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Subject: Re: [PATCH 05/10] hwmon: generic-pwm-tachometer: Add generic PWM
 based tachometer
To:     Guenter Roeck <linux@roeck-us.net>,
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From:   Laxman Dewangan <ldewangan@nvidia.com>
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Date:   Thu, 8 Mar 2018 11:36:24 +0530
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On Wednesday 07 March 2018 07:50 PM, Guenter Roeck wrote:
> On 03/07/2018 01:47 AM, Rajkumar Rampelli wrote:
>>
>>>
>>> While I am not opposed to ABI changes, the merits of those would 
>>> need to be
>>> discussed on the mailing list. But replacing "fan1_input" with "rpm" is
>>> not an acceptable ABI change, even if it may measure something that 
>>> turns
>>> but isn't a fan.
>>>
>>> If this _is_ in fact supposed to be used for something else but 
>>> fans, we
>>> would have to discuss what that might be, and if hwmon is the 
>>> appropriate
>>> subsystem to measure and report it. This does to some degree lead 
>>> back to
>>> my concern of having the "fan" part of this patch series in the pwm 
>>> core.
>>> I am still not sure if that makes sense.
>>>
>>> Thanks,
>>> Guenter
>> I am planning to add tachometer support in pwm-fan.c driver 
>> (drivers/hwmon/) instead of adding new generic-pwm-tachometer.c 
>> driver. Measuring RPM value will be done in pwm-fan driver itself 
>> using pwm capture feature and will add new sysfs attributes under 
>> this driver to report rpm value of fan.
>
> There is an existing attribute to report the RPM of fans. It is called 
> fan[1..n]_input.
>
> "replacing "fan1_input" with "rpm" is not an acceptable ABI change"
>
> Preemptive NACK.

The RPM is measured speed via PWM signal capture  which is output from fan.
So should we have the fan[1..n]_output_rpm?