ath9k: differentiate quality reporting between legacy and HT configur…

…ations

We were not differentiating quality between legacy and HT
configurations. We change this to consider the differences.

New theory for reporting quality:

At a hardware RSSI of 45 you will be able to use MCS 7  reliably.
At a hardware RSSI of 45 you will be able to use MCS 15 reliably.
At a hardware RSSI of 35 you should be able use 54 Mbps reliably.

MCS 7  is the highets MCS index usable by a 1-stream device.
MCS 15 is the highest MCS index usable by a 2-stream device.

All ath9k devices are either 1-stream or 2-stream.

How many bars you see is derived from the qual reporting.

A more elaborate scheme can be used here but it requires tables
of SNR/throughput for each possible mode used. For the MCS table
you can refer to the wireless wiki:

http://wireless.kernel.org/en/developers/Documentation/ieee80211/802.11n

This should fix this bug report:

http://bugzilla.kernel.org/show_bug.cgi?id=13537

Cc: Janath.Peiris@atheros.com
Cc: Matt.Smith@atheros.com
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -236,10 +236,31 @@ static int ath_rx_prepare(struct sk_buff *skb, struct ath_desc *ds,
 	rx_status->signal = rx_status->noise + ds->ds_rxstat.rs_rssi;
 	rx_status->antenna = ds->ds_rxstat.rs_antenna;
 
-	/* at 45 you will be able to use MCS 15 reliably. A more elaborate
-	 * scheme can be used here but it requires tables of SNR/throughput for
-	 * each possible mode used. */
-	rx_status->qual =  ds->ds_rxstat.rs_rssi * 100 / 45;
+	/*
+	 * Theory for reporting quality:
+	 *
+	 * At a hardware RSSI of 45 you will be able to use MCS 7  reliably.
+	 * At a hardware RSSI of 45 you will be able to use MCS 15 reliably.
+	 * At a hardware RSSI of 35 you should be able use 54 Mbps reliably.
+	 *
+	 * MCS 7  is the highets MCS index usable by a 1-stream device.
+	 * MCS 15 is the highest MCS index usable by a 2-stream device.
+	 *
+	 * All ath9k devices are either 1-stream or 2-stream.
+	 *
+	 * How many bars you see is derived from the qual reporting.
+	 *
+	 * A more elaborate scheme can be used here but it requires tables
+	 * of SNR/throughput for each possible mode used. For the MCS table
+	 * you can refer to the wireless wiki:
+	 *
+	 * http://wireless.kernel.org/en/developers/Documentation/ieee80211/802.11n
+	 *
+	 */
+	if (conf_is_ht(&hw->conf))
+		rx_status->qual =  ds->ds_rxstat.rs_rssi * 100 / 45;
+	else
+		rx_status->qual =  ds->ds_rxstat.rs_rssi * 100 / 35;
 
 	/* rssi can be more than 45 though, anything above that
 	 * should be considered at 100% */