linux-kernel - Re: [v2 1/3] dt-bindings: Add bindings for aspeed pwm-tach.

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Date:   Wed, 2 Nov 2022 13:19:24 -0500
From:   Rob Herring <robh@...nel.org>
To:     Billy Tsai <billy_tsai@...eedtech.com>
Cc:     "jdelvare@...e.com" <jdelvare@...e.com>,
        "linux@...ck-us.net" <linux@...ck-us.net>,
        "joel@....id.au" <joel@....id.au>,
        "andrew@...id.au" <andrew@...id.au>,
        "lee.jones@...aro.org" <lee.jones@...aro.org>,
        "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>,
        "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>,
        BMC-SW <BMC-SW@...eedtech.com>,
        "garnermic@...a.com" <garnermic@...a.com>
Subject: Re: [v2 1/3] dt-bindings: Add bindings for aspeed pwm-tach.

On Tue, Nov 1, 2022 at 10:21 PM Billy Tsai <billy_tsai@...eedtech.com> wrote:
>
> Hi Rob,
>
> On 2022/11/2, 2:40 AM, "Rob Herring" <robh@...nel.org> wrote:
>
>   >  On Tue, Nov 01, 2022 at 05:51:54PM +0800, Billy Tsai wrote:
>   >  > This patch adds device binding for aspeed pwm-tach device which is a
>   >  > multi-function device include pwm and tach function and pwm/tach device
>   >  > bindings which should be the child-node of pwm-tach device.
>   >  >
>   >  > Signed-off-by: Billy Tsai <billy_tsai@...eedtech.com>
>   >  > ---
>   >  >  .../bindings/hwmon/aspeed,ast2600-tach.yaml   | 48 ++++++++++++
>   >  >  .../bindings/mfd/aspeed,ast2600-pwm-tach.yaml | 76 +++++++++++++++++++
>   >  >  .../bindings/pwm/aspeed,ast2600-pwm.yaml      | 64 ++++++++++++++++
>   >  >  3 files changed, 188 insertions(+)
>   >  >  create mode 100644 Documentation/devicetree/bindings/hwmon/aspeed,ast2600-tach.yaml
>   >  >  create mode 100644 Documentation/devicetree/bindings/mfd/aspeed,ast2600-pwm-tach.yaml
>   >  >  create mode 100644 Documentation/devicetree/bindings/pwm/aspeed,ast2600-pwm.yaml
>
>   >  I'm pretty sure I've said this before, but I'm not taking more fan
>   >  controller bindings without comming up with a common binding. Please see
>   >  this series[1] and help ensure it meets your needs.
>
>   >  Rob
>
>   >  [1] 20221013094838.1529153-2-Naresh.Solanki@...ements.com <https://lore.kernel.org/all/<a href=>/">https://lore.kernel.org/all/20221013094838.1529153-2-Naresh.Solanki@9elements.com/
>
> The link you provide doesn't meet my needs. This is fan binding.

A PWM and Tach controller is for fans, no?

As I said, contribute to it so that it does meet your needs.

> As I told before
> "This patch doesn't use to binding the fan control h/w. It is used to binding the two independent h/w blocks.
> One is used to provide pwm output and another is used to monitor the speed of the input."
> My patch is used to point out that the pwm and the tach is the different function and don't need to
> bind together. You can not only combine them as the fan usage but also treat them as the individual module for
> use. For example: the pwm can use to be the beeper (pwm-beeper.c), the tach can be used to monitor any device's speed.

That all sounds like requirements that you have which you should
ensure the fan binding can support.

I've already said to use the PWM binding in the fan binding exactly
for the purpose of hooking up the PWMs to other things. Whether the
tach controller is useful for something other than fans, I don't know.
Seems less likely. The max6639 also has a tach controller. So if other
uses are possible for you, then it could be possible for any other h/w
like the max6639.

Rob