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From:   Ramon Fontes <ramonreisfontes@gmail.com>
Date:   Tue, 27 Aug 2019 09:06:11 -0300
Message-ID: <CAK8U23biuUY9hWE1NOnSbJCRtRVfdg1a27ZOkU5cbaGdzZLYEA@mail.gmail.com>
Subject: mac80211_hwsim (kernel 4.18+): wmediumd + 2.4Ghz
To:     linux-wireless@vger.kernel.org
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Sender: linux-wireless-owner@vger.kernel.org
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Hello,

When I use 2.4Ghz band with -only one- AP (running on top of hostapd)
I get a (additional) list of frequencies at 5Ghz. When I do "iw dev ..
scan"

BSS 02:00:00:00:04:00(on sta1-wlan0) -- associated
TSF: 1566905272877856 usec (18135d, 11:27:52)
freq: 2422
beacon interval: 100 TUs
capability: ESS ShortSlotTime (0x0401)
signal: -34.00 dBm
last seen: 0 ms ago
Information elements from Probe Response frame:
SSID: simplewifi
Supported rates: 1.0* 2.0* 5.5* 11.0* 6.0 9.0 12.0 18.0
DS Parameter set: channel 3
ERP: Barker_Preamble_Mode
Extended supported rates: 24.0 36.0 48.0 54.0
Extended capabilities:
* Extended Channel Switching
* Multiple BSSID
* SSID List
* Operating Mode Notification

BSS 02:00:00:00:04:00(on sta1-wlan0)
TSF: 1566905274269230 usec (18135d, 11:27:54)
freq: 5180
beacon interval: 100 TUs
capability: ESS ShortSlotTime (0x0401)
signal: -34.00 dBm
last seen: 0 ms ago
Information elements from Probe Response frame:
SSID: simplewifi
Supported rates: 1.0* 2.0* 5.5* 11.0* 6.0 9.0 12.0 18.0
DS Parameter set: channel 3
...

BSS 02:00:00:00:04:00(on sta1-wlan0)
TSF: 1566905274269230 usec (18135d, 11:27:54)
freq: 5200
beacon interval: 100 TUs
capability: ESS ShortSlotTime (0x0401)
signal: -34.00 dBm
last seen: 0 ms ago
Information elements from Probe Response frame:
SSID: simplewifi
Supported rates: 1.0* 2.0* 5.5* 11.0* 6.0 9.0 12.0 18.0
DS Parameter set: channel 3
...

and so on (please notice that channel number and frequency)..
iw dev scan returns all the 5Ghz frequencies defined in
https://github.com/torvalds/linux/blob/master/drivers/net/wireless/mac80211_hwsim.c#L328
It happens only when wmediumd is being used. When hostapd is running
with 5Ghz it seems to work as expected, since iw returns only the AP
running at 5Ghz. In other words, the problem occurs only when hostapd
is running at 2.4Ghz.

I noticed that it happens from kernel 4.18. If I comment
https://github.com/torvalds/linux/blob/b55f3b841099e641bdb2701d361a4c304e2dbd6f/drivers/net/wireless/mac80211_hwsim.c#L2838,
iw returns only 2422Mhz. However, I couldn't find the reason for such
problem.

There could be some problem with mac80211_hwsim, or am I missing something here?

Best Regards,
Ramon Fontes