Hello,

On Sunday, February 28, 2016 03:06:35 AM alexander nekrasov wrote:

I'm using TP-LINK TL-WN821N and encountering very annoying behaviour -
adapter 'hangs' at random period of time - sometimes it is 1 hour,
sometimes 2. After it hangs Network manager does not see any wireless
networks and the only way to make it work is to reboot system (also
tried unplugging/plugging adapter and removing/adding module but it
did not work)

Did it get hot? Or Have you tried unloading/reloading the ohci/ehci/xhci?
The used USB-PHY FUSB200 (in the AR9170) is known to misbehave. If you
want to read more about the implications and possible solution, you can
visit the ath9k_htc firmware community. They have written a wiki entry
which describes the issues in detail [0].
 

Heres lsusb -v:
Bus 004 Device 004: ID 0cf3:1002 Atheros Communications, Inc. TP-Link
TL-WN821N v2 / TL-WN822N v1 802.11n [Atheros AR9170]

And here what i have in syslog right before the hang:
Following messages are also relevant to adapter failure but i guess it
will be to long to post it here.

Feb 28 01:46:53 evren kernel: [ 4978.753087] usb 4-1.4: no command
feedback received (-90).
Feb 28 01:46:53 evren kernel: [ 4978.753098] usb 4-1.4: restart device (6)
Feb 28 01:46:54 evren kernel: [ 4979.891093] usb 4-1.4: device
restarted successfully.
Feb 28 01:46:54 evren kernel: [ 4979.899273] ieee80211 phy1: Hardware
restart was requested

Commands are issued on the devices end point #4.... And the response the
driver is waiting for doesn't get through. If you want to debug this, 
you'll need to look at the usb data stream and check which party (host
controller (ehci/ohci), device (AR9170) or cable?) is at fault. 

Regards,
Christian

[0] <https://github.com/qca/open-ath9k-htc-firmware/wiki/usb-related-issues>