Subject: RE: mac80211 20/40 coexist
From: Johannes Berg <johannes@sipsolutions.net>
To: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Cc: "Manoharan, Rajkumar" <rmanohar@qca.qualcomm.com>,
	linux-wireless <linux-wireless@vger.kernel.org>
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Date: Mon, 19 Mar 2012 09:23:32 +0100
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On Mon, 2012-03-19 at 08:25 +0530, Sujith Manoharan wrote:
> Johannes Berg wrote:
> > I'm not sure I can believe this -- surely the firmware has to have a way
> > of dealing with stations that can't do 40 MHz and stations that can, so
> > switching between the two doesn't seem like a major proposal? We also
> > don't currently handle the action frames for that, but it seems like we
> > should.
> 
> We have BSS_CHANGED_HT for doing this.

Actually, no -- that's how we got into this mess to start with :-)
Bandwidth here is a per-peer property, BSS_CHANGED_HT is changing the
operation mode (things like non-HT protection).

We used to change the channel bandwidth when the AP wanted to only
receive 20 MHz, but that seems like a bug because that doesn't even
necessarily mean it wants to TX 20 MHz.

So I think what Paul and I have changed/are changing it to makes more
sense:
 * the channel bandwidth never changes
 * the RX bandwidth for a peer has its own notification
 * BSS_CHANGED_HT changes protection mode etc.

johannes