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Date: Mon, 4 Mar 2024 16:41:17 -0800
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Subject: Re: [PATCH v4 1/3] dt-bindings: hwmon: fan: Add fan binding to schema
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To: Zev Weiss <zev@bewilderbeest.net>, baneric926@gmail.com
Cc: jdelvare@suse.com, robh+dt@kernel.org, krzysztof.kozlowski+dt@linaro.org,
 conor+dt@kernel.org, corbet@lwn.net, linux-hwmon@vger.kernel.org,
 devicetree@vger.kernel.org, kcfeng0@nuvoton.com, kwliu@nuvoton.com,
 openbmc@lists.ozlabs.org, linux-doc@vger.kernel.org,
 linux-kernel@vger.kernel.org, DELPHINE_CHIU@wiwynn.com,
 naresh.solanki@9elements.com, billy_tsai@aspeedtech.com,
 Rob Herring <robh@kernel.org>
References: <20240227005606.1107203-1-kcfeng0@nuvoton.com>
 <20240227005606.1107203-2-kcfeng0@nuvoton.com>
 <1cf69d3e-a8b4-49f6-ac4d-550b525e45e2@hatter.bewilderbeest.net>
From: Guenter Roeck <linux@roeck-us.net>
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On 3/4/24 16:22, Zev Weiss wrote:
> On Mon, Feb 26, 2024 at 04:56:04PM PST, baneric926@gmail.com wrote:
>> From: Naresh Solanki <naresh.solanki@9elements.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
>>      $ref: fan-common.yaml#
>>      unevaluatedProperties: false
>>
>> Reviewed-by: Rob Herring <robh@kernel.org>
>> Signed-off-by: Naresh Solanki <naresh.solanki@9elements.com>
>> Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
>> Signed-off-by: Ban Feng <kcfeng0@nuvoton.com>
>> ---
>> .../devicetree/bindings/hwmon/fan-common.yaml | 78 +++++++++++++++++++
>> 1 file changed, 78 insertions(+)
>> create mode 100644 Documentation/devicetree/bindings/hwmon/fan-common.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/hwmon/fan-common.yaml b/Documentation/devicetree/bindings/hwmon/fan-common.yaml
>> new file mode 100644
>> index 000000000000..15c591c74545
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/hwmon/fan-common.yaml
>> @@ -0,0 +1,78 @@
>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
>> +%YAML 1.2
>> +---
>> +$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@9elements.com>
>> +  - Billy Tsai <billy_tsai@aspeedtech.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