[PATCH] hw_features: clean center freq for falling back ht40 channels

Jouni Malinen j at w1.fi
Sun Feb 5 11:16:39 PST 2017

On Mon, Jan 30, 2017 at 11:20:14AM +0100, Eduardo Abinader wrote:
>  The scenario is very specific: I have both ieee80211n=1 and
> ieee80211ac=1 also with ht_capab and vht_capab both set. Here is some
> log;

>  HT40: control channel: 161  secondary channel: 165
>  HT40 channel pair (161, 165) not allowed
>  Fallback to 20 MHz

What is this configuration trying to do? There is no 40 MHz channel
defined with primary channel on 161 and secondary on 165..

>  Completing interface initialization
>  Mode: IEEE 802.11a  Channel: 161  Frequency: 5805 MHz
>  DFS chan_idx seems wrong; num-ch: 25 ch-no: -6 conf-ch-no: 161 11n: 1
> sec-ch: 0 vht-oper-width: 1

And this is furthermore configured to enable 80 MHz VHT? How is that
supposed to work here? What vht_oper_centr_freq_seg0_idx value is used?

> Interface initialization failed
>  wlp2s0: interface state HT_SCAN->DISABLED
>  wlp2s0: AP-DISABLED

And does this actually work in some manner for you with this patch
applied? I cannot reproduce such behavior, i.e., the failure happens
here regardless of whether the patch is applied or not..

Can you please share the full configuration parameters for setting this
channel and a debug log from a case where the patch is applied and
behavior changes to something that could be claimed to be useful?

IMHO, there is not really much hostapd should do with such configuration
apart from potentially rejecting it even before trying to do a 40 MHz
co-ex scan..

Jouni Malinen                                            PGP id EFC895FA

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