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From:   Krishna Chaitanya <chaitanya.mgit@gmail.com>
Date:   Wed, 11 Dec 2019 18:50:46 +0530
Message-ID: <CABPxzY+BCcjFvQtPPdeBBOY1zcXzVd23GsSPKbd5BRsKRsTeog@mail.gmail.com>
Subject: Re: Correct radiotap header for 802.11ad
To:     Johannes Berg <johannes@sipsolutions.net>
Cc:     Guy Harris <guy@alum.mit.edu>,
        "radiotap@netbsd.org" <radiotap@netbsd.org>,
        Simon Barber <simon@superduper.net>,
        Richard Sharpe <realrichardsharpe@gmail.com>,
        linux-wireless <linux-wireless@vger.kernel.org>,
        Maya Erez <merez@codeaurora.org>, wil6210@qti.qualcomm.com
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On Wed, Dec 11, 2019 at 6:28 PM Johannes Berg <johannes@sipsolutions.net> wrote:
>
> On Wed, 2019-12-11 at 15:09 +0530, Krishna Chaitanya wrote:
> >
> > > For both the Linux userspace reporting and radiotap then, this
> > > completely ignores the existence of the MCSes 9.1 and 12.1-12.6, which
> > > cannot be captured in either format right now. Maybe the extended SC
> > > MCSes are just not used by equipment in the field?
> > >
> > They are used. Unfortunately, Linux-wireless doesn't have native support for DMG
> > wil6210 and our driver has to workaround by using HT IE's
> > (ieee80211_supported_band).
>
> You make it sound like that some sort of thing that Linux cannot really
> do better. That's far from the truth! We keep extending this (HT, VHT,
> HE recently) and there's no fundamental reason we couldn't do extensions
> for DMG. It's just that nobody who actually has a driver for Linux
> bothered doing so!
Sorry, that wasn't my intent, as there is a single upstream driver I guess
it was easier to workaround than to properly add support. I agree that
it shouldn't
be hard, may be we can do it properly for 11ay.
> > > In any case, to capture DMG properly I'd say we need a new radiotap
> > > field with at least
> > >  * (base) MCS
> > >  * Extended SC MCS bit
> > > and it should probably optionally cover the other possible fields as
> > > well
> > >  * Scrambler Initialization
> > >  * Length (?)
> > >  * Additional PPDU bit
> > >  * PPDU type bit
> > >  * Training Length
> > >  * Beam Tracking Request
> > >  * Last RSSI
> > >  * Turnaround
> > yes, we definitely need this, there are some additional fields in
> > 11ay, but I guess that
> > discussion is for another time.
>
> Somebody (@QCA I guess, I don't have any functioning driver/hardware for
> Linux for this) really should sit down and define the extensions to
> cfg80211/nl80211 to capture the data properly, and a radiotap extension.
> None of that is hard, I've done it for VHT before and HE recently.