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Commit 66679a65 authored by Lars Ericsson's avatar Lars Ericsson Committed by John W. Linville
Browse files

rt2x00: Fix rounding errors in RSSI average calculation 



Small changes in signal level was not detected up by the
MOVING_AVERAGE() due to a rounding error, using 'int' type.

rt2x00lib_antenna_diversity_eval:
rssi:	  -62 -62 -62 -62 -62 -62 -62 -62 -62 -62 -62 -62 -62 -62 -62
rssi_avg: -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57 -57

The signal level reported back could be significantly (5dBm)
different from the actual value. A level +3dBm is the same as
double the AP output power.

Signed-off-by: default avatarLars Ericsson <Lars_Ericsson@telia.com>
Signed-off-by: default avatarIvo van Doorn <IvDoorn@gmail.com>
Signed-off-by: default avatarJohn W. Linville <linville@tuxdriver.com>
parent 193df183

drivers/net/wireless/rt2x00/rt2x00.h

+13 −2
Original line number Original line Diff line number Diff line
@@ -133,6 +133,17 @@ 
#define SHORT_EIFS		( SIFS + SHORT_DIFS + \

#define SHORT_EIFS		( SIFS + SHORT_DIFS + \

				  GET_DURATION(IEEE80211_HEADER + ACK_SIZE, 10) )

				  GET_DURATION(IEEE80211_HEADER + ACK_SIZE, 10) )





/*

 * Structure for average calculation

 * The avg field contains the actual average value,

 * but avg_weight is internally used during calculations

 * to prevent rounding errors.

 */

struct avg_val {

	int avg;

	int avg_weight;

};



/*

/*

 * Chipset identification

 * Chipset identification

 * The chipset on the device is composed of a RT and RF chip.

 * The chipset on the device is composed of a RT and RF chip.
@@ -256,7 +267,7 @@ struct link_ant { 
	 * Similar to the avg_rssi in the link_qual structure

	 * Similar to the avg_rssi in the link_qual structure

	 * this value is updated by using the walking average.

	 * this value is updated by using the walking average.

	 */

	 */

	int rssi_ant;

	struct avg_val rssi_ant;

};

};





/*

/*
@@ -285,7 +296,7 @@ struct link { 
	/*

	/*

	 * Currently active average RSSI value

	 * Currently active average RSSI value

	 */

	 */

	int avg_rssi;

	struct avg_val avg_rssi;





	/*

	/*

	 * Currently precalculated percentages of successful

	 * Currently precalculated percentages of successful

drivers/net/wireless/rt2x00/rt2x00link.c

+39 −26
Original line number Original line Diff line number Diff line
@@ -46,7 +46,15 @@ 
#define DEFAULT_PERCENTAGE	50

#define DEFAULT_PERCENTAGE	50





/*

/*

 * Small helper macro to work with moving/walking averages.

 * Small helper macro for percentage calculation

 * This is a very simple macro with the only catch that it will

 * produce a default value in case no total value was provided.

 */

#define PERCENTAGE(__value, __total) \

	( (__total) ? (((__value) * 100) / (__total)) : (DEFAULT_PERCENTAGE) )



/*

 * Helper struct and macro to work with moving/walking averages.

 * When adding a value to the average value the following calculation

 * When adding a value to the average value the following calculation

 * is needed:

 * is needed:

 *

 *
@@ -60,18 +68,28 @@ 
 * for a few minutes but when the device is moved away from the AP

 * for a few minutes but when the device is moved away from the AP

 * the average will not decrease fast enough to compensate.

 * the average will not decrease fast enough to compensate.

 * The walking average compensates this and will move towards

 * The walking average compensates this and will move towards

 * the new values correctly allowing a effective link tuning.

 * the new values correctly allowing a effective link tuning,

 * the speed of the average moving towards other values depends

 * on the value for the number of samples. The higher the number

 * of samples, the slower the average will move.

 * We use two variables to keep track of the average value to

 * compensate for the rounding errors. This can be a significant

 * error (>5dBm) if the factor is too low.

 */

 */

#define MOVING_AVERAGE(__avg, __val, __samples) \

#define AVG_SAMPLES	8

	( (((__avg) * ((__samples) - 1)) + (__val)) / (__samples) )

#define AVG_FACTOR	1000



#define MOVING_AVERAGE(__avg, __val) \

/*

({ \

 * Small helper macro for percentage calculation

	struct avg_val __new; \

 * This is a very simple macro with the only catch that it will

	__new.avg_weight = \

 * produce a default value in case no total value was provided.

	    (__avg).avg_weight  ? \

 */

		((((__avg).avg_weight * ((AVG_SAMPLES) - 1)) + \

#define PERCENTAGE(__value, __total) \

		  ((__val) * (AVG_FACTOR))) / \

	( (__total) ? (((__value) * 100) / (__total)) : (DEFAULT_PERCENTAGE) )

		 (AVG_SAMPLES) ) : \

		((__val) * (AVG_FACTOR)); \

	__new.avg = __new.avg_weight / (AVG_FACTOR); \

	__new; \

})





/*

/*

 * For calculating the Signal quality we have determined

 * For calculating the Signal quality we have determined
@@ -98,8 +116,8 @@ static int rt2x00link_antenna_get_link_rssi(struct rt2x00_dev *rt2x00dev) 
{

{

	struct link_ant *ant = &rt2x00dev->link.ant;

	struct link_ant *ant = &rt2x00dev->link.ant;





	if (ant->rssi_ant && rt2x00dev->link.qual.rx_success)

	if (ant->rssi_ant.avg && rt2x00dev->link.qual.rx_success)

		return ant->rssi_ant;

		return ant->rssi_ant.avg;

	return DEFAULT_RSSI;

	return DEFAULT_RSSI;

}

}
@@ -121,7 +139,8 @@ static void rt2x00link_antenna_update_rssi_history(struct rt2x00_dev *rt2x00dev, 




static void rt2x00link_antenna_reset(struct rt2x00_dev *rt2x00dev)

static void rt2x00link_antenna_reset(struct rt2x00_dev *rt2x00dev)

{

{

	rt2x00dev->link.ant.rssi_ant = 0;

	rt2x00dev->link.ant.rssi_ant.avg = 0;

	rt2x00dev->link.ant.rssi_ant.avg_weight = 0;

}

}





static void rt2x00lib_antenna_diversity_sample(struct rt2x00_dev *rt2x00dev)

static void rt2x00lib_antenna_diversity_sample(struct rt2x00_dev *rt2x00dev)
@@ -258,8 +277,6 @@ void rt2x00link_update_stats(struct rt2x00_dev *rt2x00dev, 
	struct link_qual *qual = &rt2x00dev->link.qual;

	struct link_qual *qual = &rt2x00dev->link.qual;

	struct link_ant *ant = &rt2x00dev->link.ant;

	struct link_ant *ant = &rt2x00dev->link.ant;

	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;

	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)skb->data;

	int avg_rssi = rxdesc->rssi;

	int ant_rssi = rxdesc->rssi;





	/*

	/*

	 * Frame was received successfully since non-succesfull

	 * Frame was received successfully since non-succesfull
@@ -279,16 +296,12 @@ void rt2x00link_update_stats(struct rt2x00_dev *rt2x00dev, 
	/*

	/*

	 * Update global RSSI

	 * Update global RSSI

	 */

	 */

	if (link->avg_rssi)

	link->avg_rssi = MOVING_AVERAGE(link->avg_rssi, rxdesc->rssi);

		avg_rssi = MOVING_AVERAGE(link->avg_rssi, rxdesc->rssi, 8);

	link->avg_rssi = avg_rssi;





	/*

	/*

	 * Update antenna RSSI

	 * Update antenna RSSI

	 */

	 */

	if (ant->rssi_ant)

	ant->rssi_ant = MOVING_AVERAGE(ant->rssi_ant, rxdesc->rssi);

		ant_rssi = MOVING_AVERAGE(ant->rssi_ant, rxdesc->rssi, 8);

	ant->rssi_ant = ant_rssi;

}

}





static void rt2x00link_precalculate_signal(struct rt2x00_dev *rt2x00dev)

static void rt2x00link_precalculate_signal(struct rt2x00_dev *rt2x00dev)
@@ -421,10 +434,10 @@ static void rt2x00link_tuner(struct work_struct *work) 
	 * collect the RSSI data we could use this. Otherwise we

	 * collect the RSSI data we could use this. Otherwise we

	 * must fallback to the default RSSI value.

	 * must fallback to the default RSSI value.

	 */

	 */

	if (!link->avg_rssi || !qual->rx_success)

	if (!link->avg_rssi.avg || !qual->rx_success)

		qual->rssi = DEFAULT_RSSI;

		qual->rssi = DEFAULT_RSSI;

	else

	else

		qual->rssi = link->avg_rssi;

		qual->rssi = link->avg_rssi.avg;





	/*

	/*

	 * Only perform the link tuning when Link tuning

	 * Only perform the link tuning when Link tuning
@@ -442,7 +455,7 @@ static void rt2x00link_tuner(struct work_struct *work) 
	/*

	/*

	 * Send a signal to the led to update the led signal strength.

	 * Send a signal to the led to update the led signal strength.

	 */

	 */

	rt2x00leds_led_quality(rt2x00dev, link->avg_rssi);

	rt2x00leds_led_quality(rt2x00dev, qual->rssi);





	/*

	/*

	 * Evaluate antenna setup, make this the last step when

	 * Evaluate antenna setup, make this the last step when