From 76355edba59fa964b52383ebc92c646c7057bee7 Mon Sep 17 00:00:00 2001
From: Adrian Chadd <adrian@FreeBSD.org>
Date: Sun, 29 May 2011 00:17:13 +0000
Subject: [PATCH] Teach if_ath about devices which have short-GI in 20MHz
 channel modes.

This has been disabled until now because there hasn't been any supported
device which has this feature. Since the AR9287 is the first device to
support it, and since now the HAL has functional AR9287+11n support,
flip this on.
---
 sys/dev/ath/ath_hal/ar9002/ar9287_attach.c |  5 +++++
 sys/dev/ath/if_ath.c                       | 17 +++++++++++++----
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/sys/dev/ath/ath_hal/ar9002/ar9287_attach.c b/sys/dev/ath/ath_hal/ar9002/ar9287_attach.c
index daee4148c49..fdf1f965e5f 100644
--- a/sys/dev/ath/ath_hal/ar9002/ar9287_attach.c
+++ b/sys/dev/ath/ath_hal/ar9002/ar9287_attach.c
@@ -439,9 +439,14 @@ ar9287FillCapabilityInfo(struct ath_hal *ah)
 	/* Disable this so Block-ACK works correctly */
 	pCap->halHasRxSelfLinkedTail = AH_FALSE;
 	pCap->halPSPollBroken = AH_FALSE;
+
+	/* Hardware supports (at least) single-stream STBC TX/RX */
 	pCap->halRxStbcSupport = 1;
 	pCap->halTxStbcSupport = 1;
 
+	/* Hardware supports short-GI w/ 20MHz */
+	pCap->halHTSGI20Support = 1;
+
 	return AH_TRUE;
 }
 
diff --git a/sys/dev/ath/if_ath.c b/sys/dev/ath/if_ath.c
index 745a0d5a950..552709872fc 100644
--- a/sys/dev/ath/if_ath.c
+++ b/sys/dev/ath/if_ath.c
@@ -627,13 +627,22 @@ ath_attach(u_int16_t devid, struct ath_softc *sc)
 			    | IEEE80211_HTC_AMPDU		/* A-MPDU tx/rx */
 			    | IEEE80211_HTC_AMSDU		/* A-MSDU tx/rx */
 			    | IEEE80211_HTCAP_MAXAMSDU_3839	/* max A-MSDU length */
-		/* At the present time, the hardware doesn't support short-GI in 20mhz mode */
-#if 0
-			    | IEEE80211_HTCAP_SHORTGI20		/* short GI in 20MHz */
-#endif
 			    | IEEE80211_HTCAP_SMPS_OFF;		/* SM power save off */
 			;
 
+		/*
+		 * Enable short-GI for HT20 only if the hardware
+		 * advertises support.
+		 * Notably, anything earlier than the AR9287 doesn't.
+		 */
+		if ((ath_hal_getcapability(ah,
+		    HAL_CAP_HT20_SGI, 0, NULL) == HAL_OK) &&
+		    (wmodes & HAL_MODE_HT20)) {
+			device_printf(sc->sc_dev,
+			    "[HT] enabling short-GI in 20MHz mode\n");
+			ic->ic_htcaps |= IEEE80211_HTCAP_SHORTGI20;
+		}
+
 		if (wmodes & HAL_MODE_HT40)
 			ic->ic_htcaps |= IEEE80211_HTCAP_CHWIDTH40
 			    |  IEEE80211_HTCAP_SHORTGI40;