From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Berg Subject: Re: "Overall" and per-chain signal/noise values (was Re: multi-antenna handling) Date: Tue, 15 Jan 2019 14:19:40 +0100 Message-ID: <314bf4573f84bf0df673e94e4e085522cce10fcd.camel@sipsolutions.net> References: <1345481425.4459.46.camel@jlt3.sipsolutions.net> <1373273952.8312.7.camel@jlt4.sipsolutions.net> <1403679889.4140.2.camel@jlt4.sipsolutions.net> <20140625090901.fa121a689f823f3af1db1e3a@lm7.fr> <1403709105.4140.13.camel@jlt4.sipsolutions.net> <636CB894-79D9-4CC3-B820-833761A9666D@alum.mit.edu> <1403763600.4131.3.camel@jlt4.sipsolutions.net> <0836AF8F-37B1-4E52-B14C-7D7B31D4C5E8@alum.mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <0836AF8F-37B1-4E52-B14C-7D7B31D4C5E8-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org> Sender: radiotap-owner-sUITvd46vNxg9hUCZPvPmw@public.gmane.org List-Unsubscribe: To: Guy Harris Cc: Matteo Cypriani , Felix Fietkau , "radiotap-sUITvd46vNxg9hUCZPvPmw@public.gmane.org" List-Id: radiotap@radiotap.org On Sun, 2018-12-30 at 13:47 -0800, Guy Harris wrote: > On Jun 25, 2014, at 11:20 PM, Johannes Berg wrote: > > > We actually have one per-chain value, and one "overall" value, the > > latter is what we report in the first radiotap namespace, the per-chain > > ones in the latter namespaces that only have the signal and antenna > > value (but obviously we could add anything else that made sense per > > antenna) > > > > Maybe we shouldn't be reporting the "overall" value? The calculation of > > that seems to be driver dependent, our (the Intel) driver just takes the > > max. If ath9k has a more specific calculation then I can see how that's > > a bit confusing but OTOH it actually reports what much else of the stack > > used for further work. > > About 4 1/2 years later, the ath9k driver plus the mac80211 code > appears to provide the "overall" strength plus per-antenna strengths, > at least as of the 4.17.10 kernel, so I guess it's somewhat of a *de > facto* standard that there's an "overall" value. I suppose you could argue that. The per-chain signals are actually optional for drivers to provide, but the overall signal strength (which, btw, isn't defined how this is derived from the per-chain signals if at all) is more or less necessary for proper operation (roaming, ...) > Given that, this is probably worth documenting - but not requiring, in > case some adapter+driver combination doesn't supply it. > > Presumably the description would be that: > > if you see a signal strength indication, and *don't* see an > antenna number before the end of the header or a Radiotap Namespace > field, it's an "overall" value; > > otherwise, it's a per-antenna value for the specified antenna. > > Parsers must not assume that there will or won't be an "overall" value > if there are per-antenna values. > > The "overall" value for a multi-antenna receiver could be described as > device-dependent, which might suggest that, unless you know the > device, you shouldn't try to interpret it. Makes sense. Want to update the github docs? johannes