ath5k: disable 5 GHz support for the dualband PHY chip on dual-radio AR5312

There are two variants of AR5312 dual-band devices, one single-radio
and the other one dual-radio. On the dual-radio board, the first MAC
only supports 5 GHz, even though it has a dual-band PHY. The 2.4 GHz
part of this phy is used in pass-through mode, connecting the second
MAC with the second PHY.
Disable 2.4 GHz for the first MAC on an AR5312, but only if the board
configuration indicates a dual-radio device.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath5k/ahb.c b/drivers/net/wireless/ath/ath5k/ahb.c
index 1374e64..ea99827 100644
--- a/drivers/net/wireless/ath/ath5k/ahb.c
+++ b/drivers/net/wireless/ath/ath5k/ahb.c
@@ -160,6 +160,16 @@
 		else
 			reg |= AR5K_AR5312_ENABLE_WLAN1;
 		__raw_writel(reg, (void __iomem *) AR5K_AR5312_ENABLE);
+
+		/*
+		 * On a dual-band AR5312, the multiband radio is only
+		 * used as pass-through. Disable 2 GHz support in the
+		 * driver for it
+		 */
+		if (to_platform_device(sc->dev)->id == 0 &&
+		    (bcfg->config->flags & (BD_WLAN0|BD_WLAN1)) ==
+		     (BD_WLAN1|BD_WLAN0))
+			__set_bit(ATH_STAT_2G_DISABLED, sc->status);
 	}
 
 	ret = ath5k_init_softc(sc, &ath_ahb_bus_ops);