linux-kernel - Re: [v6 2/4] dt-bindings: hwmon: Add ASPEED TACH Control documentation

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Message-ID: <f76f89a0-7773-6f64-c890-293093d4aba3@roeck-us.net>
Date:   Thu, 8 Jun 2023 06:18:10 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Billy Tsai <billy_tsai@...eedtech.com>,
        "jdelvare@...e.com" <jdelvare@...e.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "joel@....id.au" <joel@....id.au>,
        "andrew@...id.au" <andrew@...id.au>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.de>,
        "corbet@....net" <corbet@....net>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "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-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "patrick@...cx.xyz" <patrick@...cx.xyz>
Subject: Re: [v6 2/4] dt-bindings: hwmon: Add ASPEED TACH Control
 documentation

On 6/7/23 23:21, Billy Tsai wrote:
>          > The code says:
> 
>          > In Aspeed AST2600 SoC features 16 TACH controllers, with each
> 
>          > controller capable of supporting up to 1 input.
> 
>          > which is a bit different. I guess there are no examples anymore,
> 
>          > but I'd really like to see how this looks like in the devicetree file,
> 
>          > and how the driver is supposed to distinguish/select the 16 inputs.
> 
> Hi Roeck,
> 
> The node in the devicetree file will looks like following:
> 
> tach0: tach0@...10008 {
> 
>          compatible = "aspeed,ast2600-tach";
> 
>          reg = <0x1e610008 0x8>;
> 
>          #address-cells = <1>;
> 
>          #size-cells = <0>;
> 
>          pinctrl-names = "default";
> 
>          pinctrl-0 = <&pinctrl_tach0_default>;
> 
>          clocks = <&syscon ASPEED_CLK_AHB>;
> 
>          resets = <&syscon ASPEED_RESET_PWM>;
> 
>          status = "disabled";
> 
> };
> 

Neither reg nor pinctrl is mentioned in the bindings. Maybe that is not needed nowadays,
but I find it confusing.

Either case, it is highly unusual that there would be 16 instances of this device
instead of one. Why is this done ? It doesn't really make sense to me.

Guenter