802.11ac support for the iwm(4) driver

Stefan Sperling (stsp@) has added support for 802.11ac for the iwm(4) driver

This is great news! My laptop has an Intel Dual Band Wireless-AC 8265 that uses the iwm(4) driver.

I updated my snapshot and checked the output (sensitive bits redacted):

# ifconfig iwm0
        lladdr 00:21:6b:xx:xx:xx
        index 2 priority 4 llprio 3
        groups: wlan egress
        media: IEEE802.11 autoselect (VHT-MCS8 mode 11ac)
        status: active
        ieee80211: join xxxx chan 48 bssid f4:6b:ef:xx:xx:xx 61% wpakey wpaprotos wpa2 wpaakms psk wpaciphers ccmp wpagroupcipher ccmp`

Cool! There it is!

Autoselecting 2.4 GHz vs 5 GHz

I edited my /etc/hostname.iwm0 to stop it associating with the 5 GHz bssid and rebooted. When it came back, the adapter was talking to my WiFi AP with 802.11n on 2.4 GHz!

OK I was only upstairs from the WiFi AP and I still get a strongish signal on 5 GHz (61% as you could see above)

So I looked at some of the follow up commits about how it scans and such and saw this subsequent commit:

Log message: Fix wrongly implemented check for 5GHz access point RSSI threshold.

This check was wrong for drivers which report RSSI as a percentage, such as iwm(4) and iwx(4). Such drivers will now prefer 5GHz with 50% or greater RSSI, as was intended.`

Hmm.. OK. Maybe it just wanted to talk on 2.4 GHz. I put back in the bssid with 5 GHz for now because there’s so much interference on my 2.4 GHz bands here, that I get lots of latency spikes (pinging the WiFi AP the TTL varies between 10 ms and 985 ms!)

I need to do some more playing around to see what threshold it switches over to 5 GHz and when it goes back to 2.4 GHz.

Thanks so much to Stefan Sperling (stsp@) for his hard work on the wireless driver stack in OpenBSD!