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.

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 daee414..fdf1f96 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 745a0d5..5527098 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;