linux-kernel - Re: [PATCH 5/5] riscv: dts: add clock generator for Sophgo SG2042 SoC

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Message-ID: <68220eb6-8a20-42d4-83e5-d0d45b2f1404@sifive.com>
Date:   Tue, 14 Nov 2023 21:15:17 -0500
From:   Samuel Holland <samuel.holland@...ive.com>
To:     Chen Wang <unicorn_wang@...look.com>,
        Conor Dooley <conor@...nel.org>,
        Chen Wang <unicornxw@...il.com>
Cc:     aou@...s.berkeley.edu, chao.wei@...hgo.com,
        krzysztof.kozlowski+dt@...aro.org, mturquette@...libre.com,
        palmer@...belt.com, paul.walmsley@...ive.com,
        richardcochran@...il.com, robh+dt@...nel.org, sboyd@...nel.org,
        devicetree@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        haijiao.liu@...hgo.com, xiaoguang.xing@...hgo.com
Subject: Re: [PATCH 5/5] riscv: dts: add clock generator for Sophgo SG2042 SoC

On 2023-11-14 7:34 PM, Chen Wang wrote:
> On 2023/11/15 1:31, Conor Dooley wrote:
>> On Mon, Nov 13, 2023 at 09:20:11PM +0800, Chen Wang wrote:
>>> From: Chen Wang <unicorn_wang@...look.com>
>>>
>>> Add clock generator node to device tree for SG2042, and enable clock for
>>> uart0.
>>>
>>> Signed-off-by: Chen Wang <unicorn_wang@...look.com>
>>> ---
>>>   arch/riscv/boot/dts/sophgo/sg2042-clock.dtsi | 76 ++++++++++++++++++++
>> There's no need to create an entirely new file for this.
> Agree, I will merge this into sg2042.dtsi in next revision.
>>
>>>   arch/riscv/boot/dts/sophgo/sg2042.dtsi       | 10 +++
>>>   2 files changed, 86 insertions(+)
>>>   create mode 100644 arch/riscv/boot/dts/sophgo/sg2042-clock.dtsi
>>>
>>> diff --git a/arch/riscv/boot/dts/sophgo/sg2042-clock.dtsi
>>> b/arch/riscv/boot/dts/sophgo/sg2042-clock.dtsi
>>> new file mode 100644
>>> index 000000000000..66d2723fab35
>>> --- /dev/null
>>> +++ b/arch/riscv/boot/dts/sophgo/sg2042-clock.dtsi
>>> @@ -0,0 +1,76 @@
>>> +// SPDX-License-Identifier: (GPL-2.0 OR MIT)
>>> +/*
>>> + * Copyright (C) 2023 Sophgo Technology Inc. All rights reserved.
>>> + */
>>> +
>>> +/ {
>>> +    cgi: oscillator {
>>> +        compatible = "fixed-clock";
>>> +        clock-frequency = <25000000>;
>>> +        clock-output-names = "cgi";
>>> +        #clock-cells = <0>;
>>> +    };
>> What actually is this oscillator?
>> Is it provided by another clock controller on the SoC, or is it provided
>> by an oscillator on the board?
> 
> This oscillator is an individual ic chip outside the SoC on the board, that's
> why I list it outside soc node.
> 
> Actually the "cgi" is abbrevation for "Clock Generation IC chip".

Since the oscillator is outside the SoC, this node (or at least its
clock-frequency property) belongs in the board devicetree, not the SoC .dtsi.
See [1].

Regards,
Samuel

[1]:
https://lore.kernel.org/linux-riscv/b5401052-e803-9788-64d6-82b2737533ce@linaro.org/