> ... bcs I run it on development machine so there are not so many other
> drivers enabled ;-)

You are not the only person who uses NetBSD, are you?

> But this brings me to an other question. How It is with driver's
> optimizations in NetBSD. Are there any restrictions or suggestions when
> using optimizations? Or can I use any level (-O0..3) as I wish?

Sometimes it might be caused by optimization bug, but sometimes
potential problem in wrong source is disclosed by optimization.
I.e. if there is some unintialized variable, compiler would try
reorder references of it. (BTW it isn't NetBSD problem but gcc)

Anyway, you could investigate which optimization causes your problem.
(I guess -fstrict-aliasing, -fgcse, or -fschedule-insns etc.)
---
Izumi Tsutsui