Re: [PATCH 2/2] wireless: return correct mandatory rates

[Simon Wunderlich <sw@simonwunderlich.de>]

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Hi,

On Friday, September 8, 2017 10:53:37 AM CEST Richard Schütz wrote:
> Am 08.09.2017 um 10:43 schrieb Richard Schütz:
> > Am 08.09.2017 um 08:55 schrieb Johannes Berg:
> >> On Thu, 2017-09-07 at 17:47 +0200, Richard Schütz 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.
> >> 
> >> This I don't understand - what "comparison" are you talking about?
> > 
> > Sorry, I meant the condition that checks for the presence of
> > mandatory_flag at the bottom of the function.
> > 
> >>> 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).
> >> 
> >> 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.
> > 
> > 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.
> 
> Looks like the old address is invalid now. New try.
> 

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

However, technically, the Qualcomm/Atheros hardware (ath9k and ath5k) supports 
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 
when we follow the standard strictly. The question is if we should follow the 
standard strictly - this feature is already quite limited, and people tend to 
use the ath9k/ath5k chanbw patch from OpenWRT/LEDE.

Cheers,
      Simon

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