Re: [RFCv4 3/3] mac80211: add VHT support for IBSS

[Johannes Berg <johannes@sipsolutions.net>]

On Tue, 2015-01-27 at 09:44 +0100, Janusz Dziedzic wrote:

> +u8 *ieee80211_ie_build_vht_oper(u8 *pos, struct ieee80211_sta_vht_cap *vht_cap,
> +				const struct cfg80211_chan_def *chandef)

> +	/* 1 stream, MCS0-7 as a min Basic VHT MCS rates */
> +	vht_oper->basic_mcs_set = cpu_to_le16(0xfffc);

Unless I'm mistaken in my reading of the spec, this will make any
well-behaved client (i.e. not mac80211) not join this network since it
supports VHT MCSes.

We seem to do the same for HT:

        /* It seems that Basic MCS set and Supported MCS set
           are identical for the first 10 bytes */
        memset(&ht_oper->basic_set, 0, 16);
        memcpy(&ht_oper->basic_set, &ht_cap->mcs, 10);

but I'm not convinced it's right. It probably only works because nobody
ever tested against a well-behaved non-HT client? Or perhaps there isn't
even one?

I for one am not really comfortable with this restriction - there's very
little point in making such a restriction in IBSS since if you have it
then the other node will just form its own network on the same channel
and you've won nothing - only lost interoperability.

johannes