Hi,

When I set "SHORT-GI-20" in the /etc/config/wireless, the wifi just can't start and I got message of:
"Driver does not support configured HT capability [SHORT-GI-20]"

Just wonder is this a bug or I am missing some configration?

I am using WR741 with trunk version r31151, the wireless driver used is ath9k, and I believe this problem exist in the earlier verison as well.

The problem I have is not only can't set this parameter, but also when I have a STA which can only support SGI 20 will not able to connect to the AP.

Thanks for any suggestions.

BRs
Kerry

Well thats probably because the driver does not support the configured HT capability

Seriously, the reason is written there, in plain sight - short guard intervals are not implemented in the driver.
Why do you conclude there must be a bug or problem?
Did you check "iw" and see SHORT-GI in the wiphy capabilities?
Or did you just copy-paste random stuff from the internet?

Thanks for the answer.
Well, the actual problem is that one of my STA has only the capability of handling HT SHORT-GI-20, and from the debug log file from hostapd, the negotiation result is set the HT Cap. to 0x2C (see the log below), which indicate the short-gi-20 supported by hostapd. But unfortunately the driver doesn't support the short-gi-20. So the result is that the STA is not able to successfully complete the 4-way handshake with the AP.

So I think either the driver shall support short-gi-20 or the hostapd shall negotiate with the STA not to use SHORT-GI-20 if the driver doesn't support it. Might be bug in hostapd if the driver really can't support SGI-20.

Here I attached some log from hostapd:
==================================
......
authentication: STA=20:59:a0:3c:42:c4 auth_alg=0 auth_transaction=1 status_code=0 wep=0
  New STA
wlan0: STA 20:59:a0:3c:42:c4 IEEE 802.11: authentication OK (open system)
wlan0: STA 20:59:a0:3c:42:c4 MLME: MLME-AUTHENTICATE.indication(20:59:a0:3c:42:c4, OPEN_SYSTEM)
wlan0: STA 20:59:a0:3c:42:c4 MLME: MLME-DELETEKEYS.request(20:59:a0:3c:42:c4)
authentication reply: STA=20:59:a0:3c:42:c4 auth_alg=0 auth_transaction=2 resp=0 (IE len=0)
wlan0: Event TX_STATUS (18) received
wlan0: Event TX_STATUS (18) received
mgmt::auth cb
wlan0: STA 20:59:a0:3c:42:c4 IEEE 802.11: authenticated
wlan0: Event RX_MGMT (20) received
mgmt::assoc_req
association request: STA=20:59:a0:3c:42:c4 capab_info=0x411 listen_interval=3
Validating WMM IE: OUI 00:50:f2  OUI type 2  OUI sub-type 0  version 1  QoS info 0x0
  new AID 1
nl80211: Set beacon (beacon_set=1)
HT: STA 20:59:a0:3c:42:c4 HT Capabilities Info: 0x002c
update_sta_ht STA 20:59:a0:3c:42:c4 - no greenfield, num of non-gf stations 1
update_sta_ht STA 20:59:a0:3c:42:c4 - 20 MHz HT, num of 20MHz HT STAs 1
hostapd_ht_operation_update current operation mode=0x0
hostapd_ht_operation_update new operation mode=0x6 changes=2
nl80211: Set beacon (beacon_set=1)
wlan0: STA 20:59:a0:3c:42:c4 IEEE 802.11: association OK (aid 1)
wlan0: Event TX_STATUS (18) received
mgmt::assoc_resp cb
wlan0: STA 20:59:a0:3c:42:c4 IEEE 802.11: associated (aid 1)
wlan0: STA 20:59:a0:3c:42:c4 MLME: MLME-ASSOCIATE.indication(20:59:a0:3c:42:c4)
wlan0: STA 20:59:a0:3c:42:c4 MLME: MLME-DELETEKEYS.request(20:59:a0:3c:42:c4)
wpa_driver_nl80211_set_key: ifindex=9 alg=0 addr=0x715fa0 key_idx=0 set_tx=1 seq_len=0 key_len=0
   addr=20:59:a0:3c:42:c4
wlan0: STA 20:59:a0:3c:42:c4 WPA: event 1 notification
wpa_driver_nl80211_set_key: ifindex=9 alg=0 addr=0x715fa0 key_idx=0 set_tx=1 seq_len=0 key_len=0
   addr=20:59:a0:3c:42:c4
IEEE 802.1X: Ignore STA - 802.1X not enabled or forced for WPS
wlan0: STA 20:59:a0:3c:42:c4 WPA: start authentication
WPA: 20:59:a0:3c:42:c4 WPA_PTK entering state INITIALIZE
wpa_driver_nl80211_set_key: ifindex=9 alg=0 addr=0x715fa0 key_idx=0 set_tx=1 seq_len=0 key_len=0
   addr=20:59:a0:3c:42:c4
wlan0: STA 20:59:a0:3c:42:c4 IEEE 802.1X: unauthorizing port
WPA: 20:59:a0:3c:42:c4 WPA_PTK_GROUP entering state IDLE
WPA: 20:59:a0:3c:42:c4 WPA_PTK entering state AUTHENTICATION
WPA: 20:59:a0:3c:42:c4 WPA_PTK entering state AUTHENTICATION2
WPA: Re-initialize GMK/Counter on first station
GMK - hexdump(len=32): [REMOVED]
Key Counter - hexdump(len=32): [REMOVED]
GTK - hexdump(len=16): [REMOVED]
wpa_driver_nl80211_set_key: ifindex=9 alg=3 addr=0x455a24 key_idx=1 set_tx=1 seq_len=0 key_len=16
   broadcast key
WPA: Assign ANonce - hexdump(len=32): 9f 59 3e ea 67 63 0e 40 8a 41 9d f4 e4 4a 3a 5f 02 00 bd e4 93 b6 bc f4 4f 1c f3 f3 d7 bd 29 ae
WPA: 20:59:a0:3c:42:c4 WPA_PTK entering state INITPSK
WPA: 20:59:a0:3c:42:c4 WPA_PTK entering state PTKSTART
wlan0: STA 20:59:a0:3c:42:c4 WPA: sending 1/4 msg of 4-Way Handshake
WPA: Send EAPOL(version=2 secure=0 mic=0 ack=1 install=0 pairwise=8 kde_len=0 keyidx=0 encr=0)
WPA: Use EAPOL-Key timeout of 100 ms (retry counter 1)
nl80211: Event message available
nl80211: New station 20:59:a0:3c:42:c4
wlan0: Event TX_STATUS (18) received
wlan0: STA 20:59:a0:3c:42:c4 WPA: EAPOL-Key timeout
WPA: 20:59:a0:3c:42:c4 WPA_PTK entering state PTKSTART
wlan0: STA 20:59:a0:3c:42:c4 WPA: sending 1/4 msg of 4-Way Handshake
WPA: Send EAPOL(version=2 secure=0 mic=0 ack=1 install=0 pairwise=8 kde_len=0 keyidx=0 encr=0)
WPA: Use EAPOL-Key timeout of 1000 ms (retry counter 2)
......
=================================
Also the"iw list" for the driver info:

root@OpenWrt:~# iw list
Wiphy phy0
        Band 1:
                Capabilities: 0x11ce
                        HT20/HT40
                        SM Power Save disabled
                        RX HT40 SGI
                        TX STBC
                        RX STBC 1-stream
                        Max AMSDU length: 3839 bytes
                        DSSS/CCK HT40
                Maximum RX AMPDU length 65535 bytes (exponent: 0x003)
                Minimum RX AMPDU time spacing: 8 usec (0x06)
                HT TX/RX MCS rate indexes supported: 0-7
                Frequencies:
                        * 2412 MHz [1] (20.0 dBm)
                        * 2417 MHz [2] (20.0 dBm)
                        * 2422 MHz [3] (20.0 dBm)
                        * 2427 MHz [4] (20.0 dBm)
                        * 2432 MHz [5] (20.0 dBm)
                        * 2437 MHz [6] (20.0 dBm)
                        * 2442 MHz [7] (20.0 dBm)
                        * 2447 MHz [8] (20.0 dBm)
                        * 2452 MHz [9] (20.0 dBm)
                        * 2457 MHz [10] (20.0 dBm)
                        * 2462 MHz [11] (20.0 dBm)
                        * 2467 MHz [12] (disabled)
                        * 2472 MHz [13] (disabled)
                        * 2484 MHz [14] (disabled)
                Bitrates (non-HT):
                        * 1.0 Mbps
                        * 2.0 Mbps (short preamble supported)
                        * 5.5 Mbps (short preamble supported)
                        * 11.0 Mbps (short preamble supported)
                        * 6.0 Mbps
                        * 9.0 Mbps
                        * 12.0 Mbps
                        * 18.0 Mbps
                        * 24.0 Mbps
                        * 36.0 Mbps
                        * 48.0 Mbps
                        * 54.0 Mbps
        max # scan SSIDs: 4
        max scan IEs length: 2257 bytes
        Coverage class: 1 (up to 450m)
        Supported Ciphers:
                * WEP40 (00-0f-ac:1)
                * WEP104 (00-0f-ac:5)
                * TKIP (00-0f-ac:2)
                * CCMP (00-0f-ac:4)
                * CMAC (00-0f-ac:6)
        Available Antennas: TX 0x1 RX 0x1
        Configured Antennas: TX 0x1 RX 0x1
        Supported interface modes:
                 * IBSS
                 * managed
                 * AP
                 * AP/VLAN
                 * WDS
                 * monitor
                 * mesh point
                 * P2P-client
                 * P2P-GO
        software interface modes (can always be added):
                 * AP/VLAN
                 * monitor
        interface combinations are not supported
        Supported commands:
                 * new_interface
                 * set_interface
                 * new_key
                 * new_beacon
                 * new_station
                 * new_mpath
                 * set_mesh_params
                 * set_bss
                 * authenticate
                 * associate
                 * deauthenticate
                 * disassociate
                 * join_ibss
                 * join_mesh
                 * remain_on_channel
                 * set_tx_bitrate_mask
                 * action
                 * frame_wait_cancel
                 * set_wiphy_netns
                 * set_channel
                 * set_wds_peer
                 * Unknown command (82)
                 * Unknown command (81)
                 * Unknown command (84)
                 * Unknown command (87)
                 * Unknown command (85)
                 * connect
                 * disconnect
        Supported TX frame types:
                 * IBSS: 0x0000 0x0010 0x0020 0x0030 0x0040 0x0050 0x0060 0x0070 0x0080 0x0090 0x00a0 0x00b0 0x00c0 0x00d0 0x00e0 0x00f0
                 * managed: 0x0000 0x0010 0x0020 0x0030 0x0040 0x0050 0x0060 0x0070 0x0080 0x0090 0x00a0 0x00b0 0x00c0 0x00d0 0x00e0 0x00f0
                 * AP: 0x0000 0x0010 0x0020 0x0030 0x0040 0x0050 0x0060 0x0070 0x0080 0x0090 0x00a0 0x00b0 0x00c0 0x00d0 0x00e0 0x00f0
                 * AP/VLAN: 0x0000 0x0010 0x0020 0x0030 0x0040 0x0050 0x0060 0x0070 0x0080 0x0090 0x00a0 0x00b0 0x00c0 0x00d0 0x00e0 0x00f0
                 * mesh point: 0x0000 0x0010 0x0020 0x0030 0x0040 0x0050 0x0060 0x0070 0x0080 0x0090 0x00a0 0x00b0 0x00c0 0x00d0 0x00e0 0x00f0
                 * P2P-client: 0x0000 0x0010 0x0020 0x0030 0x0040 0x0050 0x0060 0x0070 0x0080 0x0090 0x00a0 0x00b0 0x00c0 0x00d0 0x00e0 0x00f0
                 * P2P-GO: 0x0000 0x0010 0x0020 0x0030 0x0040 0x0050 0x0060 0x0070 0x0080 0x0090 0x00a0 0x00b0 0x00c0 0x00d0 0x00e0 0x00f0
        Supported RX frame types:
                 * IBSS: 0x00d0
                 * managed: 0x0040 0x00d0
                 * AP: 0x0000 0x0020 0x0040 0x00a0 0x00b0 0x00c0 0x00d0
                 * AP/VLAN: 0x0000 0x0020 0x0040 0x00a0 0x00b0 0x00c0 0x00d0
                 * mesh point: 0x00b0 0x00c0 0x00d0
                 * P2P-client: 0x0040 0x00d0
                 * P2P-GO: 0x0000 0x0020 0x0040 0x00a0 0x00b0 0x00c0 0x00d0
        Device supports RSN-IBSS.
        HT Capability overrides:
                 * MCS: ff ff ff ff ff ff ff ff ff ff
                 * maximum A-MSDU length
                 * supported channel width
                 * short GI for 40 MHz
                 * max A-MPDU length exponent
                 * min MPDU start spacing
        Device supports HT-IBSS.
root@OpenWrt:~#

BTW, I need to mention that the same STA used to be able connect to openwrt with 80211n before, I can't remember the version but might before r2000.