Could not connect to wpa_supplicant: wlan0 – re-trying

I work on embedded device and I am configuring the WLAN module (QCA6174 – ath10k driver) with wpa_supplicant.

• I load the driver modules (backports-20151120):

  insmod /lib/modules/3.10.65-b2196-h301/wlan/compat.ko; 
  insmod lib/modules/3.10.65-b2196-h301/wlan/cfg80211.ko; 
  insmod /lib/modules/3.10.65-b2196-h301/wlan/mac80211.ko; 
  insmod /lib/modules/3.10.65-b2196-h301/wlan/ath.ko; 
  insmod /lib/modules/3.10.65-b2196-h301/wlan/ath10k_core.ko skip_otp=y; 
  insmod /lib/modules/3.10.65-b2196-h301/wlan/ath10k_pci.ko
  

• I start the wpa_supplicant (default wpa_supplicant.conf):

  wpa_supplicant -dd -Dwext -i wlan0 -c /etc/wpa_supplicant/wpa_supplicant.conf -B
  
  [  182.257304] IPv6: ADDRCONF(NETDEV_CHANGE): wlan0: link becomes ready
  

everything seems to work fine. I see the wlan0 interface,I can scan with iwlist, /var/run/wpa_supplicant/wlan0 exist.

• But I can not use wpa_cli interface:

   #wpa_cli 
   wpa_cli v2.4
   Copyright (c) 2004-2015, Jouni Malinen <[e-mail]> and contributors
   Selected interface 'wlan0'
  
   Interactive mode
  
   Could not connect to wpa_supplicant: wlan0 - re-trying
  

Do you have any hints how can I track down the problem ?

Answer

After issuing

strace wpa_cli -i wlan0

the problem with /tmp folder was reported:

bind(3, {sa_family=AF_FILE, path="/tmp/wpa_ctrl_1095-5"}, 110) = -1 EROFS (Read-only file system)

After mounting tmpfs:

mount -t tmpfs -o size=12m tmpfs /tmp/

everything works fine.