Re: [PATCH v2 3/4] dt-bindings: watchdog: da9062: add watchdog timeout mode

On 30. 11. 21 18:46, Adam Thomson wrote:

On 30 November 2021 16:40, Guenter Roeck wrote:

quoted

quoted

quoted

Why does it need a value ? Why not just bool ?

One argument might be that if the property isn't provided then the OTP
configured value can persist without needing a FW change around this DT

binding.

quoted

My belief though is that the majority of users would have this property set to 0
by default in OTP, so a boolean would be OK I think here to enable watchdog
shutdown.

Sorry, you lost me.
	dlg,wdt-sd = <0>;
is the current situation, and identical to not having the property in
the first place.
	dlg,wdt-sd = <1>;
is new. I don't see the difference to
	dlg,wdt-sd;
vs. not having the property at all (which is, again, the current situation).
Since it has to be backward compatible,
	dlg,wdt-sd = <0>;
will always be identical to not having the property at all.
I can not find a situation where an integer would have any benefits over a
boolean.

So if you have a binary DT binding, it's either there or it isn't which implies
the bit to be set to 0/1 in this case. If you have a binding which has a value,
there can be 3 outcomes in this discussion:

  1) Binding = 0, bit is set to 0
  2) Binding = 1, bit is set to 1
  3) Binding NOT present in DT, OTP default value in HW remains untouched

Say a platform updates to a later kernel version, but sticks with existing DT
FW (i.e. the new boolean binding isn't present in FW), then the following could
happen:

  1) OTP for DA9061/2 has this bit set to 1, system expectation is that watchdog
     triggers SHUTDOWN.
  2) New driver checks existance of 'dlg,wdt-sd' but it's obviously not there so
     assumes the bit should be set to 0 and does so
  3) When the watchdog fires, it will no longer trigger SHUTDOWN but instead
     POWER-DOWN due to binary handling of new boolean binding.

This was my thinking exactly. I also first thought about boolean value, 
but I then moved to the integer value of 0 or 1 after checking the OTP 
default for this bit. The da9062 I'm working with has the bit set to 1 
by default.

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