ath9k_hw: Fix low throughput issue with AR93xx

TX underruns were noticed when RTS/CTS preceded aggregates.
This issue was noticed in ar93xx family of chipsets only.
The workaround involves padding the RTS or CTS length up
to the min packet length of 256 bytes required by the
hardware by adding delimiters to the fist descriptor of
the aggregate.
Signed-off-by: Senthil Balasubramanian <senthilkumar@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/ar9003_mac.c

@@ -410,12 +410,36 @@ static void ar9003_hw_set11n_ratescenario(struct ath_hw *ah, void *ds,
 static void ar9003_hw_set11n_aggr_first(struct ath_hw *ah, void *ds,
 					u32 aggrLen)
 {
+#define FIRST_DESC_NDELIMS 60
 	struct ar9003_txc *ads = (struct ar9003_txc *) ds;
 
 	ads->ctl12 |= (AR_IsAggr | AR_MoreAggr);
 
-	ads->ctl17 &= ~AR_AggrLen;
-	ads->ctl17 |= SM(aggrLen, AR_AggrLen);
+	if (ah->ent_mode & AR_ENT_OTP_MPSD) {
+		u32 ctl17, ndelim;
+		/*
+		 * Add delimiter when using RTS/CTS with aggregation
+		 * and non enterprise AR9003 card
+		 */
+		ctl17 = ads->ctl17;
+		ndelim = MS(ctl17, AR_PadDelim);
+
+		if (ndelim < FIRST_DESC_NDELIMS) {
+			aggrLen += (FIRST_DESC_NDELIMS - ndelim) * 4;
+			ndelim = FIRST_DESC_NDELIMS;
+		}
+
+		ctl17 &= ~AR_AggrLen;
+		ctl17 |= SM(aggrLen, AR_AggrLen);
+
+		ctl17 &= ~AR_PadDelim;
+		ctl17 |= SM(ndelim, AR_PadDelim);
+
+		ads->ctl17 = ctl17;
+	} else {
+		ads->ctl17 &= ~AR_AggrLen;
+		ads->ctl17 |= SM(aggrLen, AR_AggrLen);
+	}
 }
 
 static void ar9003_hw_set11n_aggr_middle(struct ath_hw *ah, void *ds,

drivers/net/wireless/ath/ath9k/hw.c

@@ -1952,6 +1952,9 @@ int ath9k_hw_fill_cap_info(struct ath_hw *ah)
 	if (AR_SREV_9300_20_OR_LATER(ah))
 		pCap->hw_caps |= ATH9K_HW_CAP_RAC_SUPPORTED;
 
+	if (AR_SREV_9300_20_OR_LATER(ah))
+		ah->ent_mode = REG_READ(ah, AR_ENT_OTP);
+
 	if (AR_SREV_9287_11_OR_LATER(ah) || AR_SREV_9271(ah))
 		pCap->hw_caps |= ATH9K_HW_CAP_SGI_20;
 

drivers/net/wireless/ath/ath9k/hw.h

@@ -803,6 +803,9 @@ struct ath_hw {
 	 * this register when in sleep states.
 	 */
 	u32 WARegVal;
+
+	/* Enterprise mode cap */
+	u32 ent_mode;
 };
 
 static inline struct ath_common *ath9k_hw_common(struct ath_hw *ah)

drivers/net/wireless/ath/ath9k/reg.h

@@ -1067,6 +1067,7 @@ enum {
 #define AR_INTR_PRIO_ASYNC_ENABLE 0x40d4
 #define AR_ENT_OTP		  0x40d8
 #define AR_ENT_OTP_CHAIN2_DISABLE               0x00020000
+#define AR_ENT_OTP_MPSD		0x00800000
 
 #define AR_RTC_9300_PLL_DIV          0x000003ff
 #define AR_RTC_9300_PLL_DIV_S        0