Re: [PATCH 0/8] Add support for 5 and 10 MHz channels

From: Simon Wunderlich <simon.wunderlich@s2003.tu-chemnitz.de>
To: Adrian Chadd <adrian@freebsd.org>
Cc: Johannes Berg <johannes@sipsolutions.net>,
	linux-wireless@vger.kernel.org,
	Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de>,
	Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Subject: Re: [PATCH 0/8] Add support for 5 and 10 MHz channels
Date: Fri, 10 May 2013 11:32:41 +0200	[thread overview]
Message-ID: <20130510093241.GA28714@pandem0nium> (raw)
In-Reply-To: <CAJ-Vmo=RCVOD1ffraTexETgqYP6LbLAa_g0d2DVd8yTO99Q1AQ@mail.gmail.com>

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Hey,

On Fri, May 10, 2013 at 02:12:00AM -0700, Adrian Chadd wrote:
> On 10 May 2013 00:26, Johannes Berg <johannes@sipsolutions.net> wrote:
> > On Thu, 2013-05-09 at 20:10 +0200, a@pandem0nium wrote:
> >
> >> Comments:
> >>  * Is there any special requirement for handling beacons? For example,
> >>    rates are halfed or quartered, but some rates could not be represented
> >>    in the rate IEs. For example, 2.25 mbit/s can not be represented as
> >>    multiple of 500 kbps.
> >>  * therefore, all rates are handled like the corresponding 20 MHz
> >> rates
> >>    internally, which makes a lot of things easier (no changes required
> >>    for rc-algos, beacon creation, etc...). We might consider adjusting
> >> the
> >>    output of rates for nl80211 or radiotap, though.
> >
> > This seems completely wrong, since Clause 18 says:
> >
> >         The OFDM system also provides a “half-clocked” operation using
> >         10 MHz channel spacings with data communications capabilities of
> >         3, 4.5, 6, 9, 12, 18, 24, and 27 Mb/s. The support of
> >         transmitting and receiving at data rates of 3, 6, and 12 Mb/s is
> >         mandatory when using 10 MHz channel spacing. The half-clocked
> >         operation doubles symbol times and clear channel assessment
> >         (CCA) times when using 10 MHz channel spacing. The regulatory
> >         requirements and information regarding use of this OFDM PHY are
> >         in Annex D and Annex E.
> >
> > IOW, it treats the rates as actually the rate they should be. Besides,
> > what's so hard about rounding up? (8.4.2.4)
> >
> >         and bits 6 to 0 are set to the data rate, if necessary rounded
> >         up to the next 500kb/s, in units of 500 kb/s.
> >
> >
> > I also think you really need to handle this. If you just want a hack for
> > 5/10 MHz, you can put it into drivers' debugfs, if not, then it should
> > be done properly :-)
> 
> I think net80211 from FreeBSD and madwifi do this. Ie, they advertise
> the half and quarter rate speeds as their real speeds at half/quarter
> rate.

Ah, OK.

> 
> If anything, interoperability would be nice.

Yes interoperability would be nice of course - I'll re-work the patchset
to use the according half and quarter rates. Meanwhile, what do you guys think
about enabling HT too?

Cheers,
	Simon
> 
> 
> 
> 
> Adrian

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