Re: [PATCH] mac80211: check if channels allow 80 MHz for VHT probe requests

[Johannes Berg <johannes@sipsolutions.net>]

On Tue, 2014-11-25 at 19:00 +0800, YanBo wrote:
> On Tue, Nov 25, 2014 at 6:23 PM, Johannes Berg
> <johannes@sipsolutions.net> wrote:
> > From: Johannes Berg <johannes.berg@intel.com>
> >
> > If there are no channels allowing 80 MHz to be used, then the
> > station isn't really VHT capable even if the driver and device
> > support it in general. In this case, exclude the VHT capability
> > IE from probe request frames.
> >
> 
> FYI, there are some new devices could support the VHT even at 20Mhz
> band 2.4G mode.

So in 2.4 GHz we typically don't have VHT anyway - and realistically you
can't support real "VHT" there, you can only support the new
modulations. I think this will require some custom (vendor-specific)
advertisement though, since VHT advertisement implies 80 MHz support.

IOW, I think at this point this patch isn't a problem. If we really need
to support VHT modulations in 2.4 GHz (or even have devices that have
VHT modulation support, but no 80 MHz support in 5 GHz) then some new
advertisement will have to be done.

OTOH, you could argue for that advertisement that on 2.4 GHz you can
never do 80 MHz anyway - but can't you? In theory there's enough
spectrum for exactly one 80 MHz channel ...

johannes