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 16:41:17 -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 16:22, Zev Weiss wrote:
> On Mon, Feb 26, 2024 at 04:56:04PM PST, baneric926@...il.com wrote:
>> From: Naresh Solanki <naresh.solanki@...ements.com>
>>
>> Add common fan properties bindings to a schema.
>>
>> Bindings for fan controllers can reference the common schema for the
>> fan
>>
>> child nodes:
>>
>>  patternProperties:
>>    "^fan@[0-2]":
>>      type: object
>>      $ref: fan-common.yaml#
>>      unevaluatedProperties: false
>>
>> Reviewed-by: Rob Herring <robh@...nel.org>
>> Signed-off-by: Naresh Solanki <naresh.solanki@...ements.com>
>> Signed-off-by: Billy Tsai <billy_tsai@...eedtech.com>
>> Signed-off-by: Ban Feng <kcfeng0@...oton.com>
>> ---
>> .../devicetree/bindings/hwmon/fan-common.yaml | 78 +++++++++++++++++++
>> 1 file changed, 78 insertions(+)
>> create mode 100644 Documentation/devicetree/bindings/hwmon/fan-common.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/hwmon/fan-common.yaml b/Documentation/devicetree/bindings/hwmon/fan-common.yaml
>> new file mode 100644
>> index 000000000000..15c591c74545
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/hwmon/fan-common.yaml
>> @@ -0,0 +1,78 @@
>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/hwmon/fan-common.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Common Fan Properties
>> +
>> +maintainers:
>> +  - Naresh Solanki <naresh.solanki@...ements.com>
>> +  - Billy Tsai <billy_tsai@...eedtech.com>
>> +
>> +properties:
>> +  max-rpm:
>> +    description:
>> +      Max RPM supported by fan.
>> +    $ref: /schemas/types.yaml#/definitions/uint32
>> +    maximum: 100000
>> +
>> +  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.

Guenter