1 files changed, 112 insertions, 1 deletions
diff --git a/drivers/net/wireless/intel/iwlwifi/iwl-utils.c b/drivers/net/wireless/intel/iwlwifi/iwl-utils.c
index c5b49851e4b9..d503544fda40 100644
--- a/drivers/net/wireless/intel/iwlwifi/iwl-utils.c
+++ b/drivers/net/wireless/intel/iwlwifi/iwl-utils.c
@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause */
 /*
- * Copyright (C) 2024 Intel Corporation
+ * Copyright (C) 2024-2025 Intel Corporation
  */
 #include <net/gso.h>
 #include <linux/ieee80211.h>
@@ -82,3 +82,114 @@ int iwl_tx_tso_segment(struct sk_buff *skb, unsigned int num_subframes,
 }
 IWL_EXPORT_SYMBOL(iwl_tx_tso_segment);
 #endif /* CONFIG_INET */
+
+static u32 iwl_div_by_db(u32 value, u8 db)
+{
+	/*
+	 * 2^32 * 10**(i / 10) for i = [1, 10], skipping 0 and simply stopping
+	 * at 10 dB and looping instead of using a much larger table.
+	 *
+	 * Using 64 bit math is overkill, but means the helper does not require
+	 * a limit on the input range.
+	 */
+	static const u32 db_to_val[] = {
+		0xcb59185e, 0xa1866ba8, 0x804dce7a, 0x65ea59fe, 0x50f44d89,
+		0x404de61f, 0x331426af, 0x2892c18b, 0x203a7e5b, 0x1999999a,
+	};
+
+	while (value && db > 0) {
+		u8 change = min_t(u8, db, ARRAY_SIZE(db_to_val));
+
+		value = (((u64)value) * db_to_val[change - 1]) >> 32;
+
+		db -= change;
+	}
+
+	return value;
+}
+
+s8 iwl_average_neg_dbm(const u8 *neg_dbm_values, u8 len)
+{
+	int average_magnitude;
+	u32 average_factor;
+	int sum_magnitude = -128;
+	u32 sum_factor = 0;
+	int i, count = 0;
+
+	/*
+	 * To properly average the decibel values (signal values given in dBm)
+	 * we need to do the math in linear space.  Doing a linear average of
+	 * dB (dBm) values is a bit annoying though due to the large range of
+	 * at least -10 to -110 dBm that will not fit into a 32 bit integer.
+	 *
+	 * A 64 bit integer should be sufficient, but then we still have the
+	 * problem that there are no directly usable utility functions
+	 * available.
+	 *
+	 * So, lets not deal with that and instead do much of the calculation
+	 * with a 16.16 fixed point integer along with a base in dBm. 16.16 bit
+	 * gives us plenty of head-room for adding up a few values and even
+	 * doing some math on it. And the tail should be accurate enough too
+	 * (1/2^16 is somewhere around -48 dB, so effectively zero).
+	 *
+	 * i.e. the real value of sum is:
+	 *      sum = sum_factor / 2^16 * 10^(sum_magnitude / 10) mW
+	 *
+	 * However, that does mean we need to be able to bring two values to
+	 * a common base, so we need a helper for that.
+	 *
+	 * Note that this function takes an input with unsigned negative dBm
+	 * values but returns a signed dBm (i.e. a negative value).
+	 */
+
+	for (i = 0; i < len; i++) {
+		int val_magnitude;
+		u32 val_factor;
+
+		/* Assume invalid */
+		if (neg_dbm_values[i] == 0xff)
+			continue;
+
+		val_factor = 0x10000;
+		val_magnitude = -neg_dbm_values[i];
+
+		if (val_magnitude <= sum_magnitude) {
+			u8 div_db = sum_magnitude - val_magnitude;
+
+			val_factor = iwl_div_by_db(val_factor, div_db);
+			val_magnitude = sum_magnitude;
+		} else {
+			u8 div_db = val_magnitude - sum_magnitude;
+
+			sum_factor = iwl_div_by_db(sum_factor, div_db);
+			sum_magnitude = val_magnitude;
+		}
+
+		sum_factor += val_factor;
+		count++;
+	}
+
+	/* No valid noise measurement, return a very high noise level */
+	if (count == 0)
+		return 0;
+
+	average_magnitude = sum_magnitude;
+	average_factor = sum_factor / count;
+
+	/*
+	 * average_factor will be a number smaller than 1.0 (0x10000) at this
+	 * point. What we need to do now is to adjust average_magnitude so that
+	 * average_factor is between -0.5 dB and 0.5 dB.
+	 *
+	 * Just do -1 dB steps and find the point where
+	 *   -0.5 dB * -i dB = 0x10000 * 10^(-0.5/10) / i dB
+	 *                   = div_by_db(0xe429, i)
+	 * is smaller than average_factor.
+	 */
+	for (i = 0; average_factor < iwl_div_by_db(0xe429, i); i++) {
+		/* nothing */
+	}
+
+	return clamp(average_magnitude - i, -128, 0);
+}
+IWL_EXPORT_SYMBOL(iwl_average_neg_dbm);