linux-kernel - Re: [v5 3/5] dt-bindings: mfd: Add aspeed pwm-tach binding

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Message-ID: <c8fe71a4-f8bb-d0a5-a227-14040fa024a9@linaro.org>
Date:   Wed, 7 Jun 2023 10:55:08 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Billy Tsai <billy_tsai@...eedtech.com>,
        Patrick Williams <patrick@...cx.xyz>
Cc:     "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>,
        "lee@...nel.org" <lee@...nel.org>,
        "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>
Subject: Re: [v5 3/5] dt-bindings: mfd: Add aspeed pwm-tach binding

On 07/06/2023 08:26, Billy Tsai wrote:
>         >>
>         >> He felt what he was trying to accomplish met the documented
>         >> expectations.  Are there some changes that need to be done in mfd.txt to
>         >> further clarify when to use it and when not to?
> 
>         > I think mfd.txt clearly states:
>         > "For more complex devices, when the nexus driver has to
>         > probe registers to figure out what child devices exist etc, this should
>         > not be used. In the latter case the child devices will be determined by
>         > the operating system."
> 
> About the mfd:
> For our pwm and tach devices, there is no need to check/apply any hardware register from parent to determine child’s existence or functional.
> They don’t have any dependency on the parent node. In fact, it doesn’t require a specific driver to bind with the "aspeed,ast2600-pwm-tach" label. Their purpose is solely to share the same clock, reset phandle and base address. The main reason for using simple-mfd in this case is because these two independent devices share the same base address.

Actually one more thoughts. I have doubt that you have two independent
devices. If you share the clock, reset line and register address space,
this means *you do not have two independent devices*.

You have most likely only one device.

Best regards,
Krzysztof