linux-kernel - Re: [PATCH v4 1/3] dt-bindings: hwmon: fan: Add fan binding to schema

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Date: Mon, 4 Mar 2024 16:49:27 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Zev Weiss <zev@...ilderbeest.net>, baneric926@...il.com
Cc: jdelvare@...e.com, robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
 conor+dt@...nel.org, corbet@....net, linux-hwmon@...r.kernel.org,
 devicetree@...r.kernel.org, kcfeng0@...oton.com, kwliu@...oton.com,
 openbmc@...ts.ozlabs.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, DELPHINE_CHIU@...ynn.com,
 naresh.solanki@...ements.com, billy_tsai@...eedtech.com,
 Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v4 1/3] dt-bindings: hwmon: fan: Add fan binding to schema

On 3/4/24 16:41, Guenter Roeck wrote:

>>> +
>>> +  min-rpm:
>>> +    description:
>>> +      Min RPM supported by fan.
>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>> +    maximum: 1000
>>
>> I can't say with certainty that it's not, but are we sure 1000 is low enough?  Looking at just what I've got on hand, an 80mm fan I have will run steadily at about 1500RPM, and I'd assume larger ones (e.g. 120mm) could potentially go significantly lower...
>>
> 
> I have seen fans which run stable at < 400rpm.
> One of my systems right now has:
> 
> fan1:              732 RPM  (min =    0 RPM)
> fan2:                0 RPM  (min =    0 RPM)
> fan3:              586 RPM  (min =    0 RPM)
> fan4:              472 RPM  (min =    0 RPM)
> fan5:              480 RPM  (min =    0 RPM)
> 
> Those are 80mm fans. A quick check shows that various Noctua fans have a
> minimum speed of 300 rpm. So 1000 is indeed a bit high for the minimum speed.
> 

No, wait, that is the _maximum_ minimum speed. Got me there.

So, there is Noctua's NF-A4x20 PWM with a minimum rotational speed of 1,200 RPM.

If I interpret
https://www.mouser.com/datasheet/2/471/SanyoDenki_San_Ace_40LG28_E-3198440.pdf
correctly, it lists some fans with a minimum speed of 7,500 RPM.

Guenter