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

From: Laxman Dewangan
Date: Thu Mar 08 2018 - 01:06:43 EST




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?