From: Simon Wunderlich <sw@simonwunderlich.de>
To: Richard =?ISO-8859-1?Q?Sch=FCtz?= <rschuetz@uni-koblenz.de>
Cc: Johannes Berg <johannes@sipsolutions.net>,
        linux-wireless@vger.kernel.org
Subject: Re: [PATCH 2/2] wireless: return correct mandatory rates
Date: Fri, 08 Sep 2017 11:33:32 +0200
Message-ID: <5435234.Pp2Z8V5qmG@prime> (sfid-20170908_114046_778491_3C0F0D92)
In-Reply-To: <1f7e466e-2a68-b97a-ee2e-21c3e74a9fc5@uni-koblenz.de>
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Hi,

On Friday, September 8, 2017 10:53:37 AM CEST Richard Sch=FCtz wrote:
> Am 08.09.2017 um 10:43 schrieb Richard Sch=FCtz:
> > Am 08.09.2017 um 08:55 schrieb Johannes Berg:
> >> On Thu, 2017-09-07 at 17:47 +0200, Richard Sch=FCtz wrote:
> >>> Use IEEE80211_RATE_MANDATORY_G instead of IEEE80211_RATE_MANDATORY_B
> >>> for comparison to get all mandatory rates in 2.4 GHz band. It is safe
> >>> to do so because ERP mandatory rates are a superset of HR/DSSS
> >>> mandatory rates.
> >>=20
> >> This I don't understand - what "comparison" are you talking about?
> >=20
> > Sorry, I meant the condition that checks for the presence of
> > mandatory_flag at the bottom of the function.
> >=20
> >>> Also force IEEE80211_RATE_MANDATORY_A for 10 MHz and 5 MHz channels
> >>> as they use "half-clocked" respectively "quarter-clocked" operation
> >>> of the OFDM rates (IEEE Std 802.11-2016, 17.1.1).
> >>=20
> >> I don't think this is correct - the way the flags are used, anything on
> >> 2.4 GHz would never bother to check the MANDATORY_A flag.
> >=20
> > Do we actually allow 10 MHz and 5 MHz operation in the 2.4 GHz band? As
> > far as I can tell that has only been specified for OFDM PHYs, which use
> > the 5 GHz band and are covered by IEEE80211_RATE_MANDATORY_A, but I am
> > not a hundred per cent sure about that. Cc'ing Simon Wunderlich who
> > originally implemented checking of scan_width here.
>=20
> Looks like the old address is invalid now. New try.
>=20

Yeah, officially only OFDM has the half/quarter clock stuff defined, not ER=
P (2.4=20
GHz 11g) or DSSS, and also not HT.

However, technically, the Qualcomm/Atheros hardware (ath9k and ath5k) suppo=
rts=20
DSSS or HT on quarter and half rates just fine, also on 2.4 GHz.

I believe we currently support the 5/10 MHz on 2.4 GHz, although we shouldn=
't=20
when we follow the standard strictly. The question is if we should follow t=
he=20
standard strictly - this feature is already quite limited, and people tend =
to=20
use the ath9k/ath5k chanbw patch from OpenWRT/LEDE.

Cheers,
      Simon
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