Hello.
I finally solved the problem.
I just detach and re-attach the wifi card physically and it worked.
First, I updated BIOS and nothing changed.
Then I made several changes to BIOS configuration.
I found that I've installed for legacy BIOS and MBR.
So I reinstalled OpenBSD for UEFI and GPT.
But the problem was not solved.
And at this morning, I recalled that I could use this wifi from Linux.
So I tried to boot from Linux live USB(Debian), and encountered a
similar problem of iwlwifi with error code -110.
I googled for this problem and found an article:
https://bugzilla.kernel.org/show_bug.cgi?id=205299
It implies that the problem has something to do with Windows.
Actually I installed Windows on this machine and my sister used it
until I installed OpenBSD last week.
I wondered if I could reset some configuration on the wifi card
made by Windows by disconnecting it from the motherboard.
And this worked for me.
Anyway, thanks a lot everyone.
Matsuda Kenji
