On 25/04/2024 16:05, Guenter Roeck wrote: > On 4/25/24 03:33, Chanh Nguyen wrote: >> >> >> On 24/04/2024 00:02, Conor Dooley wrote: >>> [EXTERNAL EMAIL NOTICE: This email originated from an external sender. Please be mindful of safe email handling and proprietary information protection practices.] >>> >> > > The quote doesn't make much sense. > >> Sorry Conor, there may be confusion here. I mean the mapping of the PWM output to the TACH input, which is on the MAX31790, and it is not sure a common feature on all fan controllers. >> > > I think the term "mapping" is a bit confusing here. > > tach-ch, as I understand it, is supposed to associate a tachometer input > with a pwm output, meaning the fan speed measured with the tachometer input > is expected to change if the pwm output changes. > > On MAX31790, it is possible to configure a pwm output pin as tachometer input pin. > That is something completely different. Also, the association is fixed. > If the first pwm channel is used as tachometer channel, it would show up as 7th > tachometer channel. If the 6th pwm channel is configured to be used as tachometer > input, it would show up as 12th tachometer channel. > > Overall, the total number of channels on MAX31790 is always 12. 6 of them > are always tachometer inputs, the others can be configured to either be a > pwm output or a tachometer input. > > pwm outputs on MAX31790 are always tied to the matching tachometer inputs > (pwm1 <--> tach1 etc) and can not be reconfigured, meaning tach-ch for > channel X would always be X. > >> I would like to open a discussion about whether we should use the tach-ch property on the fan-common.yaml >> >> I'm looking forward to hearing comments from everyone. For me, both tach-ch and vendor property are good. >> > > I am not even sure how to define tach-ch to mean "use the pwm output pin > associated with this tachometer input channel not as pwm output > but as tachometer input". That would be a boolean, not a number. Thanks for explanation. So this is basically pin controller function choice - kind of output or input, although not in terms of GPIO. Shouldn't we have then fan children which will be consumers of PWMs? Having a consumer makes pin PWM output. Then tach-ch says which pins are tachometer for given fan? Just like aspeed,g6-pwm-tach.yaml has? Best regards, Krzysztof
