ath9k: fix TSF after reset on AR913x

When issuing a reset, the TSF value is lost in the hardware because of
the 913x specific cold reset. As with some AR9280 cards, the TSF needs
to be preserved in software here.

Additionally, there's an issue that frequently prevents a successful
TSF write directly after the chip reset. In this case, repeating the
TSF write after the initval-writes usually works.

This patch detects failed TSF writes and recovers from them, taking
into account the delay caused by the initval writes.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Reported-by: Björn Smedman <bjorn.smedman@venatech.se>
Cc: stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>

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

@@ -1268,7 +1268,8 @@ int ath9k_hw_reset(struct ath_hw *ah, struct ath9k_channel *chan,
 	macStaId1 = REG_READ(ah, AR_STA_ID1) & AR_STA_ID1_BASE_RATE_11B;
 
 	/* For chips on which RTC reset is done, save TSF before it gets cleared */
-	if (AR_SREV_9280(ah) && ah->eep_ops->get_eeprom(ah, EEP_OL_PWRCTRL))
+	if (AR_SREV_9100(ah) ||
+	    (AR_SREV_9280(ah) && ah->eep_ops->get_eeprom(ah, EEP_OL_PWRCTRL)))
 		tsf = ath9k_hw_gettsf64(ah);
 
 	saveLedState = REG_READ(ah, AR_CFG_LED) &
@@ -1300,7 +1301,7 @@ int ath9k_hw_reset(struct ath_hw *ah, struct ath9k_channel *chan,
 	}
 
 	/* Restore TSF */
-	if (tsf && AR_SREV_9280(ah) && ah->eep_ops->get_eeprom(ah, EEP_OL_PWRCTRL))
+	if (tsf)
 		ath9k_hw_settsf64(ah, tsf);
 
 	if (AR_SREV_9280_10_OR_LATER(ah))
@@ -1313,6 +1314,17 @@ int ath9k_hw_reset(struct ath_hw *ah, struct ath9k_channel *chan,
 	if (r)
 		return r;
 
+	/*
+	 * Some AR91xx SoC devices frequently fail to accept TSF writes
+	 * right after the chip reset. When that happens, write a new
+	 * value after the initvals have been applied, with an offset
+	 * based on measured time difference
+	 */
+	if (AR_SREV_9100(ah) && (ath9k_hw_gettsf64(ah) < tsf)) {
+		tsf += 1500;
+		ath9k_hw_settsf64(ah, tsf);
+	}
+
 	/* Setup MFP options for CCMP */
 	if (AR_SREV_9280_20_OR_LATER(ah)) {
 		/* Mask Retry(b11), PwrMgt(b12), MoreData(b13) to 0 in mgmt