From: Felix Fietkau <nbd@nbd.name>
Date: Wed, 25 Jan 2017 12:58:17 +0100
Subject: [PATCH] ath9k_hw: check if the chip failed to wake up

In an RFC patch, Sven Eckelmann and Simon Wunderlich reported:

"QCA 802.11n chips (especially AR9330/AR9340) sometimes end up in a
state in which a read of AR_CFG always returns 0xdeadbeef.
This should not happen when when the power_mode of the device is
ATH9K_PM_AWAKE."

Include the check for the default register state in the existing MAC
hang check.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
---

--- a/drivers/net/wireless/ath/ath9k/hw.c
+++ b/drivers/net/wireless/ath/ath9k/hw.c
@@ -1624,6 +1624,10 @@ bool ath9k_hw_check_alive(struct ath_hw
 	int count = 50;
 	u32 reg, last_val;
 
+	/* Check if chip failed to wake up */
+	if (REG_READ(ah, AR_CFG) == 0xdeadbeef)
+		return false;
+
 	if (AR_SREV_9300(ah))
 		return !ath9k_hw_detect_mac_hang(ah);