This patch adds sanity-checks for the beacon timers and especially the ATIM window to ath5k. It is basically the same what i did for madwifi two years ago and fixes a problem in IBSS mode which has been described as "ramping" pings. See the code comments for a more detailed description and these links: http://madwifi-project.org/ticket/1154 http://madwifi-project.org/changeset/3867 http://thread.gmane.org/gmane.linux.drivers.madwifi.devel/6066 Signed-off-by: Bruno Randolf <br1@xxxxxxxxxxx> --- drivers/net/wireless/ath/ath5k/ath5k.h | 1 drivers/net/wireless/ath/ath5k/base.c | 9 +++ drivers/net/wireless/ath/ath5k/pcu.c | 91 ++++++++++++++++++++++++++++++++ 3 files changed, 101 insertions(+), 0 deletions(-) diff --git a/drivers/net/wireless/ath/ath5k/ath5k.h b/drivers/net/wireless/ath/ath5k/ath5k.h index 42e6e82..0cba2e3 100644 --- a/drivers/net/wireless/ath/ath5k/ath5k.h +++ b/drivers/net/wireless/ath/ath5k/ath5k.h @@ -1195,6 +1195,7 @@ u64 ath5k_hw_get_tsf64(struct ath5k_hw *ah); void ath5k_hw_set_tsf64(struct ath5k_hw *ah, u64 tsf64); void ath5k_hw_reset_tsf(struct ath5k_hw *ah); void ath5k_hw_init_beacon(struct ath5k_hw *ah, u32 next_beacon, u32 interval); +bool ath5k_hw_check_beacon_timers(struct ath5k_hw *ah, int intval); /* ACK bit rate */ void ath5k_hw_set_ack_bitrate_high(struct ath5k_hw *ah, bool high); /* Clock rate related functions */ diff --git a/drivers/net/wireless/ath/ath5k/base.c b/drivers/net/wireless/ath/ath5k/base.c index 95072db..4103765 100644 --- a/drivers/net/wireless/ath/ath5k/base.c +++ b/drivers/net/wireless/ath/ath5k/base.c @@ -1191,6 +1191,15 @@ ath5k_check_ibss_tsf(struct ath5k_softc *sc, struct sk_buff *skb, */ if (hw_tu >= sc->nexttbtt) ath5k_beacon_update_timers(sc, bc_tstamp); + + /* Check if the beacon timers are still correct, because a TSF + * update might have created a window between them - for a + * longer description see the comment of this function: */ + if (!ath5k_hw_check_beacon_timers(sc->ah, sc->bintval)) { + ath5k_beacon_update_timers(sc, bc_tstamp); + ATH5K_DBG_UNLIMIT(sc, ATH5K_DEBUG_BEACON, + "fixed beacon timers after beacon receive\n"); + } } } diff --git a/drivers/net/wireless/ath/ath5k/pcu.c b/drivers/net/wireless/ath/ath5k/pcu.c index 71dca10..604114f 100644 --- a/drivers/net/wireless/ath/ath5k/pcu.c +++ b/drivers/net/wireless/ath/ath5k/pcu.c @@ -641,6 +641,97 @@ void ath5k_hw_init_beacon(struct ath5k_hw *ah, u32 next_beacon, u32 interval) } /** + * ath5k_check_timer_win - Check if timer B is timer A + window + * + * @a: timer a (before b) + * @b: timer b (after a) + * @window: difference between a and b + * @intval: timers are increased by this interval + * + * This helper function checks if timer B is timer A + window and covers + * cases where timer A or B might have already been updated or wrapped + * around (Timers are 16 bit). + * + * Returns true if O.K. + */ +static inline bool +ath5k_check_timer_win(int a, int b, int window, int intval) +{ + /* + * 1.) usually B should be A + window + * 2.) A already updated, B not updated yet + * 3.) A already updated and has wrapped around + * 4.) B has wrapped around + */ + if ((b - a == window) || /* 1.) */ + (a - b == intval - window) || /* 2.) */ + ((a | 0x10000) - b == intval - window) || /* 3.) */ + ((b | 0x10000) - a == window)) /* 4.) */ + return true; /* O.K. */ + return false; +} + +/** + * ath5k_hw_check_beacon_timers - Check if the beacon timers are correct + * + * @ah: The &struct ath5k_hw + * @intval: beacon interval + * + * This is a workaround for IBSS mode: + * + * The need for this function arises from the fact that we have 4 separate + * HW timer registers (TIMER0 - TIMER3), which are closely related to the + * next beacon target time (NBTT), and that the HW updates these timers + * seperately based on the current TSF value. The hardware increments each + * timer by the beacon interval, when the local TSF coverted to TU is equal + * to the value stored in the timer. + * + * The reception of a beacon with the same BSSID can update the local HW TSF + * at any time - this is something we can't avoid. If the TSF jumps to a + * time which is later than the time stored in a timer, this timer will not + * be updated until the TSF in TU wraps around at 16 bit (the size of the + * timers) and reaches the time which is stored in the timer. + * + * The problem is that these timers are closely related to TIMER0 (NBTT) and + * that they define a time "window". When the TSF jumps between two timers + * (e.g. ATIM and NBTT), the one in the past will be left behind (not + * updated), while the one in the future will be updated every beacon + * interval. This causes the window to get larger, until the TSF wraps + * around as described above and the timer which was left behind gets + * updated again. But - because the beacon interval is usually not an exact + * divisor of the size of the timers (16 bit), an unwanted "window" between + * these timers has developed! + * + * This is especially important with the ATIM window, because during + * the ATIM window only ATIM frames and no data frames are allowed to be + * sent, which creates transmission pauses after each beacon. This symptom + * has been described as "ramping ping" because ping times increase linearly + * for some time and then drop down again. A wrong window on the DMA beacon + * timer has the same effect, so we check for these two conditions. + * + * Returns true if O.K. + */ +bool +ath5k_hw_check_beacon_timers(struct ath5k_hw *ah, int intval) +{ + unsigned int nbtt, atim, dma; + + nbtt = ath5k_hw_reg_read(ah, AR5K_TIMER0); + atim = ath5k_hw_reg_read(ah, AR5K_TIMER3); + dma = ath5k_hw_reg_read(ah, AR5K_TIMER1) >> 3; + + /* NOTE: SWBA is different. Having a wrong window there does not + * stop us from sending data and this condition is catched thru + * other means (SWBA interrupt) */ + + if (ath5k_check_timer_win(nbtt, atim, 1, intval) && + ath5k_check_timer_win(dma, nbtt, AR5K_TUNE_DMA_BEACON_RESP, + intval)) + return true; /* O.K. */ + return false; +} + +/** * ath5k_hw_set_coverage_class - Set IEEE 802.11 coverage class * * @ah: The &struct ath5k_hw -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
