hostapd AX Client Association Issue w/ 6GHz 320MHz AP

[Alex Gavin]

To Whom It May Concern:

When testing a mt7996-based 6GHz 320MHz AP on a custom 6.10.3+ kernel
and recent upstream hostapd (commit 70b8f64), AX clients will not associate.
However, BE clients will associate. Separately, all AX and BE clients will associate
when the AP is configured to 160MHz. In all cases, the clients are configured to
the 6GHz BSSID.

The following is a selection from the configuration file when configuring the AP
for 320MHz operation:

    ieee80211be=1
    channel=37
    op_class=137
    he_oper_centr_freq_seg0_idx=31
    eht_oper_centr_freq_seg0_idx=31
    he_6ghz_reg_pwr_type=0

With this configuration, the 'Channel Width' in the 'Control' field is set to
'0' (20 MHz). This is located in the '6GHz Operation Information' section of
the 'HE Operation' IE. Beacons from other 320MHz-configured APs (e.g. ASUS RT-BE96U,
Netgear RS700S) show the 'Channel Width' field set to '3' (160MHz or 80+80MHz).

Digging into the beacon creation code for this IE, 'center_idx_to_bw_6ghz()' returns '4'
for 320MHz operation. This overflows the two bit 'Channel Width' field, setting
'Channel Width' field to 0 (also setting the 'Duplicate Beacon' field to '1').

With the following hacked changes, I am able to associate AX clients again:

diff --git a/src/ap/ieee802_11_he.c b/src/ap/ieee802_11_he.c
index a2deda6c4..8b00abad1 100644
--- a/src/ap/ieee802_11_he.c
+++ b/src/ap/ieee802_11_he.c
@@ -252,7 +252,7 @@ u8 * hostapd_eid_he_operation(struct hostapd_data *hapd, u8 *eid)
                 *      bits 3-5: Regulatory Info
                 */
                /* Channel Width */
-               if (seg1)
+               if (seg1 || oper_chwidth == CONF_OPER_CHWIDTH_320MHZ)
                        control = 3;
                else
                        control = center_idx_to_bw_6ghz(seg0);

Can someone double check this partial configuration? I'm happy to provide the full config
if needed. If the config is correct, I am happy to submit this as a proper patch with any
needed modifications.

Best,
-- 
Alex Gavin
Candela Technologies, USA (PST/GMT-8)
Please CC support at candelatech.com on support topics.