Help needed. Default value for a event parameter (param=?)

I have a question about perf event parameter. I am trying to add an event parameter which should take a default value if not input by the user.

I have the event added in sys/bus/event_source/devices/<pmu>/events/ and there is a configurable event parameter "unit=?"
ex: event=0x301,units=?

The perf list list it as below

# perf list
<pmu>/<event_alias>,units=?/ [Kernel PMU event]

Now I have a requirement that If user does not pass any value for the parameter "unit" I should take a default value in my PMU implementation. Is this supported?

If not please guide me on where the change is needed. Any suggestions are appreciated.

Thanks,
Anurup