2 files changed, 44 insertions, 6 deletions

diff --git a/drivers/net/wireless/ath/ath5k/pcu.c b/drivers/net/wireless/ath/ath5k/pcu.c
index 174412fc81f8..5212e275f1c7 100644
--- a/drivers/net/wireless/ath/ath5k/pcu.c
+++ b/drivers/net/wireless/ath/ath5k/pcu.c
@@ -496,6 +496,8 @@ void ath5k_hw_set_rx_filter(struct ath5k_hw *ah, u32 filter)
 * Beacon control *
 \****************/
 
+#define ATH5K_MAX_TSF_READ 10
+
 /**
  * ath5k_hw_get_tsf64 - Get the full 64bit TSF
  *
@@ -505,10 +507,35 @@ void ath5k_hw_set_rx_filter(struct ath5k_hw *ah, u32 filter)
  */
 u64 ath5k_hw_get_tsf64(struct ath5k_hw *ah)
 {
-        u64 tsf = ath5k_hw_reg_read(ah, AR5K_TSF_U32);
+        u32 tsf_lower, tsf_upper1, tsf_upper2;
+        int i;
+
+        /*
+         * While reading TSF upper and then lower part, the clock is still
+         * counting (or jumping in case of IBSS merge) so we might get
+         * inconsistent values. To avoid this, we read the upper part again
+         * and check it has not been changed. We make the hypothesis that a
+         * maximum of 3 changes can happens in a row (we use 10 as a safe
+         * value).
+         *
+         * Impact on performance is pretty small, since in most cases, only
+         * 3 register reads are needed.
+         */
+
+        tsf_upper1 = ath5k_hw_reg_read(ah, AR5K_TSF_U32);
+        for (i = 0; i < ATH5K_MAX_TSF_READ; i++) {
+                tsf_lower = ath5k_hw_reg_read(ah, AR5K_TSF_L32);
+                tsf_upper2 = ath5k_hw_reg_read(ah, AR5K_TSF_U32);
+                if (tsf_upper2 == tsf_upper1)
+                        break;
+                tsf_upper1 = tsf_upper2;
+        }
+
+        WARN_ON( i == ATH5K_MAX_TSF_READ );
+
         ATH5K_TRACE(ah->ah_sc);
 
-        return ath5k_hw_reg_read(ah, AR5K_TSF_L32) | (tsf << 32);
+        return (((u64)tsf_upper1 << 32) | tsf_lower);
 }
 
 /**
diff --git a/drivers/net/wireless/ath/ath9k/hw.c b/drivers/net/wireless/ath/ath9k/hw.c
index 35f5cf40a990..894f5fc7489e 100644
--- a/drivers/net/wireless/ath/ath9k/hw.c
+++ b/drivers/net/wireless/ath/ath9k/hw.c
@@ -2420,14 +2420,25 @@ void ath9k_hw_write_associd(struct ath_hw *ah)
 }
 EXPORT_SYMBOL(ath9k_hw_write_associd);
 
+#define ATH9K_MAX_TSF_READ 10
+
 u64 ath9k_hw_gettsf64(struct ath_hw *ah)
 {
-        u64 tsf;
+        u32 tsf_lower, tsf_upper1, tsf_upper2;
+        int i;
+
+        tsf_upper1 = REG_READ(ah, AR_TSF_U32);
+        for (i = 0; i < ATH9K_MAX_TSF_READ; i++) {
+                tsf_lower = REG_READ(ah, AR_TSF_L32);
+                tsf_upper2 = REG_READ(ah, AR_TSF_U32);
+                if (tsf_upper2 == tsf_upper1)
+                        break;
+                tsf_upper1 = tsf_upper2;
+        }
 
-        tsf = REG_READ(ah, AR_TSF_U32);
-        tsf = (tsf << 32) | REG_READ(ah, AR_TSF_L32);
+        WARN_ON( i == ATH9K_MAX_TSF_READ );
 
-        return tsf;
+        return (((u64)tsf_upper1 << 32) | tsf_lower);
 }
 EXPORT_SYMBOL(ath9k_hw_gettsf64);