On 25/04/2024 21:05, Guenter Roeck wrote:
On 4/25/24 03:33, Chanh Nguyen wrote:
On 24/04/2024 00:02, Conor Dooley wrote:
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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.
Thank you, Guenter, for your explanation. That is also my understanding
of the MAX31790 feature.
So, I think we should introduce a vendor property to configure the pwm
output pins to become tachometer input pins. We shouldn't use the
tach-ch property. Because they are completely different, I think.
What's your idea ? Please help share me, Guenter
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.
Thank Guenter,
I reviewed again the "tach-ch" property, which is used in the
https://elixir.bootlin.com/linux/v6.9-rc6/source/Documentation/devicetree/bindings/hwmon/aspeed,g6-pwm-tach.yaml#L68
and
https://elixir.bootlin.com/linux/v6.9-rc6/source/drivers/hwmon/aspeed-g6-pwm-tach.c#L434
That is something completely different from my purpose.
Guenter
