kern/58331: amdsmn(4) rescan doesn't notice duplicate children

[campbell+netbsd%mumble.net@localhost]

>Number:         58331
>Category:       kern
>Synopsis:       amdsmn(4) rescan doesn't notice duplicate children
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jun 10 02:45:00 +0000 2024
>Originator:     Taylor R Campbell
>Release:        current, 10, 9, ...
>Organization:
The NetAMDSMN Foundation
>Environment:
>Description:
amdsmn(4) scans for children such as amdzentemp(4).

But once the children are already attached, rescanning for children attaches _new_ instances of the same driver.

So if at boot you have

amdzentemp0 at amdsmn0,

then when you run `drvctl -r amdsmn0', you get a new

amdzentemp1 at amdsmn0

and if you do it again you get

amdzentemp2 at amdsmn0

and so on, with envstat(8) output growing increasingly large having more and more copies of the same sensors.
>How-To-Repeat:
drvctl -r amdsmn0
>Fix:
Yes, please!

We need some scheme to identify when a child _driver_ is already attached, and not attach another one.

It would also be nice if this had hooks for new drivers to be modloaded, too, e.g. for an AMD EDAC driver.  But maybe there's no convenient way to do that, so maybe the scheme of a few fixed interface attributes is the best we can do, like sys/dev/acpi/acpi.c.