[RFC] libertas: change quality calculation

[Holger Schurig]

I wasn't really satisfied with a graphical program that displayed
the link quality, the display was bit erratically. While changing
this, I noticed some other things which this and the next patch
addresses.

However, for this patch I'm not sure if it goes into the right
direction.


This changes the quality calculation for wireless statistics to
only consider signal & noise, but not number of tx-retries.
Also changes a the rather complicated formular for quality to be
more like http://www.ces.clemson.edu/linux/signal_quality.shtml.

Note that tx_retries are no longer used for the quality number. I
don't know of any other driver that does it, and tx_retries is
only increasing, so the quality would become smaller and 
smaller ...  which wouldn't reflect reality.

Questionable things:

I also found that the average noise floor is -86 dBm, not -96
dBm. So I changed this constant. Maybe this is wrong, what values 
do your cards report?

The wireless stats have SNR and noise floor to calcutate the
quality. However, the scanning logic (for "iwlist XXX scan") only
has a not-really-described dimensionless RSSI value. So the 
quality display for both outputs are a bit different, althought 
not too much. I don't know any good method, not even from above 
website, that would make both calculation results identical. 
However, this was also not the case with the old code.


Index: wireless-testing/drivers/net/wireless/libertas/wext.c
===================================================================
--- wireless-testing.orig/drivers/net/wireless/libertas/wext.c	
2008-03-18 13:42:42.000000000 +0100
+++ wireless-testing/drivers/net/wireless/libertas/wext.c	
2008-03-18 13:42:55.000000000 +0100
@@ -805,21 +805,8 @@ out:
 
 static struct iw_statistics *lbs_get_wireless_stats(struct 
net_device *dev)
 {
-	enum {
-		POOR = 30,
-		FAIR = 60,
-		GOOD = 80,
-		VERY_GOOD = 90,
-		EXCELLENT = 95,
-		PERFECT = 100
-	};
 	struct lbs_private *priv = dev->priv;
-	u32 rssi_qual;
-	u32 tx_qual;
-	u32 quality = 0;
 	int stats_valid = 0;
-	u8 rssi;
-	u32 tx_retries;
 	struct cmd_ds_802_11_get_log log;
 	u16 snr, nf;
 
@@ -838,24 +825,6 @@ static struct iw_statistics *lbs_get_wir
 	priv->wstats.qual.level = CAL_RSSI(snr, nf);
 	priv->wstats.qual.noise = CAL_NF(nf);
 
-	lbs_deb_wext("signal level %#x\n", priv->wstats.qual.level);
-	lbs_deb_wext("noise %#x\n", priv->wstats.qual.noise);
-
-	rssi = priv->wstats.qual.level - priv->wstats.qual.noise;
-	if (rssi < 15)
-		rssi_qual = rssi * POOR / 10;
-	else if (rssi < 20)
-		rssi_qual = (rssi - 15) * (FAIR - POOR) / 5 + POOR;
-	else if (rssi < 30)
-		rssi_qual = (rssi - 20) * (GOOD - FAIR) / 5 + FAIR;
-	else if (rssi < 40)
-		rssi_qual = (rssi - 30) * (VERY_GOOD - GOOD) /
-		    10 + GOOD;
-	else
-		rssi_qual = (rssi - 40) * (PERFECT - VERY_GOOD) /
-		    10 + VERY_GOOD;
-	quality = rssi_qual;
-
 	/* Quality by TX errors */
 	priv->wstats.discard.retries = priv->stats.tx_errors;
 
@@ -863,28 +832,19 @@ static struct iw_statistics *lbs_get_wir
 	log.hdr.size = cpu_to_le16(sizeof(log));
 	lbs_cmd_with_response(priv, CMD_802_11_GET_LOG, &log);
 
-	tx_retries = le32_to_cpu(log.retry);
-
-	if (tx_retries > 75)
-		tx_qual = (90 - tx_retries) * POOR / 15;
-	else if (tx_retries > 70)
-		tx_qual = (75 - tx_retries) * (FAIR - POOR) / 5 + POOR;
-	else if (tx_retries > 65)
-		tx_qual = (70 - tx_retries) * (GOOD - FAIR) / 5 + FAIR;
-	else if (tx_retries > 50)
-		tx_qual = (65 - tx_retries) * (VERY_GOOD - GOOD) /
-		    15 + GOOD;
-	else
-		tx_qual = (50 - tx_retries) *
-		    (PERFECT - VERY_GOOD) / 50 + VERY_GOOD;
-	quality = min(quality, tx_qual);
-
 	priv->wstats.discard.code = le32_to_cpu(log.wepundecryptable);
-	priv->wstats.discard.retries = tx_retries;
+	priv->wstats.discard.retries = le32_to_cpu(log.retry);
 	priv->wstats.discard.misc = le32_to_cpu(log.ackfailure);
 
 	/* Calculate quality */
-	priv->wstats.qual.qual = min_t(u8, quality, 100);
+	/* see http://www.ces.clemson.edu/linux/signal_quality.shtml */
+	snr = priv->wstats.qual.level  - priv->wstats.qual.noise;
+	if (snr <= 0)
+		priv->wstats.qual.qual = 0;
+	else if (snr >= 40)
+		priv->wstats.qual.qual = 100;
+	else
+		priv->wstats.qual.qual = 5*snr/2;
 	priv->wstats.qual.updated = IW_QUAL_ALL_UPDATED | IW_QUAL_DBM;
 	stats_valid = 1;
 
Index: wireless-testing/drivers/net/wireless/libertas/defs.h
===================================================================
--- wireless-testing.orig/drivers/net/wireless/libertas/defs.h	
2008-03-18 13:42:42.000000000 +0100
+++ wireless-testing/drivers/net/wireless/libertas/defs.h	
2008-03-18 13:42:55.000000000 +0100
@@ -208,12 +208,9 @@ static inline void lbs_deb_hex(unsigned 
 #define RxPD_MESH_FRAME RxPD_CONTROL_WDS_FRAME
 
 /** RSSI-related defines */
-/*	RSSI constants are used to implement 802.11 RSSI threshold
-*	indication. if the Rx packet signal got too weak for 5 
consecutive
-*	times, miniport driver (driver) will report this event to 
wrapper
-*/
 
-#define MRVDRV_NF_DEFAULT_SCAN_VALUE		(-96)
+/* This is the average noise level */
+#define MRVDRV_NF_DEFAULT_SCAN_VALUE		(-86)
 
 /** RTS/FRAG related defines */
 #define MRVDRV_RTS_MIN_VALUE		0