linux-kernel - Re: [v6 1/4] dt-bindings: pwm: Add ASPEED PWM Control documentation

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Message-ID: <05038be8-f59d-5b2b-9b51-36094941f731@linaro.org>
Date:   Thu, 8 Jun 2023 11:26:02 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Billy Tsai <billy_tsai@...eedtech.com>,
        "jdelvare@...e.com" <jdelvare@...e.com>,
        "linux@...ck-us.net" <linux@...ck-us.net>,
        "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 1/4] dt-bindings: pwm: Add ASPEED PWM Control documentation

On 08/06/2023 10:57, Billy Tsai wrote:
> On 08/06/2023 10:21, Billy Tsai wrote:
>         >>         On 08/06/2023 09:47, Billy Tsai wrote:
>         >>         >>
>         >>         >>   >> +
>         >>         >>   >> +allOf:
>         >>         >>   >> +  - $ref: pwm.yaml#
>         >>         >>   >> +
>         >>         >>   >> +properties:
>         >>         >>   >> +  compatible:
>         >>         >>   >> +    enum:
>         >>         >>   >> +      - aspeed,ast2600-pwm
>         >>         >>   >> +
>         >>         >>   >> +  "#pwm-cells":
>         >>         >>   >> +    const: 3
>         >>         >>
>         >>         >>   > 3 cells? For one PWM? What are they?
>         >>         >>
>         >>         >> channel, period and polarity.
>         >>
>         >>         > Don't cut my responses. You wrote you have one PWM output, so only one
>         >>         > channel. What do you put then in the channel?
>         >>
>         >> You need to put 0 in the cell of the channel, the example of the dts usage will like following:
> 
>         > If you always put 0 isn't this a proof that it's wrong?
> 
> No, if your PWM controller only has one pwm output, then it should only be configured as 0.
> This is the usage of the pwm-cells property.
> https://github.com/torvalds/linux/blob/master/drivers/pwm/core.c#L129-L158

This is only when you use generic of_xlate. You do not have to use
generic of_xlate if it does not suite you. Again you speak about the
drivers, but we talk about bindings:

https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/pwm/pwm.txt#L13

"controller specific"

> https://github.com/torvalds/linux/blob/master/include/linux/pwm.h#LL299C20-L299C20
> All of the pwm driver with npwm = 1 will has the same usage.

So it seems many simplified their drivers...

Best regards,
Krzysztof