[ath9k-devel] atheros chipset does not recover after going into unresponsive state

[Saurabh Chakrabarti <saurabh.chakrabarti@amideeptech.com>]

I am using TP-link WN721n usb wifi adapter with atheros 9271 chipset on 
raspberry pi. There are times when the wifi interface goes into an 
unresponsive state in which it does not send or receive any packets.

Here's the error log I get as soon as this occurs,

May 16 15:55:13 raspberry kernel: [  240.974619] ath: phy0: Timeout 
waiting for WMI command: WMI_REG_WRITE_CMDID
May 16 15:55:13 raspberry kernel: [  241.053067] ath: phy0: REGISTER 
WRITE FAILED:(0x4048, -110)
May 16 15:55:14 raspberry kernel: [  241.737670] ath: phy0: Dropping a 
packet due to TX timeout

When this state is hit, I reboot the system, but after reboot the wifi 
interface(wlan0) does not come back up. Here's the error I get on 
startup in the kernel log,

usb 1-1.2: device descriptor read/64, error -110

Interestingly, it works like a charm when I turn off the power and turn 
it back on(or if I pull the wifi adapter out and insert it back). But 
obviously I cannot do this all the time as the system is at a remote 
location.

Although I would want to know why the interface goes into this state, is 
there anything I can do so that I can atleast reset the interface once 
it goes into this state?

Regards,
Saurabh Chakrabarti