linux/drivers/net/wireless/morsemicro/mm81x/mmrc.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) 2017-2026 Morse Micro
 */
#include "mmrc.h"

/*
 * The default packet size in bits used for calculated throughput of a given
 * rate
 */
#define DEFAULT_PACKET_SIZE_BITS 9600

/*
 * The default packet size in bytes used for calculating retries for a given
 * rate
 */
#define DEFAULT_PACKET_SIZE_BYTES 1200

/* The sample frequencies at different stages */
#define LOOKAROUND_RATE_INIT 5
#define LOOKAROUND_RATE_NORMAL 50
#define LOOKAROUND_RATE_STABLE 100

/* The thresholds for stability stages */
#define STABILITY_CNT_THRESHOLD_INIT 20
#define STABILITY_CNT_THRESHOLD_NORMAL 50
#define STABILITY_CNT_THRESHOLD_STABLE 100

/* The backoff step size for the counter */
#define STABILITY_BACKOFF_STEP 2

/*
 * The packet success threshold for attempting slower lookaround rates
 */
/*
 * Force a look around if there haven't been any for this number of cycles
 */
#define LOOKAROUND_MAX_RC_CYCLES 5

/*
 * Number of attempts for each lookaround rate within at most two RC cycles
 * if there are enough packets
 */
#define LOOKAROUND_RATE_ATTEMPTS 4

/*
 * Limit the number of times we try to pick a theoretically better rate to
 * sample. Necessary so we don't stall the CPU, due to constantly picking worse
 * rates.
 */
#define LOOKAROUND_FAIL_MAX 200

/*
 * Initial and reset probability per rate in the table
 * Changing this value will have a severe implication on the current heuristic
 * It could mean that some rates will have better probability throughput even
 * with no edivence and so will cause unexpected changes in the rate table
 */
#define RATE_INIT_PROBABILITY 0

/*
 * The lowest number of MPDUs within acknowledged AMPDUs that can be used for
 * rate stats
 */
#define AMPDU_STATS_MIN 2

/*
 * The lowest number of stats to be used for processing in NORMAL lookaround
 * mode
 */
#define STATS_MIN_NORMAL 2

/*
 * The lowest number of stats to be used for processing in INIT lookaround
 * mode
 */
#define STATS_MIN_INIT 1

/* The lowest probability value considered for recognising a dip */
#define PROBABILITY_DIP_MIN 20

/* The lowest probability value for recovering from a dip */
#define PROBABILITY_DIP_RECOVERY_MIN 40

/*
 * The time cap on rate allocation for multiple attempts. If a single attempt
 * exceeds this window, no additional attempts will be generated
 */
#define MAX_WINDOW_ATTEMPT_TIME 4000

/* The time window for all rates in rate table */
#define RATE_WINDOW_MICROSECONDS 24000

/*
 * EWMA is the alpha coefficient in the exponential weighting moving average
 * filter used for probability updates.
 *
 * Y[n] = X[n] * (100 - EWMA) + (Y[n-1] * EWMA)
 *	  -------------------------------------
 *			   100
 *
 */
#define EWMA 75

/*
 * Evidence scaling to allow for one decimal place. Needed for low
 * throughput, otherwise the history decays in a single cycle.
 */
#define EVIDENCE_SCALE 5

/*
 * Evidence maximum to ensure history doesn't decay too slowly when
 * there is a lot of historical data.
 */
#define EVIDENCE_MAX 100

/*
 * This fixed point conversion multiplies a value by one and shifts it
 * accordingly to account for the fixed point shifting at the return of a
 * function
 */
#define FP_8_MULT_1 256

/* Fixed point conversion for 2.1 * 2^8 used for 4MHz symbol multiplication */
#define FP_8_4MHZ 537

/* Fixed point conversion for 4.5 * 2^8 used for 8MHz symbol multiplication */
#define FP_8_8MHZ 1152

/* Fixed point conversion for 9.0 * 2^8 used for 16MHz symbol multiplication */
#define FP_8_16MHZ 2301

/*
 * Fixed point conversion for 3.6 * 2^8 used for long guard symbol tx time
 * multiplication
 */
#define FP_8_LONG_GUARD_SYMBOL_TIME 1024

/*
 * Fixed point conversion for 4.0 * 2^8 used for short guard symbol tx time
 * multiplication
 */
#define FP_8_SHORT_GUARD_SYMBOL_TIME 921

/*
 * Shift value to shift back our FP conversions
 */
#define FP_8_SHIFT 8

/*
 * Limit to count of consecutive variations in one direction
 */
#define MAX_VARIATION_DIRECTION 5

/*
 * Threshold for considering consecutive variation direction as variation
 * or not
 */
#define VARIATION_DIRECTION_THRESHOLD 3

/* EWMA percentage value for averaging the best rate probability variation */
#define VARIATION_EWMA 95

/* Percentage variation regarded as minor */
#define MINOR_VARIATION_THRESHOLD 1

/* Percentage variation regarded as moderate */
#define MODERATE_VARIATION_THRESHOLD 3

/* Percentage variation regarded as significant */
#define SIGNIFICANT_VARIATION_THRESHOLD 5

/* If the best rate changes twice in this number of cycles, it is unstable */
#define BEST_RATE_UNSTABLE_THRESHOLD 4

/*
 * Once the best rate is unchanged for this number of cycles it has
 * converged
 */
#define BEST_RATE_CONVERGED_THRESHOLD 10

/* RSSI threshold for short range */
#define MMRC_SHORT_RANGE_RSSI_LIMIT -70

/* RSSI threshold for mid range */
#define MMRC_MID_RANGE_RSSI_LIMIT -85

#define MMRC_MAX_BW(bw_caps)                                \
	(((bw_caps) & BIT(MMRC_BW_16MHZ)) ? MMRC_BW_16MHZ : \
	 ((bw_caps) & BIT(MMRC_BW_8MHZ))  ? MMRC_BW_8MHZ :  \
	 ((bw_caps) & BIT(MMRC_BW_4MHZ))  ? MMRC_BW_4MHZ :  \
	 ((bw_caps) & BIT(MMRC_BW_2MHZ))  ? MMRC_BW_2MHZ :  \
					    MMRC_BW_1MHZ)

/*
 * This table stores the number of bits per symbols used for MCS0-MCS9 based
 * on 20MHz and 1SS
 */
static const u32 sym_table[10] = { 24, 36, 48, 72, 96, 144, 192, 216, 256, 288 };

/*
 * Calculate which bit is the nth bit set in an integer based flag.
 */
static u8 nth_bit(u16 in, u16 index)
{
	u32 i;
	u8 count = 0;

	for (i = 0; count != index + 1; i++) {
		if (((1u << i) & in) != 0)
			count++;
	}

	return i - 1;
}

/*
 * Calculate the input bit's index among all the set bits in an integer
 * based flag.
 */
static u16 bit_index(u16 in, u32 bit_pos)
{
	u16 i;
	u16 index = 0;

	for (i = 0; i != bit_pos + 1; i++) {
		if (((1u << i) & in) != 0)
			index++;
	}

	if (index == 0) {
		/* Could not match bit pos to caps */
		return 0;
	}

	return index - 1;
}

static u16 rows_from_sta_caps(struct mmrc_sta_capabilities *caps)
{
	u16 rows = 0;
	u8 n_rates = hweight_long(caps->rates);

	/* Taking MCS10 into account as it is relevant for 1 MHz entries */
	if (caps->rates & BIT(MMRC_MCS10)) {
		n_rates -= 1;
		rows = 2;
	}

	rows += (hweight_long(caps->bandwidth) * n_rates *
		 hweight_long(caps->guard) *
		 hweight_long(caps->spatial_streams));

	return rows;
}

static void rate_update_index(struct mmrc_table *tb, struct mmrc_rate *rate)
{
	u16 index = 0;
	/* Information about our rates */
	u16 bw = hweight_long(tb->caps.bandwidth);
	u16 streams = hweight_long(tb->caps.spatial_streams);
	u16 guard = hweight_long(tb->caps.guard);
	u16 rows = rows_from_sta_caps(&tb->caps);

	index = bit_index(tb->caps.guard, rate->guard) +
		bit_index(tb->caps.bandwidth, rate->bw) * guard +
		bit_index(tb->caps.spatial_streams, rate->ss) * guard * bw +
		bit_index(tb->caps.rates, rate->rate) * bw * streams * guard;

	if (index >= rows)
		index = 0;

	rate->index = index;
}

static struct mmrc_rate get_rate_row(struct mmrc_table *tb, u16 index)
{
	struct mmrc_rate rate;
	u16 ss_index;

	/* Information about our rates */
	u16 mcs = hweight_long(tb->caps.rates);
	u16 bw = hweight_long(tb->caps.bandwidth);
	u16 streams = hweight_long(tb->caps.spatial_streams);
	u16 guard = hweight_long(tb->caps.guard);
	u16 total_caps = mcs * bw * streams * guard;

	/* Find our MCS */
	u16 rows = total_caps / mcs;
	u16 mcs_index = index / rows;
	u16 mcs_modulo = index % rows;

	mcs = nth_bit(tb->caps.rates, mcs_index);

	/* Find our spatial stream */
	rows = rows / streams;
	streams = nth_bit(tb->caps.spatial_streams, mcs_modulo / rows);

	/* Find our bandwidth */
	ss_index = index % rows;
	rows = rows / bw;
	bw = nth_bit(tb->caps.bandwidth, ss_index / rows);

	/* Find our guard */
	guard = nth_bit(tb->caps.guard, index % guard);

	/* Add range checks to keep scan-build happy */
	if (bw >= MMRC_BW_MAX)
		bw = MMRC_BW_1MHZ;

	if (guard >= MMRC_GUARD_MAX)
		guard = MMRC_GUARD_LONG;

	/* Validate guard against capability */
	if (guard == MMRC_GUARD_SHORT &&
	    !(tb->caps.sgi_per_bw & SGI_PER_BW(bw)))
		guard = MMRC_GUARD_LONG;

	/* Create our rate row and send it */
	rate.bw = MMRC_BW_TO_BITFIELD(bw);
	rate.ss = MMRC_SS_TO_BITFIELD(streams);
	rate.rate = MMRC_RATE_TO_BITFIELD(mcs);
	rate.guard = MMRC_GUARD_TO_BITFIELD(guard);
	rate.attempts = 0;
	rate.flags = 0;

	/* Update index as bw or guard may have changed */
	rate_update_index(tb, &rate);

	return rate;
}

size_t mmrc_memory_required_for_caps(struct mmrc_sta_capabilities *caps)
{
	return sizeof(struct mmrc_table) +
	       rows_from_sta_caps(caps) * sizeof(struct mmrc_stats_table);
}

static u32 calculate_bits_per_symbol(struct mmrc_rate *rate)
{
	u32 bps;

	/* If MCS10 is selected we return 2*MCS0 Symbols */
	if (rate->rate == MMRC_MCS10)
		return 6;

	/* Confirm that the rate is valid for the sym_table lookup */
	if (rate->rate >= MMRC_MCS_UNUSED) {
		pr_err("%s: Invalid MCS rate %d for sym_table lookup\n",
		       __func__, rate->rate);
		return 1;
	}

	/*
	 * Coversion from 20MHz as in sym_table to:
	 * 40MHz   ==	x 2.1
	 * 80MHz   ==	x 4.5
	 * 160MHz  ==	x 9.0
	 */
	bps = sym_table[rate->rate];
	switch (rate->bw) {
	case (MMRC_BW_4MHZ):
		bps *= FP_8_4MHZ;
		break;
	case (MMRC_BW_8MHZ):
		bps *= FP_8_8MHZ;
		break;
	case (MMRC_BW_16MHZ):
		bps *= FP_8_16MHZ;
		break;
	case (MMRC_BW_1MHZ):
		bps = sym_table[rate->rate] * 24 / 52;
		bps *= FP_8_MULT_1;
		break;
	case (MMRC_BW_2MHZ):
	case (MMRC_BW_MAX):
	default:
		bps *= FP_8_MULT_1;
		break;
	}
	/* SS + 1 because mmrc_spatial_stream starts at 0 */
	return ((rate->ss + 1) * bps) >> FP_8_SHIFT;
}

static u32 get_tx_time(struct mmrc_rate *rate)
{
	u32 tx = 0;
	u32 n_sym;
	u32 avg_bits;

	/* Calculate tx time based on a default packet size */
	avg_bits = DEFAULT_PACKET_SIZE_BITS;

	/* Number of bits per symbol for this rate */
	n_sym = calculate_bits_per_symbol(rate);

	/* In case of bad calcuation/parameter use lowest value */
	n_sym = n_sym == 0 ? sym_table[0] : n_sym;

	/* number of symbols in default packet size */
	n_sym = avg_bits / n_sym;

	/* tx is time to transmit average packet in us */
	switch (rate->guard) {
	case (MMRC_GUARD_LONG):
		tx = n_sym * FP_8_LONG_GUARD_SYMBOL_TIME;
		break;
	case (MMRC_GUARD_SHORT):
		tx = n_sym * FP_8_SHORT_GUARD_SYMBOL_TIME;
		break;
	default:
		return 0;
	}

	return (tx * 10) >> FP_8_SHIFT;
}

u32 mmrc_calculate_theoretical_throughput(struct mmrc_rate rate)
{
	static const u32 s1g_tpt_lgi[4][11] = {
		{ 300, 600, 900, 1200, 1800, 2400, 2700, 3000, 3600, 4000,
		  150 },
		{ 650, 1300, 1950, 2600, 3900, 5200, 5850, 6500, 7800, 0, 0 },
		{ 1350, 2700, 4050, 5400, 8100, 10800, 12150, 13500, 16200,
		  18000, 0 },
		{ 2925, 5850, 8775, 11700, 17550, 23400, 26325, 29250, 35100,
		  39000, 0 },
	};

	static const u32 s1g_tpt_sgi[4][11] = {
		{ 333, 666, 1000, 1333, 2000, 2666, 3000, 3333, 4000, 4444,
		  166 },
		{ 722, 1444, 2166, 2888, 4333, 5777, 6500, 7222, 8666, 0, 0 },
		{ 1500, 3000, 4500, 6000, 9000, 12000, 13500, 15000, 18000,
		  20000, 0 },
		{ 3250, 6500, 9750, 13000, 19500, 26000, 29250, 32500, 39000,
		  43333, 0 },
	};

	if (rate.guard)
		return s1g_tpt_sgi[rate.bw][rate.rate] * 1000 * (rate.ss + 1);

	return s1g_tpt_lgi[rate.bw][rate.rate] * 1000 * (rate.ss + 1);
}

static u32 calculate_throughput(struct mmrc_table *tb, u8 index)
{
	struct mmrc_rate rate = get_rate_row(tb, index);

	/*
	 * Avoid the overflow (observed for 8MHz MCS9 rate: 43333) by dividing
	 * first before multiplying. Should not experience any loss of
	 * precision as the throughput is already multiplied by 1000 in
	 * mmrc_calculate_theoretical_throughput (returned as bits/sec)
	 */
	if (tb->table[rate.index].prob < 10)
		return 0;
	else if (rate.index == tb->best_tp.index && tb->interference_likely)
		/*
		 * Assist the best rate by increasing the probability by the
		 * averaged variation
		 */
		return (mmrc_calculate_theoretical_throughput(rate) / 100) *
		       (tb->table[rate.index].prob + tb->probability_variation);
	else
		return (mmrc_calculate_theoretical_throughput(rate) / 100) *
		       tb->table[rate.index].prob;
}

static bool validate_rate(struct mmrc_table *tb, struct mmrc_rate *rate)
{
	if (rate->rate == MMRC_MCS10 &&
	    (rate->bw != MMRC_BW_1MHZ || rate->ss != MMRC_SPATIAL_STREAM_1)) {
		/*
		 * 802.11ah does not support MCS10 with BW that is not 1MHz or
		 * not 1 spatial stream.
		 */
		return false;
	}

	if (rate->rate == MMRC_MCS9 && rate->bw == MMRC_BW_2MHZ &&
	    rate->ss != MMRC_SPATIAL_STREAM_3) {
		/*
		 * 802.11ah does not support MCS9 at 2MHz for 1, 2 or 4 spatial
		 * streams
		 */
		return false;
	}

	if (rate->guard == MMRC_GUARD_SHORT &&
	    !(tb->caps.sgi_per_bw & SGI_PER_BW(rate->bw)))
		return false;

	return true;
}

static u16 find_baseline_index(struct mmrc_table *tb)
{
	u32 i, theoretical_tp, min_theoretical_tp;
	u16 row_count = rows_from_sta_caps(&tb->caps);
	u16 min_theoretical_tp_index = 0;
	struct mmrc_rate rate;

	if (tb->caps.rates & BIT(MMRC_MCS10))
		return 0;

	min_theoretical_tp =
		mmrc_calculate_theoretical_throughput(get_rate_row(tb, 0));
	for (i = 0; i < row_count; i++) {
		rate = get_rate_row(tb, i);
		if (!validate_rate(tb, &rate))
			continue;

		theoretical_tp = mmrc_calculate_theoretical_throughput(rate);
		if (min_theoretical_tp > theoretical_tp) {
			min_theoretical_tp = theoretical_tp;
			min_theoretical_tp_index = rate.index;
		}
	}

	return min_theoretical_tp_index;
}

/*
 * Fill out the remaining rates to be used once the best rate is selected.
 * Normally the retry rates are one MCS lower than the previous, however in
 * unconverged mode we limit the 3 respective retry rates to MCS 4, 2 and 0
 * respectively. The last retry rate is always MCS 0
 */
static void mmrc_fill_retry_rates(struct mmrc_table *tb)
{
	tb->second_tp = tb->best_tp;
	if (tb->second_tp.rate != MMRC_MCS0) {
		tb->second_tp.rate--;
		if (tb->unconverged && tb->second_tp.rate > MMRC_MCS4)
			tb->second_tp.rate = MMRC_MCS4;
		rate_update_index(tb, &tb->second_tp);
	} else if (tb->second_tp.bw > MMRC_BW_1MHZ) {
		tb->second_tp.bw--;
		rate_update_index(tb, &tb->second_tp);
	}

	tb->best_prob = tb->second_tp;
	if (tb->best_prob.rate != MMRC_MCS0) {
		tb->best_prob.rate--;
		if (tb->unconverged && tb->best_prob.rate > MMRC_MCS2)
			tb->best_prob.rate = MMRC_MCS2;
		rate_update_index(tb, &tb->best_prob);
	} else if (tb->best_prob.bw > MMRC_BW_1MHZ) {
		tb->best_prob.bw--;
		rate_update_index(tb, &tb->best_prob);
	}

	tb->baseline = tb->best_prob;
	if (tb->baseline.rate != MMRC_MCS0) {
		tb->baseline.rate = MMRC_MCS0;
		rate_update_index(tb, &tb->baseline);
	} else if (tb->baseline.bw > MMRC_BW_1MHZ) {
		tb->baseline.bw--;
		rate_update_index(tb, &tb->baseline);
	}
}

/*
 * Updates the mmrc_table with the appropriate rate priority based on the
 * latest update statistics
 */
static void generate_table_priority(struct mmrc_table *tb, u32 new_stats)
{
	u16 i;
	u16 best_row = tb->best_tp.index;
	u16 prev_best_row = best_row;
	u8 prev_best_rate = tb->best_tp.rate;
	u16 second_best_row = tb->second_tp.index;
	u32 best_tp = calculate_throughput(tb, best_row);
	u32 second_best_tp = calculate_throughput(tb, second_best_row);
	u32 last_nonzero_prob = 0;
	struct mmrc_rate tmp;
	u32 tmp_tp;

	/* Use fixed rate if set */
	if (tb->fixed_rate.rate != MMRC_MCS_UNUSED) {
		tb->best_tp = tb->fixed_rate;
		tb->second_tp = tb->fixed_rate;
		tb->best_prob = tb->fixed_rate;
		return;
	}

	for (i = 0; i < rows_from_sta_caps(&tb->caps); i++) {
		tmp = get_rate_row(tb, i);
		if (!validate_rate(tb, &tmp))
			continue;

		if (tb->table[tmp.index].evidence == 0)
			continue;

		/*
		 * Besides better throughput, also consider this rate better if
		 * lower rates had worse probability. That indicates the rate
		 * itself is not the problem. Only do the probability check for
		 * rates up to the previous best rate.
		 */
		tmp_tp = calculate_throughput(tb, tmp.index);

		if (tmp_tp > best_tp ||
		    (tb->table[tmp.index].max_throughput <=
			     tb->table[prev_best_row].max_throughput &&
		     tb->table[tmp.index].prob >=
			     PROBABILITY_DIP_RECOVERY_MIN &&
		     tb->table[tmp.index].prob >
			     tb->table[last_nonzero_prob].prob)) {
			second_best_row = best_row;
			second_best_tp = best_tp;

			best_tp = tmp_tp;
			best_row = tmp.index;
		} else if (tmp_tp > second_best_tp && best_row != tmp.index) {
			second_best_tp = tmp_tp;
			second_best_row = tmp.index;
		}

		if (tb->table[tmp.index].prob >= PROBABILITY_DIP_MIN &&
		    tb->table[tmp.index].max_throughput >=
			    tb->table[last_nonzero_prob].max_throughput)
			last_nonzero_prob = tmp.index;
	}

	/* Only update rates and stability when there are new statistics */
	if (!new_stats)
		return;

	tb->best_tp = get_rate_row(tb, best_row);
	if (best_tp == 0 && tb->best_tp.rate > MMRC_MCS0) {
		/* Drop one rate, as the best throughput is zero */
		tb->best_tp.rate--;
		rate_update_index(tb, &tb->best_tp);
	}
	tb->second_tp = get_rate_row(tb, second_best_row);
	mmrc_fill_retry_rates(tb);

	if (tb->best_tp.rate > MMRC_MCS1 && prev_best_row == best_row) {
		/* Increase the counter when the best rate is not changed */
		tb->stability_cnt++;
	} else if (tb->stability_cnt > STABILITY_BACKOFF_STEP) {
		/* Back off the counter when there is a new best rate */
		tb->stability_cnt -= STABILITY_BACKOFF_STEP;
	} else {
		tb->stability_cnt = 0;
	}

	if (prev_best_row != best_row) {
		s8 latest_best_rate_diff = prev_best_rate - tb->best_tp.rate;
		u8 total_abs_best_rate_diff =
			abs(tb->best_rate_diff[0] + tb->best_rate_diff[1] +
			    latest_best_rate_diff);

		if (!tb->interference_likely) {
			tb->probability_variation = 0;
			if (!tb->unconverged &&
			    tb->best_rate_cycle_count <=
				    BEST_RATE_UNSTABLE_THRESHOLD &&
			    total_abs_best_rate_diff >= 2) {
				/*
				 * Best rate has changed twice in a few cycles
				 * and moved at least 2 MCSs from where it was
				 * 3 best rate changes ago
				 */
				tb->unconverged = true;
				tb->newly_unconverged = true;
			}
		}
		if (tb->unconverged && !tb->newly_unconverged &&
		    total_abs_best_rate_diff < 2) {
			/*
			 * Best rate has been relatively stable (not moved more
			 * than 1 MCS after the last 3 rate changes), go back
			 * to converged
			 */
			tb->unconverged = false;
		}
		tb->probability_variation_direction = 0;
		tb->best_rate_cycle_count = 0;
		tb->best_rate_diff[0] = tb->best_rate_diff[1];
		tb->best_rate_diff[1] = latest_best_rate_diff;
	} else {
		tb->best_rate_cycle_count++;
		if (tb->unconverged && !tb->newly_unconverged &&
		    tb->best_rate_cycle_count >=
			    BEST_RATE_CONVERGED_THRESHOLD) {
			/*
			 * Best rate has been stable for a while, go back to
			 * converged
			 */
			tb->unconverged = false;
		}
	}

	if (tb->newly_unconverged)
		tb->newly_unconverged = false;
}

static u32 calculate_attempt_time(struct mmrc_rate *rate, size_t size)
{
	u32 time;

	time = get_tx_time(rate);

	if (size > DEFAULT_PACKET_SIZE_BYTES)
		time = (time * ((size * 1000) / DEFAULT_PACKET_SIZE_BYTES)) /
		       1000;
	else
		time = (time * 1000) /
		       ((DEFAULT_PACKET_SIZE_BYTES * 1000) / size);

	return time;
}

u32 mmrc_calculate_rate_tx_time(struct mmrc_rate *rate, size_t size)
{
	u8 i;
	u32 total_time = 0;

	for (i = 0; i < rate->attempts; i++)
		total_time += calculate_attempt_time(rate, size);

	return total_time;
}

/*
 * Calculates the appropriate amount of additional attempts to make based on
 * packet size and theoretical throughput.
 */
static void calculate_remaining_attempts(struct mmrc_table *tb,
					 struct mmrc_rate_table *rate,
					 s32 *rem_time, size_t size)
{
	size_t i;

	if (*rem_time <= 0)
		return;

	for (i = 0; i < MMRC_MAX_CHAIN_LENGTH; i++) {
		u32 attempt_time;
		u32 attempt;

		if (rate->rates[i].rate == MMRC_MCS_UNUSED)
			break;

		/*
		 * The attempts for these rates were calculated in the initial
		 * attempt allocation
		 */
		if (tb->table[rate->rates[i].index].prob < 20)
			continue;

		if (i == 0 && (calculate_throughput(tb, rate->rates[i].index) <
			       calculate_throughput(tb, tb->best_prob.index)))
			continue;

		attempt_time = calculate_attempt_time(&rate->rates[i], size);
		if (!attempt_time)
			continue;

		attempt = (*rem_time / tb->caps.max_rates) / attempt_time;
		attempt += rate->rates[i].attempts;

		rate->rates[i].attempts = MMRC_ATTEMPTS_TO_BITFIELD(
			attempt > MMRC_MAX_CHAIN_ATTEMPTS ?
				MMRC_MAX_CHAIN_ATTEMPTS :
				attempt);
	}
}

/* Allocate initial attempts to all rates in a rate table */
static void allocate_initial_attempts(struct mmrc_rate_table *rate,
				      s32 *rem_time, size_t size)
{
	u32 i;

	for (i = 0; i < MMRC_MAX_CHAIN_LENGTH; i++) {
		u32 attempt_time;

		if (rate->rates[i].rate == MMRC_MCS_UNUSED)
			break;

		attempt_time = calculate_attempt_time(&rate->rates[i], size);

		/*
		 * if the time for a single attempt is very long, lets just
		 * try once
		 */
		if (attempt_time > MAX_WINDOW_ATTEMPT_TIME) {
			*rem_time -= attempt_time;
			rate->rates[i].attempts = MMRC_ATTEMPTS_TO_BITFIELD(1);
		} else {
			*rem_time -= attempt_time * 2;
			rate->rates[i].attempts = MMRC_ATTEMPTS_TO_BITFIELD(2);
		}
	}
}

void mmrc_get_rates(struct mmrc_table *tb, struct mmrc_rate_table *out,
		    size_t size)
{
	u8 i;
	u16 random_index;
	struct mmrc_rate random;
	struct mmrc_rate lookaround0 = tb->best_tp;
	struct mmrc_rate lookaround1 = tb->second_tp;
	bool is_lookaround;
	int lookaround_index = -1;
	int best_index = 0;
	int random_tp = 0;
	int best_tp;
	int lookaround_fail_count;
	bool try_current_lookaround = false;

	s32 rem_time = RATE_WINDOW_MICROSECONDS;

	memset(out, 0, sizeof(*out));

	tb->lookaround_cnt = (tb->lookaround_cnt + 1) % tb->lookaround_wrap;
	/*
	 * Look around if the counter wraps or there has been no look around
	 * for a number of rate control cycles.
	 */
	is_lookaround = (tb->fixed_rate.rate == MMRC_MCS_UNUSED) &&
			((tb->lookaround_cnt == 0) ||
			 ((tb->last_lookaround_cycle +
			   LOOKAROUND_MAX_RC_CYCLES) <= tb->cycle_cnt));

	/* Also skip sampling if we don't yet have data for our best rate */
	if (tb->table[tb->best_tp.index].evidence == 0)
		is_lookaround = false;

	if (tb->lookaround_wrap != LOOKAROUND_RATE_STABLE) {
		if (tb->stability_cnt >= tb->stability_cnt_threshold) {
			tb->lookaround_wrap = LOOKAROUND_RATE_STABLE;
			tb->stability_cnt_threshold =
				STABILITY_CNT_THRESHOLD_STABLE;
			tb->stability_cnt = STABILITY_CNT_THRESHOLD_STABLE * 2;
			is_lookaround = false;
		}
	} else if (tb->stability_cnt < tb->stability_cnt_threshold) {
		tb->stability_cnt_threshold = STABILITY_CNT_THRESHOLD_NORMAL;
		tb->lookaround_wrap = LOOKAROUND_RATE_NORMAL;
		tb->stability_cnt = 0;
	}

	/* Look around only when the fixed rate is not set */
	if (is_lookaround) {
		tb->total_lookaround++;
		tb->forced_lookaround =
			(tb->forced_lookaround + 1) % LOOKAROUND_RATE_NORMAL;
		tb->last_lookaround_cycle = tb->cycle_cnt;

		if (tb->current_lookaround_rate_attempts <
		    LOOKAROUND_RATE_ATTEMPTS)
			try_current_lookaround = true;

		best_tp = calculate_throughput(tb, tb->best_tp.index);

		for (lookaround_fail_count = 0;
		     lookaround_fail_count < LOOKAROUND_FAIL_MAX;
		     lookaround_fail_count++) {
			if (try_current_lookaround) {
				random_index =
					tb->current_lookaround_rate_index;
				try_current_lookaround = false;
			} else {
				random_index = get_random_u32_below(
					rows_from_sta_caps(&tb->caps));
			}
			random = get_rate_row(tb, random_index);

			if (!validate_rate(tb, &random))
				continue;

			if (random.rate == MMRC_MCS10)
				continue;

			if (tb->table[random_index].evidence > 0)
				random_tp =
					calculate_throughput(tb, random_index);
			else
				random_tp =
					mmrc_calculate_theoretical_throughput(
						random);

			/*
			 * Skip rates that can only be worse than the current
			 * best
			 */
			if (random_tp <= best_tp)
				continue;

			/*
			 * Force looking up the rate no more that one MCS.
			 * It will avoid looking for rates with very low
			 * success rate. In case of better environment
			 * conditions MMRC will collect enough statistics to
			 * climb up the rates one by one.
			 */
			if (random.rate > tb->best_tp.rate + 1 ||
			    random.bw > tb->best_tp.bw + 1 ||
			    (random.rate > tb->best_tp.rate &&
			     random.bw > tb->best_tp.bw))
				continue;

			if (tb->current_lookaround_rate_index == random_index) {
				tb->current_lookaround_rate_attempts++;
			} else {
				tb->current_lookaround_rate_attempts = 0;
				tb->current_lookaround_rate_index =
					random_index;
			}

			break;
		}

		if (lookaround_fail_count >= LOOKAROUND_FAIL_MAX) {
			is_lookaround = false;
			tb->current_lookaround_rate_index = tb->best_tp.index;
		} else {
			lookaround0 = random;
			lookaround1 = tb->best_tp;
			lookaround_index = 0;
			best_index = 1;
		}
	}

	if (tb->caps.max_rates == 1) {
		out->rates[0] = (is_lookaround) ? lookaround0 : tb->best_tp;
		out->rates[1].rate = MMRC_MCS_UNUSED;
		out->rates[2].rate = MMRC_MCS_UNUSED;
		out->rates[3].rate = MMRC_MCS_UNUSED;
	} else if (tb->caps.max_rates == 2) {
		out->rates[0] = (is_lookaround) ? lookaround0 : tb->best_tp;
		out->rates[1] = (is_lookaround) ? lookaround1 : tb->best_prob;
		out->rates[2].rate = MMRC_MCS_UNUSED;
		out->rates[3].rate = MMRC_MCS_UNUSED;
	} else if (tb->caps.max_rates == 3) {
		out->rates[0] = (is_lookaround) ? lookaround0 : tb->best_tp;
		out->rates[1] = (is_lookaround) ? lookaround1 : tb->second_tp;
		out->rates[2] = tb->best_prob;
		out->rates[3].rate = MMRC_MCS_UNUSED;
	} else {
		out->rates[0] = (is_lookaround) ? lookaround0 : tb->best_tp;
		out->rates[1] = (is_lookaround) ? lookaround1 : tb->second_tp;
		out->rates[2] = tb->best_prob;
		out->rates[3] = tb->baseline;
	}

	/* For fallback rates, set RTS/CTS */
	for (i = 1; i < MMRC_MAX_CHAIN_LENGTH; i++)
		out->rates[i].flags |= BIT(MMRC_FLAGS_CTS_RTS);

	/* Allocate initial attempts for rate */
	allocate_initial_attempts(out, &rem_time, size);

	/* Calculate and allocate remaining attempts */
	calculate_remaining_attempts(tb, out, &rem_time, size);

	/* Enforce limits on each attempts */
	for (i = 0; i < MMRC_MAX_CHAIN_LENGTH; i++) {
		if (out->rates[i].rate != MMRC_MCS_UNUSED) {
			out->rates[i].attempts =
				out->rates[i].attempts == 0 ?
					MMRC_ATTEMPTS_TO_BITFIELD(
						MMRC_MIN_CHAIN_ATTEMPTS) :
					out->rates[i].attempts;
			out->rates[i].attempts =
				out->rates[i].attempts >
						MMRC_MAX_CHAIN_ATTEMPTS ?
					MMRC_ATTEMPTS_TO_BITFIELD(
						MMRC_MAX_CHAIN_ATTEMPTS) :
					out->rates[i].attempts;
			if (i == lookaround_index &&
			    tb->lookaround_wrap != LOOKAROUND_RATE_INIT)
				out->rates[i].attempts =
					MMRC_ATTEMPTS_TO_BITFIELD(1);
		}
	}

	/*
	 * Give the best rate at least 2 attempts to keep peak throughput
	 * unless it is too low
	 */
	if (out->rates[best_index].attempts == 1 &&
	    out->rates[best_index].rate > MMRC_MCS1)
		out->rates[best_index].attempts = MMRC_ATTEMPTS_TO_BITFIELD(2);
	else if (out->rates[best_index].rate <= MMRC_MCS1)
		out->rates[best_index].attempts = 1;
}

static u32 calc_ewma_average(u32 avg, u32 latest, u32 weight)
{
	WARN_ON_ONCE(!(weight <= 100));

	if (avg == 0)
		return latest;

	return ((latest * (100 - weight)) + (avg * weight)) / 100;
}

static void mmrc_process_variation(struct mmrc_table *tb, u16 current_success,
				   u32 index)
{
	u32 current_variation;

	/*
	 * Only process probability variation for the best rate. It is likely
	 * the only rate to have enough data to see the variation and its
	 * statistics are more affected because they are usually collected over
	 * the full period.
	 */
	if (index != tb->best_tp.index)
		return;

	if (current_success == 0) {
		if (!tb->unconverged) {
			/*
			 * Best rate is failing completely, go to unconverged
			 * mode
			 */
			tb->unconverged = true;
			tb->newly_unconverged = true;
		}
		return;
	}

	if (tb->table[index].prob == 0)
		return;

	/* Don't process variation while converging after association */
	if (tb->lookaround_wrap == LOOKAROUND_RATE_INIT)
		return;

	current_variation = abs(current_success - tb->table[index].prob);

	/* Calculate the EWMA of the probability variation */
	tb->probability_variation = calc_ewma_average(
		tb->probability_variation, current_variation, VARIATION_EWMA);

	/*
	 * Process the variation direction to distinguish converged and
	 * unconverged scenarios
	 */
	if (tb->probability_variation >= MODERATE_VARIATION_THRESHOLD ||
	    tb->interference_likely) {
		if ((current_success - tb->table[index].prob) *
			    tb->probability_variation_direction <
		    0)
			tb->probability_variation_direction = 0;
		else if (current_success > tb->table[index].prob)
			tb->probability_variation_direction =
				min(tb->probability_variation_direction + 1,
				    MAX_VARIATION_DIRECTION);
		else if (current_success < tb->table[index].prob)
			tb->probability_variation_direction =
				max(tb->probability_variation_direction - 1,
				    -MAX_VARIATION_DIRECTION);
	}

	if (tb->best_rate_cycle_count > VARIATION_DIRECTION_THRESHOLD &&
	    tb->probability_variation >= SIGNIFICANT_VARIATION_THRESHOLD) {
		/*
		 * Only enter interference mode if the best rate is stable for
		 * enough cycles to determine the direction is random and not
		 * in one direction only
		 */
		if (abs(tb->probability_variation_direction) <=
			    VARIATION_DIRECTION_THRESHOLD &&
		    !tb->interference_likely) {
			tb->interference_likely = true;
		}
	} else if (tb->interference_likely &&
		   (tb->probability_variation <= MINOR_VARIATION_THRESHOLD ||
		    abs(tb->probability_variation_direction) ==
			    MAX_VARIATION_DIRECTION)) {
		/*
		 * Exit interference mode if the variability drops or the
		 * direction stops being random
		 */
		tb->interference_likely = false;
	}
}

void mmrc_update(struct mmrc_table *tb)
{
	u32 i;
	u16 this_success;
	u32 scale;
	u32 scaled_ewma;
	u32 new_stats = 0;
	u32 attempts_for_stats;
	u32 success_for_stats;
	u32 min_stats;
	u32 throughput;
	u32 evidence_sent;

	tb->cycle_cnt++;

	/* Allow less minimum stats when converging */
	if (tb->lookaround_wrap != LOOKAROUND_RATE_INIT)
		min_stats = STATS_MIN_NORMAL;
	else
		min_stats = STATS_MIN_INIT;

	for (i = 0; i < rows_from_sta_caps(&tb->caps); i++) {
		/* This algorithm is keeping track of the amount of evidence,
		 * being packets that have been recently sent at this rate.
		 * This value is smoothed with an EWMA function over time and
		 * used to update the probability of a rate succeeding
		 * dynamically. This method allows MMRC to react timely if a
		 * new rate is used that hasn't been used recently
		 */

		/* Necessary to prevent a divide by 0 */
		if (tb->table[i].evidence == 0)
			scale = 0;
		else
			scale = ((tb->table[i].evidence * 2) * 100) /
				((tb->table[i].sent * EVIDENCE_SCALE) +
				 tb->table[i].evidence);

		/* Restrict scale to appropriate values */
		if (scale > 100)
			scale = 100;

		scaled_ewma = scale * EWMA / 100;

		/*
		 * Only count new packets for evidence if we will process
		 * them
		 */
		evidence_sent =
			tb->table[i].sent >= min_stats ? tb->table[i].sent : 0;
		tb->table[i].evidence = calc_ewma_average(
			tb->table[i].evidence, evidence_sent * EVIDENCE_SCALE,
			scaled_ewma);

		if (tb->table[i].evidence > EVIDENCE_MAX)
			tb->table[i].evidence = EVIDENCE_MAX;

		/* Try to use statistics from acknowledged AMPDUs first */
		attempts_for_stats = tb->table[i].back_mpdu_success +
				     tb->table[i].back_mpdu_failure;
		success_for_stats = tb->table[i].back_mpdu_success;

		/*
		 * Use the full statistics if rates are not converged or there
		 * were no AMPDUs for this rate or the remaining attempts are
		 * less than half of what we have from AMPDUs.
		 */
		if (!tb->table[i].have_sent_ampdus || tb->unconverged ||
		    attempts_for_stats < AMPDU_STATS_MIN ||
		    (tb->table[i].sent - attempts_for_stats <
		     attempts_for_stats / 2)) {
			attempts_for_stats = tb->table[i].sent;
			success_for_stats = tb->table[i].sent_success;
		}

		if (attempts_for_stats >= min_stats ||
		    (attempts_for_stats > 0 && tb->table[i].prob > 0)) {
			new_stats = 1;
			this_success =
				(100 * success_for_stats) / attempts_for_stats;

			if (scaled_ewma)
				mmrc_process_variation(tb, this_success, i);

			tb->table[i].prob = calc_ewma_average(
				tb->table[i].prob, this_success, scaled_ewma);

			/* Clear our sent statistics and update totals */
			tb->table[i].total_sent += tb->table[i].sent;
			tb->table[i].sent = 0;

			tb->table[i].total_success += tb->table[i].sent_success;
			tb->table[i].sent_success = 0;

			tb->table[i].back_mpdu_failure = 0;
			tb->table[i].back_mpdu_success = 0;
			tb->table[i].have_sent_ampdus = false;
		}

		throughput = calculate_throughput(tb, i);
		if (tb->table[i].max_throughput < throughput)
			tb->table[i].max_throughput = throughput;

		/*
		 * Reset the running average windows if reached collector
		 * limits
		 */
		if (tb->table[i].sum_throughput > (0xFFFFFFFF - throughput)) {
			tb->table[i].sum_throughput /=
				tb->table[i].avg_throughput_counter;
			tb->table[i].avg_throughput_counter = 1;
		}
		/* Update the sum and counter so it will be possible later to
		 * calculate the running average throughput
		 */
		tb->table[i].sum_throughput += throughput;
		tb->table[i].avg_throughput_counter++;
	}

	generate_table_priority(tb, new_stats);

	/*
	 * Switch to faster lookaround mode if rates drop low at very low
	 * bandwidth or we are in unconverged mode. Switching at low bandwidth
	 * and rate is to help recover quickly from rates where we would need
	 * to fragment standard MTU size packets.
	 */
	if (tb->lookaround_wrap != LOOKAROUND_RATE_INIT &&
	    (tb->unconverged || (tb->best_tp.bw == MMRC_BW_1MHZ &&
				 tb->best_tp.rate <= MMRC_MCS2))) {
		tb->lookaround_cnt = 0;
		tb->lookaround_wrap = LOOKAROUND_RATE_INIT;
		tb->stability_cnt_threshold = STABILITY_CNT_THRESHOLD_INIT;
	}

	/*
	 * If it is unlikely we can do the lookaround attempts in two RC cycles
	 * choose a new rate
	 */
	if (tb->current_lookaround_rate_attempts <=
	    (LOOKAROUND_RATE_ATTEMPTS / 2))
		tb->current_lookaround_rate_attempts = LOOKAROUND_RATE_ATTEMPTS;
}

void mmrc_feedback(struct mmrc_table *tb, struct mmrc_rate_table *rates,
		   s32 retry_count, bool was_aggregated)
{
	s32 ind = retry_count;
	u32 i;

	for (i = 0; i < MMRC_MAX_CHAIN_LENGTH; i++) {
		rate_update_index(tb, &rates->rates[i]);
		tb->table[rates->rates[i].index].have_sent_ampdus |=
			was_aggregated;

		if ((s32)rates->rates[i].attempts < ind) {
			ind = ind - rates->rates[i].attempts;
			tb->table[rates->rates[i].index].sent +=
				rates->rates[i].attempts;
			if (was_aggregated) {
				tb->table[rates->rates[i].index]
					.back_mpdu_failure +=
					rates->rates[i].attempts;
			}
		} else {
			tb->table[rates->rates[i].index].sent += ind;
			tb->table[rates->rates[i].index].sent_success += 1;
			if (was_aggregated) {
				tb->table[rates->rates[i].index]
					.back_mpdu_success += 1;
				tb->table[rates->rates[i].index]
					.back_mpdu_failure +=
					ind > 1 ? ind - 1 : 0;
			}
			return;
		}
	}
}

/*
 * Chooses a reasonable starting rate based on range (gathered from
 * RSSI measurements) or bandwidth. Then fills out the 3 retry rates
 * so a full set of rates is available.
 */
static void mmrc_init_rates(struct mmrc_table *tb, s8 rssi)
{
	tb->best_tp.bw = MMRC_MAX_BW(tb->caps.bandwidth);
	if (tb->caps.sgi_per_bw & SGI_PER_BW(tb->best_tp.bw))
		tb->best_tp.guard = MMRC_GUARD_TO_BITFIELD(MMRC_GUARD_SHORT);
	else
		tb->best_tp.guard = MMRC_GUARD_TO_BITFIELD(MMRC_GUARD_LONG);
	tb->best_tp.rate = MMRC_RATE_TO_BITFIELD(MMRC_MCS0);

	if (rssi >= MMRC_SHORT_RANGE_RSSI_LIMIT)
		tb->best_tp.rate = MMRC_RATE_TO_BITFIELD(MMRC_MCS7);
	else if (rssi < MMRC_SHORT_RANGE_RSSI_LIMIT &&
		 rssi >= MMRC_MID_RANGE_RSSI_LIMIT)
		tb->best_tp.rate = MMRC_RATE_TO_BITFIELD(MMRC_MCS3);
	else if (tb->best_tp.bw == MMRC_BW_1MHZ ||
		 tb->best_tp.bw == MMRC_BW_2MHZ)
		/*
		 * To compensate for slow feedback when running with 1 and 2
		 * MHz bandwidth, we start from MCS3 which will correspond to
		 * reasonable feedback and will avoid resetting the rate table
		 * evidence.
		 */
		tb->best_tp.rate = MMRC_RATE_TO_BITFIELD(MMRC_MCS3);

	tb->best_tp.ss = MMRC_SS_TO_BITFIELD(MMRC_SPATIAL_STREAM_1);
	rate_update_index(tb, &tb->best_tp);
	/* Init every rate in case they are needed to set the retry rates */
	tb->second_tp = tb->best_tp;
	tb->best_prob = tb->best_tp;
	tb->baseline = tb->best_tp;
	mmrc_fill_retry_rates(tb);
}

void mmrc_sta_init(struct mmrc_table *tb, struct mmrc_sta_capabilities *caps,
		   s8 rssi)
{
	u32 i;
	u16 row_count = rows_from_sta_caps(caps);

	memset(tb, 0, mmrc_memory_required_for_caps(caps));
	memcpy(&tb->caps, caps, sizeof(tb->caps));

	for (i = 0; i < row_count; i++) {
		tb->table[i].prob = RATE_INIT_PROBABILITY;
		tb->table[i].evidence = 0;
		tb->table[i].sum_throughput = 0;
		tb->table[i].avg_throughput_counter = 0;
		tb->table[i].max_throughput = 0;
	}

	tb->fixed_rate.rate = MMRC_MCS_UNUSED;
	tb->cycle_cnt = 0;
	tb->last_lookaround_cycle = 0;
	tb->lookaround_cnt = 0;
	tb->lookaround_wrap = LOOKAROUND_RATE_INIT;
	tb->unconverged = true;
	tb->newly_unconverged = true;
	tb->stability_cnt_threshold = STABILITY_CNT_THRESHOLD_INIT;
	tb->baseline = get_rate_row(tb, find_baseline_index(tb));
	mmrc_init_rates(tb, rssi);
}

bool mmrc_set_fixed_rate(struct mmrc_table *tb, struct mmrc_rate fixed_rate)
{
	bool caps_support_rate = true;

	/* Do not accept rate which does not support the STA capabilities */
	if ((BIT(fixed_rate.rate) & tb->caps.rates) == 0 ||
	    (BIT(fixed_rate.bw) & tb->caps.bandwidth) == 0 ||
	    (BIT(fixed_rate.ss) & tb->caps.spatial_streams) == 0 ||
	    (BIT(fixed_rate.guard) & tb->caps.guard) == 0)
		caps_support_rate = false;

	if (validate_rate(tb, &fixed_rate) && caps_support_rate) {
		tb->fixed_rate = fixed_rate;
		rate_update_index(tb, &tb->fixed_rate);
		return true;
	}

	return false;
}