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Commit 7f896126 authored by Bruno Randolf's avatar Bruno Randolf Committed by John W. Linville
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ath5k: Check and fix ATIM window 

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: default avatarBruno Randolf <br1@einfach.org>
Signed-off-by: default avatarJohn W. Linville <linville@tuxdriver.com>
parent 4a79f2c5

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

+1 −0
Original line number Diff line number Diff line
@@ -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 */

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

+9 −0
Original line number Diff line number Diff line
@@ -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");

		}

	}

}

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

+91 −0
Original line number Diff line number Diff line
@@ -640,6 +640,97 @@ 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

 *