ar9170: handle otus' A-MPDU density definitions

Otus uses slightly different set of "Minimum MPDU Start Spacing" values
than the 802.11n D2.0 specifies. (the whole table is shifted by one and
therefore the 16us spacing is not officially available!)

And while we're at it, we also initialize our MAC's density register.
So, this annoying _feature_ will not break TX A-MPDU later.
Signed-off-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ar9170/hw.h

@@ -207,6 +207,8 @@ enum ar9170_cmd {
 #define AR9170_MAC_REG_AC1_AC0_TXOP		(AR9170_MAC_REG_BASE + 0xB44)
 #define AR9170_MAC_REG_AC3_AC2_TXOP		(AR9170_MAC_REG_BASE + 0xB48)
 
+#define AR9170_MAC_REG_AMPDU_SET		(AR9170_MAC_REG_BASE + 0xba0)
+
 #define AR9170_MAC_REG_ACK_TABLE		(AR9170_MAC_REG_BASE + 0xC00)
 #define AR9170_MAC_REG_AMPDU_RX_THRESH		(AR9170_MAC_REG_BASE + 0xC50)
 

drivers/net/wireless/ath/ar9170/mac.c

@@ -72,6 +72,24 @@ int ar9170_set_qos(struct ar9170 *ar)
 	return ar9170_regwrite_result();
 }
 
+static int ar9170_set_ampdu_density(struct ar9170 *ar, u8 mpdudensity)
+{
+	u32 val;
+
+	/* don't allow AMPDU density > 8us */
+	if (mpdudensity > 6)
+		return -EINVAL;
+
+	/* Watch out! Otus uses slightly different density values. */
+	val = 0x140a00 | (mpdudensity ? (mpdudensity + 1) : 0);
+
+	ar9170_regwrite_begin(ar);
+	ar9170_regwrite(AR9170_MAC_REG_AMPDU_SET, val);
+	ar9170_regwrite_finish();
+
+	return ar9170_regwrite_result();
+}
+
 int ar9170_init_mac(struct ar9170 *ar)
 {
 	ar9170_regwrite_begin(ar);
@@ -296,6 +314,11 @@ int ar9170_set_operating_mode(struct ar9170 *ar)
 	if (err)
 		return err;
 
+	/* set AMPDU density to 8us. */
+	err = ar9170_set_ampdu_density(ar, 6);
+	if (err)
+		return err;
+
 	ar9170_regwrite_begin(ar);
 
 	ar9170_regwrite(AR9170_MAC_REG_POWERMANAGEMENT, pm_mode);

drivers/net/wireless/ath/ar9170/main.c

@@ -151,8 +151,8 @@ static struct ieee80211_channel ar9170_5ghz_chantable[] = {
 			  IEEE80211_HT_CAP_SGI_40 |			\
 			  IEEE80211_HT_CAP_DSSSCCK40 |			\
 			  IEEE80211_HT_CAP_SM_PS,			\
-	.ampdu_factor	= 3, /* ?? */					\
-	.ampdu_density	= 7, /* ?? */					\
+	.ampdu_factor	= 3,						\
+	.ampdu_density	= 6,						\
 	.mcs		= {						\
 		.rx_mask = { 0xFF, 0xFF, 0, 0, 0, 0, 0, 0, 0, 0, },	\
 	},								\