On 19 March 2014 15:22, Johannes Berg <johannes@xxxxxxxxxxxxxxxx> wrote: > 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? Correct. >> 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. Good point. Hostapd sets *both* HT Capability and HT Information IEs to "only 20Mhz" for VHT20. I can see Cisco EA6500 do the same thing too. >> 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? In case of AP mode you get ht_capa/vht_capa from userspace (i.e. hostapd). This would again imply hostapd does it wrong or is it perhaps the interface describing HT/VHT state is insufficient? Should mac80211 treat HT Capab and HT Info separately? Should they be passed and processed separately? Michał -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
