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SubjectRe: [PATCH 3/3] dt-bindings: hwmon: max31790: Add pwmout-pin-as-tach-input property
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On 3/11/24 10:34, Rob Herring wrote:
> On Mon, Mar 11, 2024 at 06:13:47PM +0700, Chanh Nguyen wrote:
>> Add pwmout-pin-as-tach-input property.
>>
>> Signed-off-by: Chanh Nguyen <chanh@os.amperecomputing.com>
>> ---
>> Documentation/devicetree/bindings/hwmon/max31790.yaml | 11 +++++++++++
>> 1 file changed, 11 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/hwmon/max31790.yaml b/Documentation/devicetree/bindings/hwmon/max31790.yaml
>> index 5a93e6bdebda..447cac17053a 100644
>> --- a/Documentation/devicetree/bindings/hwmon/max31790.yaml
>> +++ b/Documentation/devicetree/bindings/hwmon/max31790.yaml
>> @@ -25,6 +25,16 @@ properties:
>> reg:
>> maxItems: 1
>>
>> + pwmout-pin-as-tach-input:
>> + description: |
>> + An array of six integers responds to six PWM channels for
>> + configuring the pwm to tach mode.
>> + When set to 0, the associated PWMOUT produces a PWM waveform for
>> + control of fan speed. When set to 1, PWMOUT becomes a TACH input
>> + $ref: /schemas/types.yaml#/definitions/uint8-array
>> + maxItems: 6
>> + minItems: 6
>
> Seems incomplete. For example, fan tachs have different number of
> pulses per revolution, don't you need to know that too?
>

Per Documentation/ABI/testing/sysfs-class-hwmon:

What: /sys/class/hwmon/hwmonX/fanY_pulses
Description:
Number of tachometer pulses per fan revolution.

Integer value, typically between 1 and 4.

RW

This value is a characteristic of the fan connected to the
device's input, so it has to be set in accordance with the fan
model.

Should only be created if the chip has a register to configure
the number of pulses. In the absence of such a register (and
thus attribute) the value assumed by all devices is 2 pulses
per fan revolution.

We only expect the property (and attribute) to exist if the controller
supports it.

Guenter


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