On Thu, Sep 07, 2023 at 07:17:55AM +0000, Billy Tsai wrote:

On Wed, Aug 30, 2023 at 08:32:00PM +0800, Billy Tsai wrote:

quoted

quoted

From: Naresh Solanki <redacted>

Add common fan properties bindings to a schema.

Bindings for fan controllers can reference the common schema for the
fan

quoted

quoted

+properties:
+  max-rpm:
+    description:
+      Max RPM supported by fan.
+    $ref: /schemas/types.yaml#/definitions/uint32

quoted

Physics will limit this to something much less than 2^32. Add some 
constraints. 10000?

quoted

quoted

+
+  min-rpm:
+    description:
+      Min RPM supported by fan.
+    $ref: /schemas/types.yaml#/definitions/uint32

quoted

ditto

quoted

quoted

+
+  pulses-per-revolution:
+    description:
+      The number of pulse from fan sensor per revolution.
+    $ref: /schemas/types.yaml#/definitions/uint32

quoted

Needs constraints. I assume this is never more than 4 (or 2 even)?

Do you think we should add the contraint in the common binding?
In my option, the limit of the max/min rpm should be declared by
the binding if necessary, because the usage of each fan monitor is
based on the connection of the tach pin.

Yes, I think we should have default limits.

Unless we go as far as a schema for every specific fan model, then there 
is actually no way we can have specific limits unless the fan 
controllers have some limits.

The most I see in tree for pulses-per-revolution is 2. There's no value 
in more. So set the max to 4 and then if anyone needs more they can bump 
the value.

Or maybe there's some electrical/mechanical design reason fans are 1 or 
2 pulses and we'll never see anything else? This document[1] seems to 
indicate that is indeed the case. (First hit googling "fan tach signal 
pulses")

quoted

quoted

+  div:

quoted

Too generic of a name.

quoted

quoted

+    description:
+      Fan clock divisor

quoted

But what is a fan clock?

This is the divisor for the tachometer sampling clock, which determines the sensitivity of the tach pin.
So, if the name of the property changes to 'tach-div,' is it acceptable to you?

That sounds like a property of the controller, not the fan, so it 
belongs in the controller binding. Is this really a common thing?

 

quoted

quoted

+    $ref: /schemas/types.yaml#/definitions/uint32
+
+  target-rpm:
+    description:
+      Target RPM the fan should be configured during driver probe.

quoted

What driver? By the time the OS driver runs, a bunch of other boot 
software has already run on modern systems. So this value would likely 
be used much earlier. The point is that when exactly is outside the 
scope of DT. This is "what RPM do I use in case of no other information 
(e.g. temperature)".

So, the description should be changed to 'The default desired fan speed in RPM,'
and we shouldn't mention the timing of the property's operation in the DT, is that correct?

Correct.

quoted

quoted

+    $ref: /schemas/types.yaml#/definitions/uint32
+
+  mode:

quoted

Too generic.

quoted

quoted

+    description:
+      Select the operational mode of the fan.

quoted

What are modes? Spin and don't spin?

The mode is used to indicate the driving mode of the fan (DC, PWM and so on).
So, if the name of the property changes to 'fan-driving-mode,' is it acceptable to you?

I tend to think that should be implied from the parent node and/or other 
properties. PWM if "pwms" property is present. DC if the supply is 
variable. We could also use compatible strings in the fan nodes if 
there's a need.

That reminds me, both of these modes probably need a table of 
voltage/duty-cycle to RPMs. I imagine it's not always a linear response.  
Naresh also privately sent me (don't do that) an updated common binding 
which we discussed the need for this. I expect him to comment further 
with details.

quoted

quoted

+    $ref: /schemas/types.yaml#/definitions/uint32
+
+  pwms:
+    description:
+      PWM provider.

quoted

maxItems: 1

quoted

I don't think there are fans with more than 1 PWM input?

Ok, I will add the constraint for the pwm input.

quoted

quoted

+
+  tach-ch:
+    description:
+      The tach channel used for the fan.
+    $ref: /schemas/types.yaml#/definitions/uint32

quoted

The existing ASpeed version of this property allows more than 1 entry. I 
don't understand how a fan would have 2 tach signals, but if so, the 
generic property should allow for that.

Ok, I will modify it to the uint32-array

Perhaps uint8-array to align with existing versions of the property.

quoted

Perhaps 'reg' should be defined in here with some text saying 'reg' 
corresponds to the fan controller specific id which may be the PWM+TACH 
channel, PWM channel (deprecated), or TACH channel. I think there are 
examples of all 3 of these cases.

I don't think it's necessary for the 'reg' because the case you mentioned is
already covered by the property 'tach-ch' and the 'pwms'.

Yes, but when we have N child nodes of the same thing, we usually have 
"reg" and its value corresponds to how the parent identifies each child. 
We already have a mixture using PWM or tach channel. Yes, this can all 
just be in the fan controllers binding, but putting it here would just 
document the options.

Rob


[1] http://www.comairrotron.com/methods-monitoring-fan-performance

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel