linux-kernel - Re: [PATCH v12 2/3] dt-bindings: hwmon: Support Aspeed g6 PWM TACH Control

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Message-ID: <c4550e34-17c8-4c67-9483-d654aa051d2d@linaro.org>
Date: Mon, 15 Jan 2024 10:26:41 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Billy Tsai <billy_tsai@...eedtech.com>, Rob Herring <robh@...nel.org>
Cc: "jdelvare@...e.com" <jdelvare@...e.com>,
 "linux@...ck-us.net" <linux@...ck-us.net>,
 "krzysztof.kozlowski+dt@...aro.org" <krzysztof.kozlowski+dt@...aro.org>,
 "joel@....id.au" <joel@....id.au>, "andrew@...id.au" <andrew@...id.au>,
 "corbet@....net" <corbet@....net>,
 "thierry.reding@...il.com" <thierry.reding@...il.com>,
 "u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.de>,
 "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
 "naresh.solanki@...ements.com" <naresh.solanki@...ements.com>,
 "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
 "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
 "linux-arm-kernel@...ts.infradead.org"
 <linux-arm-kernel@...ts.infradead.org>,
 "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
 "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
 BMC-SW <BMC-SW@...eedtech.com>, "patrick@...cx.xyz" <patrick@...cx.xyz>
Subject: Re: [PATCH v12 2/3] dt-bindings: hwmon: Support Aspeed g6 PWM TACH
 Control

On 15/01/2024 09:43, Billy Tsai wrote:
>>>>> +examples:
>>>>> +  - |
>>>>> +    #include <dt-bindings/clock/aspeed-clock.h>
>>>>> +    pwm_tach: pwm-tach-controller@...10000 {
>>>>> +      compatible = "aspeed,ast2600-pwm-tach";
>>>>> +      reg = <0x1e610000 0x100>;
>>>>> +      clocks = <&syscon ASPEED_CLK_AHB>;
>>>>> +      resets = <&syscon ASPEED_RESET_PWM>;
>>>>> +      #pwm-cells = <3>;
>>>>> +
>>>>> +      fan-0 {
>>>>> +        tach-ch = /bits/ 8 <0x0>;
>>>>> +      };
>>>>> +
>>>>> +      fan-1 {
>>>>> +        tach-ch = /bits/ 8 <0x1 0x2>;
>>>>> +      };
>>>
>>>> NAK on this based on how you are using pwm-fan in v10 discussion. See my
>>>> comments there.
>>>
>>> Okay, I will merge everything from the pwm-fan0 node into the fan-0 node
>>> and add the 'simple-bus' to the compatible string of the pwm_tach node.
> 
>> What simple-bus has anything to do with it? This is not a bus. Just to
>> remind: we talk about bindings, not driver.
> 
> Hi Krzysztof,
> 
> If I want to create a dt-binding to indicate that the child nodes
> should be treated as platform devices, which will be probed based on the

probed? Bindings do not probe. You ignored:
"we talk about bindings, not driver."

> compatible string, can I add "simple-bus" for our pwm_tach node like the
> following?

No, because this is not a bus.

> pwm_tach: pwm-tach-controller@...10000 {
>         compatible = "aspeed,ast2600-pwm-tach", "simple-bus";
>         reg = <0x1e610000 0x100>;
>         clocks = <&syscon ASPEED_CLK_AHB>;
>         resets = <&syscon ASPEED_RESET_PWM>;
>         #pwm-cells = <3>;
>   
>         fan-0 {
>           tach-ch = /bits/ 8 <0x0>;
>           compatible = "pwm-fan";
>           pwms = <&pwm_tach 0 40000 0>;
>         };
>   
>         fan-1 {
>           tach-ch = /bits/ 8 <0x1 0x2>;
>           compatible = "pwm-fan";
>           pwms = <&pwm_tach 1 40000 0>;
>         };
>       };
> Or do you have any other suggestions for describing this in the dt-bindings?


There is no need to describe it in the bindings. The existing compatible
describes it sufficiently. Your pwms now duplicate the tach-ch... I
don't understand what you want to achieve here in terms of hardware
description (again, please steer away from talking about Linux drivers
and probing, it's not related).

Best regards,
Krzysztof