rt2x00: rt2800lib: fix VGC adjustment for RT3572 and RT3593

The Ralink DPO_RT5572_LinuxSTA_2.6.1.3_20121022
reference driver uses different RSSI threshold
and VGC adjustment values for the RT3572 and
RT3593 chipsets.

Update the rt2800_link_tuner function to use the
same values. Also change the comment in the function
to make it more generic.

References:

  RT35xx_ChipAGCAdjust function in chips/rt35xx.c
  RSSI_FOR_MID_LOW_SENSIBILITY constant in include/chip/rtmp_phy.h
  RT3593_R66_MID_LOW_SENS_GET macro in include/chip/rt3593.h
  RT3593_R66_NON_MID_LOW_SEMS_GET macro in include/chips/rt3593.h

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2800lib.c

@@ -4471,19 +4471,34 @@ void rt2800_link_tuner(struct rt2x00_dev *rt2x00dev, struct link_qual *qual,
 
 	if (rt2x00_rt_rev(rt2x00dev, RT2860, REV_RT2860C))
 		return;
-	/*
-	 * When RSSI is better then -80 increase VGC level with 0x10, except
-	 * for rt5592 chip.
+
+	/* When RSSI is better than a certain threshold, increase VGC
+	 * with a chip specific value in order to improve the balance
+	 * between sensibility and noise isolation.
 	 */
 
 	vgc = rt2800_get_default_vgc(rt2x00dev);
 
-	if (rt2x00_rt(rt2x00dev, RT5592)) {
+	switch (rt2x00dev->chip.rt) {
+	case RT3572:
+	case RT3593:
+		if (qual->rssi > -65) {
+			if (rt2x00dev->curr_band == IEEE80211_BAND_2GHZ)
+				vgc += 0x20;
+			else
+				vgc += 0x10;
+		}
+		break;
+
+	case RT5592:
 		if (qual->rssi > -65)
 			vgc += 0x20;
-	} else {
+		break;
+
+	default:
 		if (qual->rssi > -80)
 			vgc += 0x10;
+		break;
 	}
 
 	rt2800_set_vgc(rt2x00dev, qual, vgc);