[PATCH v2] ath9k: mark RSSI as invalid if frame received during channel setup

[Jean Pierre TOSONI]

ath9k returns a wrong RSSI value for frames received in a 30ms time
window after a channel change. The correct value is typically 10dB
below the returned value.

This was found with a Atheros AR9300 Rev:3 chip (WLE350NX / JWX6083
cards), during offchannel scans.

Mark the signal value as invalid in this case.

Signed-off-by: Jean Pierre TOSONI <jp.tos...@acksys.fr>
---
V2: replace LEDE patch with due kernel patch (with excuses to Kalle Valo)

 drivers/net/wireless/ath/ath9k/ani.c    |    1 +
 drivers/net/wireless/ath/ath9k/common.c |   10 ++++++++++
 drivers/net/wireless/ath/ath9k/hw.h     |    1 +
 3 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/drivers/net/wireless/ath/ath9k/ani.c 
b/drivers/net/wireless/ath/ath9k/ani.c
index 5214dd7..a7e07ed 100644
--- a/drivers/net/wireless/ath/ath9k/ani.c
+++ b/drivers/net/wireless/ath/ath9k/ani.c
@@ -317,6 +317,7 @@ void ath9k_ani_reset(struct ath_hw *ah, bool is_scanning)
                return;
 
        BUG_ON(aniState == NULL);
+       ah->chan_stable_time = jiffies + (30*HZ)/1000; /* 30ms */
        ah->stats.ast_ani_reset++;
 
        ofdm_nil = max_t(int, ATH9K_ANI_OFDM_DEF_LEVEL,
diff --git a/drivers/net/wireless/ath/ath9k/common.c 
b/drivers/net/wireless/ath/ath9k/common.c
index 099f3d4..7e5f7a3 100644
--- a/drivers/net/wireless/ath/ath9k/common.c
+++ b/drivers/net/wireless/ath/ath9k/common.c
@@ -221,6 +221,16 @@ void ath9k_cmn_process_rssi(struct ath_common *common,
        int i, j;
 
        /*
+        * RSSI is not available before 30ms after reset on ath9k.
+        */
+       if (time_before(jiffies, ah->chan_stable_time)) {
+               ath_dbg(common, ANY, "early frame rssi=%d\n",rx_stats->rs_rssi);
+               rxs->flag |= RX_FLAG_NO_SIGNAL_VAL;
+               return;
+       }
+       ah->chan_stable_time = jiffies; /* advance stable time to cop with 
jiffies wraparound */
+
+       /*
         * RSSI is not available for subframes in an A-MPDU.
         */
        if (rx_stats->rs_moreaggr) {
diff --git a/drivers/net/wireless/ath/ath9k/hw.h 
b/drivers/net/wireless/ath/ath9k/hw.h
index 9804a24..ec07da9 100644
--- a/drivers/net/wireless/ath/ath9k/hw.h
+++ b/drivers/net/wireless/ath/ath9k/hw.h
@@ -809,6 +809,7 @@ struct ath_hw {
 
        bool reset_power_on;
        bool htc_reset_init;
+       unsigned long chan_stable_time;
 
        enum nl80211_iftype opmode;
        enum ath9k_power_mode power_mode;
-- 
1.7.2.5