src/net/80211/rc80211.c - ipxe - Git at Google

 /*
  * Simple 802.11 rate-control algorithm for iPXE.
  *
  * Copyright (c) 2009 Joshua Oreman <oremanj@rwcr.net>.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
  * published by the Free Software Foundation; either version 2 of the
  * License, or any later version.
  *
  * This program is distributed in the hope that it will be useful, but
  * WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  * 02110-1301, USA.
  */

 FILE_LICENCE ( GPL2_OR_LATER );

 #include <stdlib.h>
 #include <ipxe/net80211.h>

 /**
  * @file
  *
  * Simple 802.11 rate-control algorithm
  */

 /** @page rc80211 Rate control philosophy
  *
  * We want to maximize our transmission speed, to the extent that we
  * can do that without dropping undue numbers of packets. We also
  * don't want to take up very much code space, so our algorithm has to
  * be pretty simple
  *
  * When we receive a packet, we know what rate it was transmitted at,
  * and whether it had to be retransmitted to get to us.
  *
  * When we send a packet, we hear back how many times it had to be
  * retried to get through, and whether it got through at all.
  *
  * Indications of TX success are more reliable than RX success, but RX
  * information helps us know where to start.
  *
  * To handle all of this, we keep for each rate and each direction (TX
  * and RX separately) some state information for the most recent
  * packets on that rate and the number of packets for which we have
  * information. The state is a 32-bit unsigned integer in which two
  * bits represent a packet: 11 if it went through well, 10 if it went
  * through with one retry, 01 if it went through with more than one
  * retry, or 00 if it didn't go through at all. We define the
  * "goodness" for a particular (rate, direction) combination as the
  * sum of all the 2-bit fields, times 33, divided by the number of
  * 2-bit fields containing valid information (16 except when we're
  * starting out). The number produced is between 0 and 99; we use -1
  * for rates with less than 4 RX packets or 1 TX, as an indicator that
  * we do not have enough information to rely on them.
  *
  * In deciding which rates are best, we find the weighted average of
  * TX and RX goodness, where the weighting is by number of packets
  * with data and TX packets are worth 4 times as much as RX packets.
  * The weighted average is called "net goodness" and is also a number
  * between 0 and 99.  If 3 consecutive packets fail transmission
  * outright, we automatically ratchet down the rate; otherwise, we
  * switch to the best rate whenever the current rate's goodness falls
  * below some threshold, and try increasing our rate when the goodness
  * is very high.
  *
  * This system is optimized for iPXE's style of usage. Because normal
  * operation always involves receiving something, we'll make our way
  * to the best rate pretty quickly. We tend to follow the lead of the
  * sending AP in choosing rates, but we won't use rates for long that
  * don't work well for us in transmission. We assume iPXE won't be
  * running for long enough that rate patterns will change much, so we
  * don't have to keep time counters or the like.  And if this doesn't
  * work well in practice there are many ways it could be tweaked.
  *
  * To avoid staying at 1Mbps for a long time, we don't track any
  * transmitted packets until we've set our rate based on received
  * packets.
  */

 /** Two-bit packet status indicator for a packet with no retries */
 #define RC_PKT_OK		0x3

 /** Two-bit packet status indicator for a packet with one retry */
 #define RC_PKT_RETRIED_ONCE	0x2

 /** Two-bit packet status indicator for a TX packet with multiple retries
  *
  * It is not possible to tell whether an RX packet had one or multiple
  * retries; we rely instead on the fact that failed RX packets won't
  * get to us at all, so if we receive a lot of RX packets on a certain
  * rate it must be pretty good.
  */
 #define RC_PKT_RETRIED_MULTI	0x1

 /** Two-bit packet status indicator for a TX packet that was never ACKed
  *
  * It is not possible to tell whether an RX packet was setn if it
  * didn't get through to us, but if we don't see one we won't increase
  * the goodness for its rate. This asymmetry is part of why TX packets
  * are weighted much more heavily than RX.
  */
 #define RC_PKT_FAILED		0x0

 /** Number of times to weight TX packets more heavily than RX packets */
 #define RC_TX_FACTOR		4

 /** Number of consecutive failed TX packets that cause an automatic rate drop */
 #define RC_TX_EMERG_FAIL	3

 /** Minimum net goodness below which we will search for a better rate */
 #define RC_GOODNESS_MIN		85

 /** Maximum net goodness above which we will try to increase our rate */
 #define RC_GOODNESS_MAX		95

 /** Minimum (num RX + @c RC_TX_FACTOR * num TX) to use a certain rate */
 #define RC_UNCERTAINTY_THRESH	4

 /** TX direction */
 #define TX	0

 /** RX direction */
 #define RX	1

 /** A rate control context */
 struct rc80211_ctx
 {
 	/** Goodness state for each rate, TX and RX */
 	u32 goodness[2][NET80211_MAX_RATES];

 	/** Number of packets recorded for each rate */
 	u8 count[2][NET80211_MAX_RATES];

 	/** Indication of whether we've set the device rate yet */
 	int started;

 	/** Counter of all packets sent and received */
 	int packets;
 };

 /**
  * Initialize rate-control algorithm
  *
  * @v dev	802.11 device
  * @ret ctx	Rate-control context, to be stored in @c dev->rctl
  */
 struct rc80211_ctx * rc80211_init ( struct net80211_device *dev __unused )
 {
 	struct rc80211_ctx *ret = zalloc ( sizeof ( *ret ) );
 	return ret;
 }

 /**
  * Calculate net goodness for a certain rate
  *
  * @v ctx	Rate-control context
  * @v rate_idx	Index of rate to calculate net goodness for
  */
 static int rc80211_calc_net_goodness ( struct rc80211_ctx *ctx,
 				       int rate_idx )
 {
 	int sum[2], num[2], dir, pkt;

 	for ( dir = 0; dir < 2; dir++ ) {
 		u32 good = ctx->goodness[dir][rate_idx];

 		num[dir] = ctx->count[dir][rate_idx];
 		sum[dir] = 0;

 		for ( pkt = 0; pkt < num[dir]; pkt++ )
 			sum[dir] += ( good >> ( 2 * pkt ) ) & 0x3;
 	}

 	if ( ( num[TX] * RC_TX_FACTOR + num[RX] ) < RC_UNCERTAINTY_THRESH )
 		return -1;

 	return ( 33 * ( sum[TX] * RC_TX_FACTOR + sum[RX] ) /
 		      ( num[TX] * RC_TX_FACTOR + num[RX] ) );
 }

 /**
  * Determine the best rate to switch to and return it
  *
  * @v dev		802.11 device
  * @ret rate_idx	Index of the best rate to switch to
  */
 static int rc80211_pick_best ( struct net80211_device *dev )
 {
 	struct rc80211_ctx *ctx = dev->rctl;
 	int best_net_good = 0, best_rate = -1, i;

 	for ( i = 0; i < dev->nr_rates; i++ ) {
 		int net_good = rc80211_calc_net_goodness ( ctx, i );

 		if ( net_good > best_net_good ||
 		     ( best_net_good > RC_GOODNESS_MIN &&
 		       net_good > RC_GOODNESS_MIN ) ) {
 			best_net_good = net_good;
 			best_rate = i;
 		}
 	}

 	if ( best_rate >= 0 ) {
 		int old_good = rc80211_calc_net_goodness ( ctx, dev->rate );
 		if ( old_good != best_net_good )
 			DBGC ( ctx, "802.11 RC %p switching from goodness "
 			       "%d to %d\n", ctx, old_good, best_net_good );

 		ctx->started = 1;
 		return best_rate;
 	}

 	return dev->rate;
 }

 /**
  * Set 802.11 device rate
  *
  * @v dev	802.11 device
  * @v rate_idx	Index of rate to switch to
  *
  * This is a thin wrapper around net80211_set_rate_idx to insert a
  * debugging message where appropriate.
  */
 static inline void rc80211_set_rate ( struct net80211_device *dev,
 				      int rate_idx )
 {
 	DBGC ( dev->rctl, "802.11 RC %p changing rate %d->%d Mbps\n", dev->rctl,
 	       dev->rates[dev->rate] / 10, dev->rates[rate_idx] / 10 );

 	net80211_set_rate_idx ( dev, rate_idx );
 }

 /**
  * Check rate-control state and change rate if necessary
  *
  * @v dev	802.11 device
  */
 static void rc80211_maybe_set_new ( struct net80211_device *dev )
 {
 	struct rc80211_ctx *ctx = dev->rctl;
 	int net_good;

 	net_good = rc80211_calc_net_goodness ( ctx, dev->rate );

 	if ( ! ctx->started ) {
 		rc80211_set_rate ( dev, rc80211_pick_best ( dev ) );
 		return;
 	}

 	if ( net_good < 0 )	/* insufficient data */
 		return;

 	if ( net_good > RC_GOODNESS_MAX && dev->rate + 1 < dev->nr_rates ) {
 		int higher = rc80211_calc_net_goodness ( ctx, dev->rate + 1 );
 		if ( higher > net_good || higher < 0 )
 			rc80211_set_rate ( dev, dev->rate + 1 );
 		else
 			rc80211_set_rate ( dev, rc80211_pick_best ( dev ) );
 	}

 	if ( net_good < RC_GOODNESS_MIN ) {
 		rc80211_set_rate ( dev, rc80211_pick_best ( dev ) );
 	}
 }

 /**
  * Update rate-control state
  *
  * @v dev		802.11 device
  * @v direction		One of the direction constants TX or RX
  * @v rate_idx		Index of rate at which packet was sent or received
  * @v retries		Number of times packet was retried before success
  * @v failed		If nonzero, the packet failed to get through
  */
 static void rc80211_update ( struct net80211_device *dev, int direction,
 			     int rate_idx, int retries, int failed )
 {
 	struct rc80211_ctx *ctx = dev->rctl;
 	u32 goodness = ctx->goodness[direction][rate_idx];

 	if ( ctx->count[direction][rate_idx] < 16 )
 		ctx->count[direction][rate_idx]++;

 	goodness <<= 2;
 	if ( failed )
 		goodness |= RC_PKT_FAILED;
 	else if ( retries > 1 )
 		goodness |= RC_PKT_RETRIED_MULTI;
 	else if ( retries )
 		goodness |= RC_PKT_RETRIED_ONCE;
 	else
 		goodness |= RC_PKT_OK;

 	ctx->goodness[direction][rate_idx] = goodness;

 	ctx->packets++;

 	rc80211_maybe_set_new ( dev );
 }

 /**
  * Update rate-control state for transmitted packet
  *
  * @v dev	802.11 device
  * @v retries	Number of times packet was transmitted before success
  * @v rc	Return status code for transmission
  */
 void rc80211_update_tx ( struct net80211_device *dev, int retries, int rc )
 {
 	struct rc80211_ctx *ctx = dev->rctl;

 	if ( ! ctx->started )
 		return;

 	rc80211_update ( dev, TX, dev->rate, retries, rc );

 	/* Check if the last RC_TX_EMERG_FAIL packets have all failed */
 	if ( ! ( ctx->goodness[TX][dev->rate] &
 		 ( ( 1 << ( 2 * RC_TX_EMERG_FAIL ) ) - 1 ) ) ) {
 		if ( dev->rate == 0 )
 			DBGC ( dev->rctl, "802.11 RC %p saw %d consecutive "
 			       "failed TX, but cannot lower rate any further\n",
 			       dev->rctl, RC_TX_EMERG_FAIL );
 		else {
 			DBGC ( dev->rctl, "802.11 RC %p lowering rate (%d->%d "
 			       "Mbps) due to %d consecutive TX failures\n",
 			       dev->rctl, dev->rates[dev->rate] / 10,
 			       dev->rates[dev->rate - 1] / 10,
 			       RC_TX_EMERG_FAIL );

 			rc80211_set_rate ( dev, dev->rate - 1 );
 		}
 	}
 }

 /**
  * Update rate-control state for received packet
  *
  * @v dev	802.11 device
  * @v retry	Whether the received packet had been retransmitted
  * @v rate	Rate at which packet was received, in 100 kbps units
  */
 void rc80211_update_rx ( struct net80211_device *dev, int retry, u16 rate )
 {
 	int ridx;

 	for ( ridx = 0; ridx < dev->nr_rates && dev->rates[ridx] != rate;
 	      ridx++ )
 		;
 	if ( ridx >= dev->nr_rates )
 		return;		/* couldn't find the rate */

 	rc80211_update ( dev, RX, ridx, retry, 0 );
 }

 /**
  * Free rate-control context
  *
  * @v ctx	Rate-control context
  */
 void rc80211_free ( struct rc80211_ctx *ctx )
 {
 	free ( ctx );
 }
	/*
	* Simple 802.11 rate-control algorithm for iPXE.
	*
	* Copyright (c) 2009 Joshua Oreman <oremanj@rwcr.net>.
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License as
	* published by the Free Software Foundation; either version 2 of the
	* License, or any later version.
	*
	* This program is distributed in the hope that it will be useful, but
	* WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write to the Free Software
	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
	* 02110-1301, USA.
	*/

	FILE_LICENCE ( GPL2_OR_LATER );

	#include <stdlib.h>
	#include <ipxe/net80211.h>

	/**
	* @file
	*
	* Simple 802.11 rate-control algorithm
	*/

	/** @page rc80211 Rate control philosophy
	*
	* We want to maximize our transmission speed, to the extent that we
	* can do that without dropping undue numbers of packets. We also
	* don't want to take up very much code space, so our algorithm has to
	* be pretty simple
	*
	* When we receive a packet, we know what rate it was transmitted at,
	* and whether it had to be retransmitted to get to us.
	*
	* When we send a packet, we hear back how many times it had to be
	* retried to get through, and whether it got through at all.
	*
	* Indications of TX success are more reliable than RX success, but RX
	* information helps us know where to start.
	*
	* To handle all of this, we keep for each rate and each direction (TX
	* and RX separately) some state information for the most recent
	* packets on that rate and the number of packets for which we have
	* information. The state is a 32-bit unsigned integer in which two
	* bits represent a packet: 11 if it went through well, 10 if it went
	* through with one retry, 01 if it went through with more than one
	* retry, or 00 if it didn't go through at all. We define the
	* "goodness" for a particular (rate, direction) combination as the
	* sum of all the 2-bit fields, times 33, divided by the number of
	* 2-bit fields containing valid information (16 except when we're
	* starting out). The number produced is between 0 and 99; we use -1
	* for rates with less than 4 RX packets or 1 TX, as an indicator that
	* we do not have enough information to rely on them.
	*
	* In deciding which rates are best, we find the weighted average of
	* TX and RX goodness, where the weighting is by number of packets
	* with data and TX packets are worth 4 times as much as RX packets.
	* The weighted average is called "net goodness" and is also a number
	* between 0 and 99. If 3 consecutive packets fail transmission
	* outright, we automatically ratchet down the rate; otherwise, we
	* switch to the best rate whenever the current rate's goodness falls
	* below some threshold, and try increasing our rate when the goodness
	* is very high.
	*
	* This system is optimized for iPXE's style of usage. Because normal
	* operation always involves receiving something, we'll make our way
	* to the best rate pretty quickly. We tend to follow the lead of the
	* sending AP in choosing rates, but we won't use rates for long that
	* don't work well for us in transmission. We assume iPXE won't be
	* running for long enough that rate patterns will change much, so we
	* don't have to keep time counters or the like. And if this doesn't
	* work well in practice there are many ways it could be tweaked.
	*
	* To avoid staying at 1Mbps for a long time, we don't track any
	* transmitted packets until we've set our rate based on received
	* packets.
	*/

	/** Two-bit packet status indicator for a packet with no retries */
	#define RC_PKT_OK 0x3

	/** Two-bit packet status indicator for a packet with one retry */
	#define RC_PKT_RETRIED_ONCE 0x2

	/** Two-bit packet status indicator for a TX packet with multiple retries
	*
	* It is not possible to tell whether an RX packet had one or multiple
	* retries; we rely instead on the fact that failed RX packets won't
	* get to us at all, so if we receive a lot of RX packets on a certain
	* rate it must be pretty good.
	*/
	#define RC_PKT_RETRIED_MULTI 0x1

	/** Two-bit packet status indicator for a TX packet that was never ACKed
	*
	* It is not possible to tell whether an RX packet was setn if it
	* didn't get through to us, but if we don't see one we won't increase
	* the goodness for its rate. This asymmetry is part of why TX packets
	* are weighted much more heavily than RX.
	*/
	#define RC_PKT_FAILED 0x0

	/** Number of times to weight TX packets more heavily than RX packets */
	#define RC_TX_FACTOR 4

	/** Number of consecutive failed TX packets that cause an automatic rate drop */
	#define RC_TX_EMERG_FAIL 3

	/** Minimum net goodness below which we will search for a better rate */
	#define RC_GOODNESS_MIN 85

	/** Maximum net goodness above which we will try to increase our rate */
	#define RC_GOODNESS_MAX 95

	/** Minimum (num RX + @c RC_TX_FACTOR * num TX) to use a certain rate */
	#define RC_UNCERTAINTY_THRESH 4

	/** TX direction */
	#define TX 0

	/** RX direction */
	#define RX 1

	/** A rate control context */
	struct rc80211_ctx
	{
	/** Goodness state for each rate, TX and RX */
	u32 goodness[2][NET80211_MAX_RATES];

	/** Number of packets recorded for each rate */
	u8 count[2][NET80211_MAX_RATES];

	/** Indication of whether we've set the device rate yet */
	int started;

	/** Counter of all packets sent and received */
	int packets;
	};

	/**
	* Initialize rate-control algorithm
	*
	* @v dev 802.11 device
	* @ret ctx Rate-control context, to be stored in @c dev->rctl
	*/
	struct rc80211_ctx * rc80211_init ( struct net80211_device *dev __unused )
	{
	struct rc80211_ctx ret = zalloc ( sizeof ( ret ) );
	return ret;
	}

	/**
	* Calculate net goodness for a certain rate
	*
	* @v ctx Rate-control context
	* @v rate_idx Index of rate to calculate net goodness for
	*/
	static int rc80211_calc_net_goodness ( struct rc80211_ctx *ctx,
	int rate_idx )
	{
	int sum[2], num[2], dir, pkt;

	for ( dir = 0; dir < 2; dir++ ) {
	u32 good = ctx->goodness[dir][rate_idx];

	num[dir] = ctx->count[dir][rate_idx];
	sum[dir] = 0;

	for ( pkt = 0; pkt < num[dir]; pkt++ )
	sum[dir] += ( good >> ( 2 * pkt ) ) & 0x3;
	}

	if ( ( num[TX] * RC_TX_FACTOR + num[RX] ) < RC_UNCERTAINTY_THRESH )
	return -1;

	return ( 33 * ( sum[TX] * RC_TX_FACTOR + sum[RX] ) /
	( num[TX] * RC_TX_FACTOR + num[RX] ) );
	}

	/**
	* Determine the best rate to switch to and return it
	*
	* @v dev 802.11 device
	* @ret rate_idx Index of the best rate to switch to
	*/
	static int rc80211_pick_best ( struct net80211_device *dev )
	{
	struct rc80211_ctx *ctx = dev->rctl;
	int best_net_good = 0, best_rate = -1, i;

	for ( i = 0; i < dev->nr_rates; i++ ) {
	int net_good = rc80211_calc_net_goodness ( ctx, i );

	if ( net_good > best_net_good \|\|
	( best_net_good > RC_GOODNESS_MIN &&
	net_good > RC_GOODNESS_MIN ) ) {
	best_net_good = net_good;
	best_rate = i;
	}
	}

	if ( best_rate >= 0 ) {
	int old_good = rc80211_calc_net_goodness ( ctx, dev->rate );
	if ( old_good != best_net_good )
	DBGC ( ctx, "802.11 RC %p switching from goodness "
	"%d to %d\n", ctx, old_good, best_net_good );

	ctx->started = 1;
	return best_rate;
	}

	return dev->rate;
	}

	/**
	* Set 802.11 device rate
	*
	* @v dev 802.11 device
	* @v rate_idx Index of rate to switch to
	*
	* This is a thin wrapper around net80211_set_rate_idx to insert a
	* debugging message where appropriate.
	*/
	static inline void rc80211_set_rate ( struct net80211_device *dev,
	int rate_idx )
	{
	DBGC ( dev->rctl, "802.11 RC %p changing rate %d->%d Mbps\n", dev->rctl,
	dev->rates[dev->rate] / 10, dev->rates[rate_idx] / 10 );

	net80211_set_rate_idx ( dev, rate_idx );
	}

	/**
	* Check rate-control state and change rate if necessary
	*
	* @v dev 802.11 device
	*/
	static void rc80211_maybe_set_new ( struct net80211_device *dev )
	{
	struct rc80211_ctx *ctx = dev->rctl;
	int net_good;

	net_good = rc80211_calc_net_goodness ( ctx, dev->rate );

	if ( ! ctx->started ) {
	rc80211_set_rate ( dev, rc80211_pick_best ( dev ) );
	return;
	}

	if ( net_good < 0 ) /* insufficient data */
	return;

	if ( net_good > RC_GOODNESS_MAX && dev->rate + 1 < dev->nr_rates ) {
	int higher = rc80211_calc_net_goodness ( ctx, dev->rate + 1 );
	if ( higher > net_good \|\| higher < 0 )
	rc80211_set_rate ( dev, dev->rate + 1 );
	else
	rc80211_set_rate ( dev, rc80211_pick_best ( dev ) );
	}

	if ( net_good < RC_GOODNESS_MIN ) {
	rc80211_set_rate ( dev, rc80211_pick_best ( dev ) );
	}
	}

	/**
	* Update rate-control state
	*
	* @v dev 802.11 device
	* @v direction One of the direction constants TX or RX
	* @v rate_idx Index of rate at which packet was sent or received
	* @v retries Number of times packet was retried before success
	* @v failed If nonzero, the packet failed to get through
	*/
	static void rc80211_update ( struct net80211_device *dev, int direction,
	int rate_idx, int retries, int failed )
	{
	struct rc80211_ctx *ctx = dev->rctl;
	u32 goodness = ctx->goodness[direction][rate_idx];

	if ( ctx->count[direction][rate_idx] < 16 )
	ctx->count[direction][rate_idx]++;

	goodness <<= 2;
	if ( failed )
	goodness \|= RC_PKT_FAILED;
	else if ( retries > 1 )
	goodness \|= RC_PKT_RETRIED_MULTI;
	else if ( retries )
	goodness \|= RC_PKT_RETRIED_ONCE;
	else
	goodness \|= RC_PKT_OK;

	ctx->goodness[direction][rate_idx] = goodness;

	ctx->packets++;

	rc80211_maybe_set_new ( dev );
	}

	/**
	* Update rate-control state for transmitted packet
	*
	* @v dev 802.11 device
	* @v retries Number of times packet was transmitted before success
	* @v rc Return status code for transmission
	*/
	void rc80211_update_tx ( struct net80211_device *dev, int retries, int rc )
	{
	struct rc80211_ctx *ctx = dev->rctl;

	if ( ! ctx->started )
	return;

	rc80211_update ( dev, TX, dev->rate, retries, rc );

	/* Check if the last RC_TX_EMERG_FAIL packets have all failed */
	if ( ! ( ctx->goodness[TX][dev->rate] &
	( ( 1 << ( 2 * RC_TX_EMERG_FAIL ) ) - 1 ) ) ) {
	if ( dev->rate == 0 )
	DBGC ( dev->rctl, "802.11 RC %p saw %d consecutive "
	"failed TX, but cannot lower rate any further\n",
	dev->rctl, RC_TX_EMERG_FAIL );
	else {
	DBGC ( dev->rctl, "802.11 RC %p lowering rate (%d->%d "
	"Mbps) due to %d consecutive TX failures\n",
	dev->rctl, dev->rates[dev->rate] / 10,
	dev->rates[dev->rate - 1] / 10,
	RC_TX_EMERG_FAIL );

	rc80211_set_rate ( dev, dev->rate - 1 );
	}
	}
	}

	/**
	* Update rate-control state for received packet
	*
	* @v dev 802.11 device
	* @v retry Whether the received packet had been retransmitted
	* @v rate Rate at which packet was received, in 100 kbps units
	*/
	void rc80211_update_rx ( struct net80211_device *dev, int retry, u16 rate )
	{
	int ridx;

	for ( ridx = 0; ridx < dev->nr_rates && dev->rates[ridx] != rate;
	ridx++ )
	;
	if ( ridx >= dev->nr_rates )
	return; /* couldn't find the rate */

	rc80211_update ( dev, RX, ridx, retry, 0 );
	}

	/**
	* Free rate-control context
	*
	* @v ctx Rate-control context
	*/
	void rc80211_free ( struct rc80211_ctx *ctx )
	{
	free ( ctx );
	}