mac80211: enable TDLS peer buffer STA feature

Allow drivers to set the buffer station extended capability
for TDLS links, with a new hardware flag indicating this.

Signed-off-by: Yingying Tang <[e-mail]>
[change commit log/documentation wording]
Signed-off-by: Johannes Berg <[e-mail]>

include/net/mac80211.h

···
  *	The stack will not do fragmentation.
  *	The callback for @set_frag_threshold should be set as well.
  *
+ * @IEEE80211_HW_SUPPORTS_TDLS_BUFFER_STA: Hardware supports buffer STA on
+ *	TDLS links.
+ *
  * @NUM_IEEE80211_HW_FLAGS: number of hardware flags, used for sizing arrays
  */
 enum ieee80211_hw_flags {
···
 	IEEE80211_HW_TX_FRAG_LIST,
 	IEEE80211_HW_REPORTS_LOW_ACK,
 	IEEE80211_HW_SUPPORTS_TX_FRAG,
+	IEEE80211_HW_SUPPORTS_TDLS_BUFFER_STA,
 
 	/* keep last, obviously */
 	NUM_IEEE80211_HW_FLAGS

net/mac80211/debugfs.c

···
 	FLAG(TX_FRAG_LIST),
 	FLAG(REPORTS_LOW_ACK),
 	FLAG(SUPPORTS_TX_FRAG),
+	FLAG(SUPPORTS_TDLS_BUFFER_STA),
 #undef FLAG
 };
 

net/mac80211/tdls.c

···
 			   NL80211_FEATURE_TDLS_CHANNEL_SWITCH;
 	bool wider_band = ieee80211_hw_check(&local->hw, TDLS_WIDER_BW) &&
 			  !ifmgd->tdls_wider_bw_prohibited;
+	bool buffer_sta = ieee80211_hw_check(&local->hw,
+					     SUPPORTS_TDLS_BUFFER_STA);
 	struct ieee80211_supported_band *sband = ieee80211_get_sband(sdata);
 	bool vht = sband && sband->vht_cap.vht_supported;
 	u8 *pos = skb_put(skb, 10);
···
 	*pos++ = 0x0;
 	*pos++ = 0x0;
 	*pos++ = 0x0;
-	*pos++ = chan_switch ? WLAN_EXT_CAPA4_TDLS_CHAN_SWITCH : 0;
+	*pos++ = (chan_switch ? WLAN_EXT_CAPA4_TDLS_CHAN_SWITCH : 0) |
+		 (buffer_sta ? WLAN_EXT_CAPA4_TDLS_BUFFER_STA : 0);
 	*pos++ = WLAN_EXT_CAPA5_TDLS_ENABLED;
 	*pos++ = 0;
 	*pos++ = 0;