ath5k: disable 32KHz sleep clock operation by default

While 32 KHz sleep clock might provide some power saving benefits,
it is also a major source of stability issues, on OpenWrt it produced
some reproducible data bus errors on register accesses on several
different MIPS platforms.

All the Atheros drivers that I can find do not enable this feature,
so it makes sense to leave it disabled in ath5k as well.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath5k/ath5k.h

@@ -1067,6 +1067,8 @@ struct ath5k_hw {
 	u8			ah_retry_long;
 	u8			ah_retry_short;
 
+	u32			ah_use_32khz_clock;
+
 	u8			ah_coverage_class;
 	bool			ah_ack_bitrate_high;
 	u8			ah_bwmode;

drivers/net/wireless/ath/ath5k/debug.c

@@ -922,6 +922,9 @@ ath5k_debug_init_device(struct ath5k_softc *sc)
 
 	debugfs_create_file("queue", S_IWUSR | S_IRUSR, phydir, sc,
 			    &fops_queue);
+
+	debugfs_create_bool("32khz_clock", S_IWUSR | S_IRUSR, phydir,
+			    &sc->ah->ah_use_32khz_clock);
 }
 
 /* functions used in other places */

drivers/net/wireless/ath/ath5k/reset.c

@@ -1287,11 +1287,16 @@ int ath5k_hw_reset(struct ath5k_hw *ah, enum nl80211_iftype op_mode,
 	ath5k_hw_dma_init(ah);
 
 
-	/* Enable 32KHz clock function for AR5212+ chips
+	/*
+	 * Enable 32KHz clock function for AR5212+ chips
 	 * Set clocks to 32KHz operation and use an
 	 * external 32KHz crystal when sleeping if one
-	 * exists */
-	if (ah->ah_version == AR5K_AR5212 &&
+	 * exists.
+	 * Disabled by default because it is also disabled in
+	 * other drivers and it is known to cause stability
+	 * issues on some devices
+	 */
+	if (ah->ah_use_32khz_clock && ah->ah_version == AR5K_AR5212 &&
 	    op_mode != NL80211_IFTYPE_AP)
 		ath5k_hw_set_sleep_clock(ah, true);