Problem in Linux with Alfa AWUS036ACHM where the device appears not to be initialized correctly on a reboot

[Brett Bergquist]

I am going to try to patch the driver.  My first cut will be to use
debugfs to see if I can do something that would reset the hardware as
if it was from a power on.   Anyone know of a datasheet or reference
manual for the Mediatek MT7610UN chip?  The chip is labeled

MEDIATEK
MT7610UN
2131-AMAL
FTPAR540


On Sat, Dec 7, 2024 at 1:59 PM Brett Bergquist
<bbergquist at epc-instore.com> wrote:
>
> I have a product that is built using Yocto Kirkstone release (Kernel
> version 5.15) that uses the Alfa AWUS036ACHM product.  It is working
> most of the time but I have a strange situation.  If I reboot the
> system, there will come a time where the device is detected but it
> does not work.  This is using systemd-networkd for networking and
> using wpa_supplicant.
>
> To stress the system, I am externally logging into the system and
> rebooting.  This might be successful for a number of iterations, I
> have seen 30 reboots.  Eventually however the networking will fail
> with wpa_supplicant not progressing at all.  I connect a console cable
> to observe what I see.
>
> When in this state, the USB device is seen, the modules loaded look like
> >
> > root at 9998:~# lsmod
> > Module                  Size  Used by
> > mt76x0u                16384  0
> > mt76x0_common          40960  1 mt76x0u
> > mt76x02_usb            20480  1 mt76x0u
> > mt76_usb               28672  2 mt76x02_usb,mt76x0u
> > mt76x02_lib            61440  3 mt76x02_usb,mt76x0_common,mt76x0u
> > mt76                   57344  5 mt76_usb,mt76x02_lib,mt76x02_usb,mt76x0_common,mt76x0u
>
> Everything looks normal.   However the wifi does not work.  Using "iw
> dev wlan0 station dump" and nothing is seen.  I have so far found
> nothing that I can do in software that will reliably get wifi out of
> this state.   I have tried
>
> delaying starting wpa_supplicant for a bit (30 seconds) after boot on
> the theory to let the USB bits in the kernel settle
> reset the USB port and restart the wpa_supplicant
> unbind and rebind the USB device and restart the wpa_supplicant
> unload the driver kernel module and reload the driver kernel module
> and restart the wpa_supplicant
>
> Even a reboot of the system will not recover once in this state.  I
> can recover by unplugging the wifi device USB connection and replug it
> back in and then restart wpa_supplicant and the networking comes right
> up.  A reboot likely does not cause loss of power to the wifi device.
>  I can also recover by a complete power off/power on of the system.
>
> It is as if the wifi device gets into some state that is not good and
> cannot be cleared in software.  I have also seen the device get into a
> state where it appears connected but only partially in that I can pass
> things such as ICMP ECHO to and from the system, but I cannot pass
> data, as an example SSH into our out of the system starts but hangs.
> Using Wireshark I can see the TCP connection being established with
> the SYN, SYN/ACK, ACK handshake but then start of the SSH setup fails
> and times out.   Again, simply unplug and replug the wifi device and
> it works.
>
> Note that this occurs on multiple wifi devices which I have used with
> the same system and also the same wifi device on a different system.
> After a number of reboots I can get into this state.
>
> So my question is if that type of thing has been seen and possibly
> corrected in a later kernel version.  I would then attempt to backport
> changes as needed.
>
>
> --
> Brett M. Bergquist
> Distinguished Member Technical Staff
> EntryPoint Communications LLC
> 30 Waterside Drive, Suite 100
> Farmington, CT 06032
>
> Phone: (203) 206 3542
> Email: bbergquist at epc-instore.com
>
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