Date: Thu, 9 Oct 2014 16:06:37 +0200
From: Karl Beldan <karl.beldan@gmail.com>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: linux-wireless <linux-wireless@vger.kernel.org>,
	Karl Beldan <karl.beldan@rivierawaves.com>
Subject: Re: [PATCH] mac80211/trivial: fix typo in starting baserate for
 rts_cts_rate_idx
Message-ID: <20141009140636.GC20644@magnum.frso.rivierawaves.com> (sfid-20141009_160644_475877_75FAC281)
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 <1412845586.1828.27.camel@jlt4.sipsolutions.net>
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On Thu, Oct 09, 2014 at 11:06:26AM +0200, Johannes Berg wrote:
> On Tue, 2014-10-07 at 15:53 +0200, Karl Beldan wrote:
> > From: Karl Beldan <karl.beldan@rivierawaves.com>
> 
> Is that really trivial? It seems to have some impact on the code, but I
> can't right now say exactly what the impact is. Can you describe it and
> say whether I should add it to mac80211 or mac80211-next? For "trivial"
> I'd probably say mac80211-next, but this might be more important than
> that?
> 
The typo is clearly showing but the faulty behavior clearly demands more
detail indeed.

It affects non-(V)HT rates and can lead to selecting an rts_cts rate
that is not a basic rate or way superior to the reference rate (ATM
rates[0] used for the 1st attempt of the protected frame data).
E.g, assuming the drivers register growing (bitrate) sorted
ieee80211_rate tables, having :
- rates[0].idx == d'2 and basic_rates == b'10100
will select rts_cts idx b'10011 & ~d'(BIT(2)-1), i.e. 1, likewise
- rates[0].idx == d'2 and basic_rates == b'10001 
will select rts_cts idx b'10000
The first is not a basic rate and the second is > rates[0].

I hope it clarifies things enough.
 
Karl