gistfile1.c

/*
 * wireless_qual_to_percent
 *
 * Convert an iw_quality structure from SIOCGIWSTATS into a magical signal
 * strength percentage.
 *
 */
static int
wireless_qual_to_percent (const struct iw_quality *qual,
                          const struct iw_quality *max_qual)
{
	int percent = -1;
	int level_percent = -1;

	g_return_val_if_fail (qual != NULL, -1);
	g_return_val_if_fail (max_qual != NULL, -1);

	nm_log_dbg (LOGD_WIFI,
	            "QL: qual %d/%u/0x%X, level %d/%u/0x%X, noise %d/%u/0x%X, updated: 0x%X  ** MAX: qual %d/%u/0x%X, level %d/%u/0x%X, noise %d/%u/0x%X, updated: 0x%X",
	            (__s8) qual->qual, qual->qual, qual->qual,
	            (__s8) qual->level, qual->level, qual->level,
	            (__s8) qual->noise, qual->noise, qual->noise,
	            qual->updated,
	            (__s8) max_qual->qual, max_qual->qual, max_qual->qual,
	            (__s8) max_qual->level, max_qual->level, max_qual->level,
	            (__s8) max_qual->noise, max_qual->noise, max_qual->noise,
	            max_qual->updated);

	/* Try using the card's idea of the signal quality first as long as it tells us what the max quality is.
	 * Drivers that fill in quality values MUST treat them as percentages, ie the "Link Quality" MUST be 
	 * bounded by 0 and max_qual->qual, and MUST change in a linear fashion.  Within those bounds, drivers
	 * are free to use whatever they want to calculate "Link Quality".
	 */
	if ((max_qual->qual != 0) && !(max_qual->updated & IW_QUAL_QUAL_INVALID) && !(qual->updated & IW_QUAL_QUAL_INVALID))
		percent = (int)(100 * ((double)qual->qual / (double)max_qual->qual));

	/* If the driver doesn't specify a complete and valid quality, we have two options:
	 *
	 * 1) dBm: driver must specify max_qual->level = 0, and have valid values for
	 *        qual->level and (qual->noise OR max_qual->noise)
	 * 2) raw RSSI: driver must specify max_qual->level > 0, and have valid values for
	 *        qual->level and max_qual->level
	 *
	 * This is the WEXT spec.  If this interpretation is wrong, I'll fix it.  Otherwise,
	 * If drivers don't conform to it, they are wrong and need to be fixed.
	 */

	if (    (max_qual->level == 0) && !(max_qual->updated & IW_QUAL_LEVEL_INVALID)          /* Valid max_qual->level == 0 */
		&& !(qual->updated & IW_QUAL_LEVEL_INVALID)                                     /* Must have valid qual->level */
		&& (    ((max_qual->noise > 0) && !(max_qual->updated & IW_QUAL_NOISE_INVALID)) /* Must have valid max_qual->noise */
			|| ((qual->noise > 0) && !(qual->updated & IW_QUAL_NOISE_INVALID)))     /*    OR valid qual->noise */
	   ) {
		/* Absolute power values (dBm) */

		/* Reasonable fallbacks for dumb drivers that don't specify either level. */
		#define FALLBACK_NOISE_FLOOR_DBM  -90
		#define FALLBACK_SIGNAL_MAX_DBM   -20
		int max_level = FALLBACK_SIGNAL_MAX_DBM;
		int noise = FALLBACK_NOISE_FLOOR_DBM;
		int level = qual->level - 0x100;

		level = CLAMP (level, FALLBACK_NOISE_FLOOR_DBM, FALLBACK_SIGNAL_MAX_DBM);

		if ((qual->noise > 0) && !(qual->updated & IW_QUAL_NOISE_INVALID))
			noise = qual->noise - 0x100;
		else if ((max_qual->noise > 0) && !(max_qual->updated & IW_QUAL_NOISE_INVALID))
			noise = max_qual->noise - 0x100;
		noise = CLAMP (noise, FALLBACK_NOISE_FLOOR_DBM, FALLBACK_SIGNAL_MAX_DBM);

		/* A sort of signal-to-noise ratio calculation */
		level_percent = (int)(100 - 70 *(
		                                ((double)max_level - (double)level) /
		                                ((double)max_level - (double)noise)));
		nm_log_dbg (LOGD_WIFI, "QL1: level_percent is %d.  max_level %d, level %d, noise_floor %d.",
		            level_percent, max_level, level, noise);
	} else if (   (max_qual->level != 0)
	           && !(max_qual->updated & IW_QUAL_LEVEL_INVALID) /* Valid max_qual->level as upper bound */
	           && !(qual->updated & IW_QUAL_LEVEL_INVALID)) {
		/* Relative power values (RSSI) */

		int level = qual->level;

		/* Signal level is relavtive (0 -> max_qual->level) */
		level = CLAMP (level, 0, max_qual->level);
		level_percent = (int)(100 * ((double)level / (double)max_qual->level));
		nm_log_dbg (LOGD_WIFI, "QL2: level_percent is %d.  max_level %d, level %d.",
		            level_percent, max_qual->level, level);
	} else if (percent == -1) {
		nm_log_dbg (LOGD_WIFI, "QL: Could not get quality %% value from driver.  Driver is probably buggy.");
	}

	/* If the quality percent was 0 or doesn't exist, then try to use signal levels instead */
	if ((percent < 1) && (level_percent >= 0))
		percent = level_percent;

	nm_log_dbg (LOGD_WIFI, "QL: Final quality percent is %d (%d).",
	            percent, CLAMP (percent, 0, 100));
	return (CLAMP (percent, 0, 100));
}