Re: [PATCH 05/10] hwmon: generic-pwm-tachometer: Add generic PWM based tachometer

[Guenter Roeck]

On 03/07/2018 10:06 PM, Laxman Dewangan wrote:
> 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?

No. I hear you clearly that you for some reason dislike fan[1..n]_input.
While ABIs are not always to our liking, that doesn't mean that we get
to change them at our whim. If that is not acceptable for you, I can't
help you. And you can't change inX_input to inX_voltage either, sorry.

Guenter