[PATCH] ACS: fix VHT20

Jouni Malinen j
Sat Mar 15 08:32:21 PDT 2014

On Sat, Mar 15, 2014 at 03:34:40PM +0100, Johannes Berg wrote:
> No, there's no objection to that change - that part is certainly
> correct. This just triggered my memory of the other patch that you
> recently applied, allowing the field to be set to zero in the IEs.

OK, thanks.

> Yeah, pretty much. I sent you (and you applied) a patch that was
> allowing to set it to 0 in the config file instead, which is technically
> required for spec compliance (field is reserved in 20/40 MHz case), but
> in practice interoperability may be better with the field getting set,
> particularly with old broken mac80211 ;-)

So it may actually be fine to leave this as-is and allow configuration
to be used to select whether to comply with the reserved=0 requirement..

> > I agree that these fields seems to be marked Reserved in IEEE Std
> > 802.11ac-2013 for this case and per IEEE Std 802.11-2014, reserved
> > fields/subfields are set to 0 upon transmission.
> 802.11-2014? I guess I need to find that.

Good luck finding that.. :)  That was supposed to be -2012.

> > Does setting this field to 0 cause interop issues with earlier
> > implementations before that "recent patch" mentioned above? (And if so,
> > do we care?)
> It does, setting it to 0 means that mac80211 until commit cb664981607a
> ("mac80211: fix association to 20/40 MHz VHT networks") will connect as
> an HT client, and ignore VHT. We probably shouldn't care though, and
> it's not a major issue (HT connection still works fine.)

OK, I was assuming don't care, but this sounds like it is even less of
an issue that I thought.

Jouni Malinen                                            PGP id EFC895FA

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