral clock controller driver and bindings

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Message-ID: <c9551542-6224-f443-bfce-cc537771220b@amlogic.com>
Date:   Mon, 28 Nov 2022 22:02:47 +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@...ogic.com>
Subject: Re: [PATCH V5 3/4] clk: meson: s4: add s4 SoC peripheral clock
 controller driver and bindings

Hi Jerome,

On 2022/11/28 20:23, Jerome Brunet wrote:
> [ EXTERNAL EMAIL ]
> 
> 
> On Mon 28 Nov 2022 at 16:08, Yu Tu <yu.tu@...ogic.com> wrote:
> 
>>>> +
>>>> +/*
>>>> + * This RTC clock can be supplied by an external 32KHz crystal oscillator.
>>>> + * If it is used, it should be documented in using fw_name and documented in the
>>>> + * Bindings. Not currently in use on this board, so skip it.
>>>> + */
>>>> +static u32 rtc_clk_sel[] = { 0, 1 };
>>> No reason to do that
>>
>> I'm going to change it to static u32 rtc_clk_sel[] = { 0, 1, 2 };.
>> I don't know if that's okay with you?
> 
> ... then there is no need to specify this table.
> 

I got it.I'll change it as you suggest.

> 
> 
>>
>>>
>>>> +static const struct clk_parent_data rtc_clk_sel_parent_data[] = {
>>>> +	{ .hw = &s4_rtc_32k_by_oscin.hw },
>>>> +	{ .hw = &s4_rtc_32k_by_oscin_div.hw },
>>>> +	{ .fw_name = "ext_32k",  }
>>>> +};
>>>> +
>>>> +static struct clk_regmap s4_rtc_clk = {
>>>> +	.data = &(struct clk_regmap_mux_data) {
>>>> +		.offset = CLKCTRL_RTC_CTRL,
>>>> +		.mask = 0x3,
>>>> +		.shift = 0,
>>>> +		.table = rtc_clk_sel,
>>>> +		.flags = CLK_MUX_ROUND_CLOSEST,
>>>> +	},
>>>> +	.hw.init = &(struct clk_init_data){
>>>> +		.name = "rtc_clk_sel",
>>>> +		.ops = &clk_regmap_mux_ops,
>>>> +		.parent_data = rtc_clk_sel_parent_data,
>>>> +		.num_parents = 2,
>>>> +		.flags = CLK_SET_RATE_PARENT,
>>>> +	},
>>>> +};
>>>> +
> 
> [...]
> 
>>>> +
>>>> +/* 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",
>>>> +		/* Same to g12a */
>>>> +		.ops = &meson_vid_pll_div_ro_ops,
>>> Please add an helpful explanation.
>>> 'Same to g12a' is not helpful.
>>>
>>
>> "Because the vid_pll_div clock is a clock that does not need to change the
>> divisor, ops only provides meson_vid_pll_div_ro_ops."
>> I wonder if this description is ok for you?
> 
> I understand this divider will not change with RO ops.
> I'm interrested why it does not change and how it is expected to be setup.
> 

Maybe you can be more specific, I don't understand, you're interested in 
that part of it specifically.

I don't know if you have the document of chip. If not, I can provide it 
to you privately. You can ask specific questions in conjunction with 
your documentation and submission(The original submission came from you.).
I can give you a specific answer or ask the chip designer to give you a 
reply.Do you think that's okay with you

>>
>>>> +		.parent_data = (const struct clk_parent_data []) {
>>>> +			{ .fw_name = "hdmi_pll", }
>>>> +		},
>>>> +		.num_parents = 1,
>>>> +		.flags = CLK_SET_RATE_PARENT,
>>>> +	},
>>>> +};
> 
> [...]
> 
>>>> +
>>>> +static struct clk_regmap s4_vclk_sel = {
>>>> +	.data = &(struct clk_regmap_mux_data){
>>>> +		.offset = CLKCTRL_VID_CLK_CTRL,
>>>> +		.mask = 0x7,
>>>> +		.shift = 16,
>>>> +	},
>>>> +	.hw.init = &(struct clk_init_data){
>>>> +		.name = "vclk_sel",
>>>> +		.ops = &clk_regmap_mux_ops,
>>>> +		.parent_data = s4_vclk_parent_data,
>>>> +		.num_parents = ARRAY_SIZE(s4_vclk_parent_data),
>>>> +	},
>>> You are stopping rate propagation here.
>>> It deserves an explanation. Same goes below.
>>
>> "When the driver uses this clock, needs to specify the patent clock he
>> wants in the dts."
>> Is ok for you?
> 
> Then you still don't understand the clock flag usage.
> 
> Preserving the parent selection (CLK_SET_RATE_NO_REPARENT) and rate
> propagation (CLK_SET_RATE_PARENT) is not the same thing.
> 
> As it stands, your comment is not aliged with what you do.
> 

Thanks for the explanation of flag.
My goal is to have the clock user describe themselves in DTS using the 
parent, or using the assigned-clocks and assigned-clock-parents settings 
in DTS. According to your explanation, some clocks like this should use 
CLK_SET_RATE_NO_REPARENT, right?

>>
>>>
>>>> +};
> 
> .