Re: [PATCH] mac80211: don't downgrade VHT20 to HT20

[Johannes Berg <johannes@sipsolutions.net>]

Sorry for the delay. Somehow I thought this was addressed, but I'm
confused.

I think we all agree that the spec says:

> > A VHT STA shall set the Supported Channel Width Set subfield in its HT
> > Capabilities element HT Capabilities Info field to 1, indicating that
> > both 20 MHz operation and 40 MHz operation are supported.

and that the station should therefore set the 20_40 capability bit in
the association response?

> The spec also defines VHT BSS operating channel width is derived from
> HT Operation Element: STA Channel Width field (Table 10-19) and 20 MHz
> is not forbidden for AP/mesh. hostapd seems to go in line with this
> and allows VHT20 and VHT40.

Yes but how is that related to the *capability* bit? You're talking
about the HT/VHT operation information.

> Without my patch (i.e. with the 20/40 check left intact):
> 
> * If a station connects to VHT20 BSS, hostapd tries to add a VHT20
> station, but mac80211 downgrades it to HT20,
> * If mac80211 station connects to a VHT20 BSS it gets downgraded to HT20 too.
> 
> This means mac80211 is unable to setup VHT20 pairing properly even
> though VHT20 BSS is defined in the spec.
> 
> My take is 10.39.1 means VHT STA AssocReq must contain
> IEEE80211_HT_CAP_SUP_WIDTH_20_40.
> I suppose AP (hostapd) should deny STA association in that case.

So are you saying the station isn't setting 20_40 capability? Or is
something else unsetting the bit in case it's a 20MHz network?

johannes