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From:   Daniel Lenski <dlenski@gmail.com>
Date:   Sun, 30 Jun 2019 14:56:09 -0700
Message-ID: <CAOw_LSF5kBQCECi+1waXNMvuo+eT68fr9SO52JMuVrLtq8_CLg@mail.gmail.com>
Subject: Fwd: rtl8723au: WiFi scanning stops working shortly after driver loads?
To:     linux-wireless@vger.kernel.org
Cc:     Jes Sorensen <Jes.Sorensen@redhat.com>
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Sender: linux-wireless-owner@vger.kernel.org
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Hi,
I recently started to use an older laptop with RTL8723AU
WiFi/Bluetooth again for the first time in a couple years.

I've noticed a strange behavior of this device/driver (rtl8xxxu with
4.4.0 kernel): the ability to do a WiFi scan *while associated with an
access point* somehow disappears ~30 seconds after the driver is
loaded.

That is, right after loading the module and connecting to a WiFi
network, I can successfully do `iwlist wlan0 scan`; but after a short
period of time, the scan stops returning any results other than for
the AP that I'm already connected to. Disconnecting from the AP
"resets" this behavior, but once I reconnect to a network, my ability
to scan disappears again shortly thereafter.

Steps to reproduce:

    # rmmod rtl8xxxu
    # modprobe rtl8xxxu debug=99
    # while true; do sudo iwlist wlan0 scan | grep ESSID | wc -l ; sleep 2; done
    13
    13
    13
    13
    1     # only my current AP
    1
    ...

Is this a known issue with the hardware, or with the driver? Any
advice on how to debug it? I've looked through the debug messages, and
found nothing that seems to indicate a state change around the time
that the scan stops working.

Thanks,
Dan

ps: I'm using the "standard" rtl8723aufw_B_NoBT.bin firmware
(https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/tree/rtlwifi/rtl8723aufw_B_NoBT.bin)
and have loaded *only* the WiFi driver, *not* the Bluetooth driver.

[ 3110.201258] usb 1-1.4: Vendor: Realtek
[ 3110.201267] usb 1-1.4: Product: 802.11n WLAN Adapter
[ 3110.201274] usb 1-1.4: RTL8723AU rev B (TSMC) 1T1R, TX queues 2,
WiFi=1, BT=1, GPS=0, HI PA=0
[ 3110.201279] usb 1-1.4: RTL8723AU MAC: 20:16:d8:ce:5e:29
[ 3110.201284] usb 1-1.4: rtl8xxxu: Loading firmware
rtlwifi/rtl8723aufw_B_NoBT.bin
[ 3110.201355] usb 1-1.4: Firmware revision 31.0 (signature 0x2302)