Enable setting the short-GI bit when TX'ing HT rates but only if the

hardware supports it.

Since ni->ni_htcap in hostap mode is what the remote end has advertised,
not what has been negotiated/decided, we need to check ourselves what
the current channel width is and what the hardware supports before
enabling short-GI.

It's important that short-GI isn't enabled when it isn't negotiated
and when the hardware doesn't support it (ie, short-gi for 20mhz channels
on any chip < AR9287.)

I've quickly verified this on the AR9285 in 11n mode.

1 files changed, 14 insertions, 6 deletions

diff --git a/sys/dev/ath/if_ath_tx_ht.c b/sys/dev/ath/if_ath_tx_ht.c
index f4ade31..348a1499 100644
--- a/sys/dev/ath/if_ath_tx_ht.c
+++ b/sys/dev/ath/if_ath_tx_ht.c
@@ -136,15 +136,23 @@ ath_rateseries_setup(struct ath_softc *sc, struct ieee80211_node *ni,
 	 	 */
 		if (ni->ni_chw == 40)
 			series[i].RateFlags |= HAL_RATESERIES_2040;
-#if 0
+
 		/*
-		 * The hardware only supports short-gi in 40mhz mode -
-		 * if later hardware supports it in 20mhz mode, be sure
-		 * to add the relevant check here.
+		 * Set short-GI only if the node has advertised it
+		 * the channel width is suitable, and we support it.
+		 * We don't currently have a "negotiated" set of bits -
+		 * ni_htcap is what the remote end sends, not what this
+		 * node is capable of.
 		 */
-		if (ni->ni_htcap & IEEE80211_HTCAP_SHORTGI40)
+		if (ni->ni_chw == 40 &&
+		    ic->ic_htcaps & IEEE80211_HTCAP_SHORTGI40 &&
+		    ni->ni_htcap & IEEE80211_HTCAP_SHORTGI40)
+			series[i].RateFlags |= HAL_RATESERIES_HALFGI;
+
+		if (ni->ni_chw == 20 &&
+		    ic->ic_htcaps & IEEE80211_HTCAP_SHORTGI20 &&
+		    ni->ni_htcap & IEEE80211_HTCAP_SHORTGI20)
 			series[i].RateFlags |= HAL_RATESERIES_HALFGI;
-#endif
 
 		series[i].Rate = rt->info[rix[i]].rateCode;