iwl4965: add comments to rate scaling code

Add comments to rate scaling code.

Signed-off-by: Ben Cahill <ben.m.cahill@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 409 insertions, 58 deletions

diff --git a/drivers/net/wireless/iwlwifi/iwl-4965-rs.c b/drivers/net/wireless/iwlwifi/iwl-4965-rs.c
index 8d3d9f72a8c..218c5a355dd 100644
--- a/drivers/net/wireless/iwlwifi/iwl-4965-rs.c
+++ b/drivers/net/wireless/iwlwifi/iwl-4965-rs.c
@@ -47,13 +47,12 @@
 #define IWL_NUMBER_TRY      1
 #define IWL_HT_NUMBER_TRY   3
 
-#define IWL_RATE_MAX_WINDOW		62
-#define IWL_RATE_HIGH_TH		10880
-#define IWL_RATE_MIN_FAILURE_TH		6
-#define IWL_RATE_MIN_SUCCESS_TH		8
-#define IWL_RATE_DECREASE_TH		1920
-#define IWL_RATE_INCREASE_TH            8960
-#define IWL_RATE_SCALE_FLUSH_INTVL   (2*HZ)        /*2 seconds */
+#define IWL_RATE_MAX_WINDOW		62	/* # tx in history window */
+#define IWL_RATE_MIN_FAILURE_TH		6	/* min failures to calc tpt */
+#define IWL_RATE_MIN_SUCCESS_TH		8	/* min successes to calc tpt */
+
+/* max time to accum history 2 seconds */
+#define IWL_RATE_SCALE_FLUSH_INTVL   (2*HZ)
 
 static u8 rs_ht_to_legacy[] = {
 	IWL_RATE_6M_INDEX, IWL_RATE_6M_INDEX,
@@ -69,54 +68,74 @@ struct iwl4965_rate {
 	u32 rate_n_flags;
 } __attribute__ ((packed));
 
+/**
+ * struct iwl4965_rate_scale_data -- tx success history for one rate
+ */
 struct iwl4965_rate_scale_data {
-	u64 data;
-	s32 success_counter;
-	s32 success_ratio;
-	s32 counter;
-	s32 average_tpt;
+	u64 data;		/* bitmap of successful frames */
+	s32 success_counter;	/* number of frames successful */
+	s32 success_ratio;	/* per-cent * 128  */
+	s32 counter;		/* number of frames attempted */
+	s32 average_tpt;	/* success ratio * expected throughput */
 	unsigned long stamp;
 };
 
+/**
+ * struct iwl4965_scale_tbl_info -- tx params and success history for all rates
+ *
+ * There are two of these in struct iwl_rate_scale_priv,
+ * one for "active", and one for "search".
+ */
 struct iwl4965_scale_tbl_info {
 	enum iwl4965_table_type lq_type;
 	enum iwl4965_antenna_type antenna_type;
-	u8 is_SGI;
-	u8 is_fat;
-	u8 is_dup;
-	u8 action;
-	s32 *expected_tpt;
-	struct iwl4965_rate current_rate;
-	struct iwl4965_rate_scale_data win[IWL_RATE_COUNT];
+	u8 is_SGI;	/* 1 = short guard interval */
+	u8 is_fat;	/* 1 = 40 MHz channel width */
+	u8 is_dup;	/* 1 = duplicated data streams */
+	u8 action;	/* change modulation; IWL_[LEGACY/SISO/MIMO]_SWITCH_* */
+	s32 *expected_tpt;	/* throughput metrics; expected_tpt_G, etc. */
+	struct iwl4965_rate current_rate;  /* rate_n_flags, uCode API format */
+	struct iwl4965_rate_scale_data win[IWL_RATE_COUNT]; /* rate histories */
 };
 
+/**
+ * struct iwl_rate_scale_priv -- driver's rate scaling private structure
+ *
+ * Pointer to this gets passed back and forth between driver and mac80211.
+ */
 struct iwl4965_rate_scale_priv {
-	u8 active_tbl;
-	u8 enable_counter;
-	u8 stay_in_tbl;
-	u8 search_better_tbl;
+	u8 active_tbl;		/* index of active table, range 0-1 */
+	u8 enable_counter;	/* indicates HT mode */
+	u8 stay_in_tbl;		/* 1: disallow, 0: allow search for new mode */
+	u8 search_better_tbl;	/* 1: currently trying alternate mode */
 	s32 last_tpt;
+
+	/* The following determine when to search for a new mode */
 	u32 table_count_limit;
-	u32 max_failure_limit;
-	u32 max_success_limit;
+	u32 max_failure_limit;	/* # failed frames before new search */
+	u32 max_success_limit;	/* # successful frames before new search */
 	u32 table_count;
-	u32 total_failed;
-	u32 total_success;
-	u32 flush_timer;
-	u8 action_counter;
+	u32 total_failed;	/* total failed frames, any/all rates */
+	u32 total_success;	/* total successful frames, any/all rates */
+	u32 flush_timer;	/* time staying in mode before new search */
+
+	u8 action_counter;	/* # mode-switch actions tried */
 	u8 antenna;
 	u8 valid_antenna;
 	u8 is_green;
 	u8 is_dup;
 	u8 phymode;
 	u8 ibss_sta_added;
+
+	/* The following are bitmaps of rates; IWL_RATE_6M_MASK, etc. */
 	u32 supp_rates;
 	u16 active_rate;
 	u16 active_siso_rate;
 	u16 active_mimo_rate;
 	u16 active_rate_basic;
+
 	struct iwl4965_link_quality_cmd lq;
-	struct iwl4965_scale_tbl_info lq_info[LQ_SIZE];
+	struct iwl4965_scale_tbl_info lq_info[LQ_SIZE]; /* "active", "search" */
 #ifdef CONFIG_MAC80211_DEBUGFS
 	struct dentry *rs_sta_dbgfs_scale_table_file;
 	struct dentry *rs_sta_dbgfs_stats_table_file;
@@ -142,6 +161,12 @@ static void rs_dbgfs_set_mcs(struct iwl4965_rate_scale_priv *rs_priv,
 				struct iwl4965_rate *mcs, int index)
 {}
 #endif
+
+/*
+ * Expected throughput metrics for following rates:
+ * 1, 2, 5.5, 11, 6, 9, 12, 18, 24, 36, 48, 54, 60 MBits
+ * "G" is the only table that supports CCK (the first 4 rates).
+ */
 static s32 expected_tpt_A[IWL_RATE_COUNT] = {
 	0, 0, 0, 0, 40, 57, 72, 98, 121, 154, 177, 186, 186
 };
@@ -244,6 +269,13 @@ static void rs_rate_scale_clear_window(struct iwl4965_rate_scale_data *window)
 	window->stamp = 0;
 }
 
+/**
+ * rs_collect_tx_data - Update the success/failure sliding window
+ *
+ * We keep a sliding window of the last 62 packets transmitted
+ * at this rate.  window->data contains the bitmask of successful
+ * packets.
+ */
 static int rs_collect_tx_data(struct iwl4965_rate_scale_data *windows,
 			      int scale_index, s32 tpt, u32 status)
 {
@@ -255,10 +287,18 @@ static int rs_collect_tx_data(struct iwl4965_rate_scale_data *windows,
 	if (scale_index < 0 || scale_index >= IWL_RATE_COUNT)
 		return -EINVAL;
 
+	/* Select data for current tx bit rate */
 	window = &(windows[scale_index]);
 
+	/*
+	 * Keep track of only the latest 62 tx frame attempts in this rate's
+	 * history window; anything older isn't really relevant any more.
+	 * If we have filled up the sliding window, drop the oldest attempt;
+	 * if the oldest attempt (highest bit in bitmap) shows "success",
+	 * subtract "1" from the success counter (this is the main reason
+	 * we keep these bitmaps!).
+	 */
 	if (window->counter >= win_size) {
-
 		window->counter = win_size - 1;
 		mask = 1;
 		mask = (mask << (win_size - 1));
@@ -268,7 +308,11 @@ static int rs_collect_tx_data(struct iwl4965_rate_scale_data *windows,
 		}
 	}
 
+	/* Increment frames-attempted counter */
 	window->counter = window->counter + 1;
+
+	/* Shift bitmap by one frame (throw away oldest history),
+	 * OR in "1", and increment "success" if this frame was successful. */
 	mask = window->data;
 	window->data = (mask << 1);
 	if (status != 0) {
@@ -276,6 +320,7 @@ static int rs_collect_tx_data(struct iwl4965_rate_scale_data *windows,
 		window->data |= 0x1;
 	}
 
+	/* Calculate current success ratio, avoid divide-by-0! */
 	if (window->counter > 0)
 		window->success_ratio = 128 * (100 * window->success_counter)
 					/ window->counter;
@@ -284,17 +329,22 @@ static int rs_collect_tx_data(struct iwl4965_rate_scale_data *windows,
 
 	fail_count = window->counter - window->success_counter;
 
+	/* Calculate average throughput, if we have enough history. */
 	if ((fail_count >= IWL_RATE_MIN_FAILURE_TH) ||
 	    (window->success_counter >= IWL_RATE_MIN_SUCCESS_TH))
 		window->average_tpt = (window->success_ratio * tpt + 64) / 128;
 	else
 		window->average_tpt = IWL_INVALID_VALUE;
 
+	/* Tag this window as having been updated */
 	window->stamp = jiffies;
 
 	return 0;
 }
 
+/*
+ * Fill uCode API rate_n_flags field, based on "search" or "active" table.
+ */
 static void rs_mcs_from_tbl(struct iwl4965_rate *mcs_rate,
 			   struct iwl4965_scale_tbl_info *tbl,
 			   int index, u8 use_green)
@@ -349,6 +399,10 @@ static void rs_mcs_from_tbl(struct iwl4965_rate *mcs_rate,
 	}
 }
 
+/*
+ * Interpret uCode API's rate_n_flags format,
+ * fill "search" or "active" tx mode table.
+ */
 static int rs_get_tbl_info_from_mcs(const struct iwl4965_rate *mcs_rate,
 				    int phymode, struct iwl4965_scale_tbl_info *tbl,
 				    int *rate_idx)
@@ -362,11 +416,12 @@ static int rs_get_tbl_info_from_mcs(const struct iwl4965_rate *mcs_rate,
 		*rate_idx = -1;
 		return -EINVAL;
 	}
-	tbl->is_SGI = 0;
+	tbl->is_SGI = 0;	/* default legacy setup */
 	tbl->is_fat = 0;
 	tbl->is_dup = 0;
-	tbl->antenna_type = ANT_BOTH;
+	tbl->antenna_type = ANT_BOTH;	/* default MIMO setup */
 
+	/* legacy rate format */
 	if (!(mcs_rate->rate_n_flags & RATE_MCS_HT_MSK)) {
 		ant_msk = (mcs_rate->rate_n_flags & RATE_MCS_ANT_AB_MSK);
 
@@ -386,6 +441,7 @@ static int rs_get_tbl_info_from_mcs(const struct iwl4965_rate *mcs_rate,
 		}
 		*rate_idx = index;
 
+	/* HT rate format, SISO (might be 20 MHz legacy or 40 MHz fat width) */
 	} else if (iwl4965_rate_get_rate(mcs_rate->rate_n_flags)
 					<= IWL_RATE_SISO_60M_PLCP) {
 		tbl->lq_type = LQ_SISO;
@@ -410,6 +466,8 @@ static int rs_get_tbl_info_from_mcs(const struct iwl4965_rate *mcs_rate,
 			tbl->is_dup = 1;
 
 		*rate_idx = index;
+
+	/* HT rate format, MIMO (might be 20 MHz legacy or 40 MHz fat width) */
 	} else {
 		tbl->lq_type = LQ_MIMO;
 		if (mcs_rate->rate_n_flags & RATE_MCS_SGI_MSK)
@@ -564,8 +622,9 @@ static void rs_get_lower_rate(struct iwl4965_rate_scale_priv *lq_data,
 
 	rs_get_supported_rates(lq_data, NULL, tbl->lq_type, &rate_mask);
 
-	/* mask with station rate restriction */
+	/* Mask with station rate restriction */
 	if (is_legacy(tbl->lq_type)) {
+		/* supp_rates has no CCK bits in A mode */
 		if (lq_data->phymode == (u8) MODE_IEEE80211A)
 			rate_mask  = (u16)(rate_mask &
 			   (lq_data->supp_rates << IWL_FIRST_OFDM_RATE));
@@ -573,7 +632,7 @@ static void rs_get_lower_rate(struct iwl4965_rate_scale_priv *lq_data,
 			rate_mask = (u16)(rate_mask & lq_data->supp_rates);
 	}
 
-	/* if we did switched from HT to legacy check current rate */
+	/* If we switched from HT to legacy, check current rate */
 	if (switch_to_legacy && (rate_mask & (1 << scale_index))) {
 		rs_mcs_from_tbl(mcs_rate, tbl, scale_index, is_green);
 		return;
@@ -588,6 +647,9 @@ static void rs_get_lower_rate(struct iwl4965_rate_scale_priv *lq_data,
 		rs_mcs_from_tbl(mcs_rate, tbl, scale_index, is_green);
 }
 
+/*
+ * mac80211 sends us Tx status
+ */
 static void rs_tx_status(void *priv_rate,
 			 struct net_device *dev,
 			 struct sk_buff *skb,
@@ -641,11 +703,14 @@ static void rs_tx_status(void *priv_rate,
 	table = &lq->lq;
 	active_index = lq->active_tbl;
 
+	/* Get mac80211 antenna info */
 	lq->antenna = (lq->valid_antenna & local->hw.conf.antenna_sel_tx);
 	if (!lq->antenna)
 		lq->antenna = lq->valid_antenna;
 
+	/* Ignore mac80211 antenna info for now */
 	lq->antenna = lq->valid_antenna;
+
 	curr_tbl = &(lq->lq_info[active_index]);
 	search_tbl = &(lq->lq_info[(1 - active_index)]);
 	window = (struct iwl4965_rate_scale_data *)
@@ -664,6 +729,14 @@ static void rs_tx_status(void *priv_rate,
 		return;
 	}
 
+	/*
+	 * Ignore this Tx frame response if its initial rate doesn't match
+	 * that of latest Link Quality command.  There may be stragglers
+	 * from a previous Link Quality command, but we're no longer interested
+	 * in those; they're either from the "active" mode while we're trying
+	 * to check "search" mode, or a prior "search" mode after we've moved
+	 * to a new "search" mode (which might become the new "active" mode).
+	 */
 	if (retries &&
 	    (tx_mcs.rate_n_flags !=
 				le32_to_cpu(table->rs_table[0].rate_n_flags))) {
@@ -674,12 +747,17 @@ static void rs_tx_status(void *priv_rate,
 		return;
 	}
 
+	/* Update frame history window with "failure" for each Tx retry. */
 	while (retries) {
+		/* Look up the rate and other info used for each tx attempt.
+		 * Each tx attempt steps one entry deeper in the rate table. */
 		tx_mcs.rate_n_flags =
 		    le32_to_cpu(table->rs_table[index].rate_n_flags);
 		rs_get_tbl_info_from_mcs(&tx_mcs, priv->phymode,
 					  &tbl_type, &rs_index);
 
+		/* If type matches "search" table,
+		 * add failure to "search" history */
 		if ((tbl_type.lq_type == search_tbl->lq_type) &&
 		    (tbl_type.antenna_type == search_tbl->antenna_type) &&
 		    (tbl_type.is_SGI == search_tbl->is_SGI)) {
@@ -687,8 +765,10 @@ static void rs_tx_status(void *priv_rate,
 				tpt = search_tbl->expected_tpt[rs_index];
 			else
 				tpt = 0;
-			rs_collect_tx_data(search_win,
-					    rs_index, tpt, 0);
+			rs_collect_tx_data(search_win, rs_index, tpt, 0);
+
+		/* Else if type matches "current/active" table,
+		 * add failure to "current/active" history */
 		} else if ((tbl_type.lq_type == curr_tbl->lq_type) &&
 			   (tbl_type.antenna_type == curr_tbl->antenna_type) &&
 			   (tbl_type.is_SGI == curr_tbl->is_SGI)) {
@@ -698,6 +778,9 @@ static void rs_tx_status(void *priv_rate,
 				tpt = 0;
 			rs_collect_tx_data(window, rs_index, tpt, 0);
 		}
+
+		/* If not searching for a new mode, increment failed counter
+		 * ... this helps determine when to start searching again */
 		if (lq->stay_in_tbl)
 			lq->total_failed++;
 		--retries;
@@ -705,6 +788,11 @@ static void rs_tx_status(void *priv_rate,
 
 	}
 
+	/*
+	 * Find (by rate) the history window to update with final Tx attempt;
+	 * if Tx was successful first try, use original rate,
+	 * else look up the rate that was, finally, successful.
+	 */
 	if (!tx_resp->retry_count)
 		tx_mcs.rate_n_flags = tx_resp->control.tx_rate;
 	else
@@ -714,11 +802,14 @@ static void rs_tx_status(void *priv_rate,
 	rs_get_tbl_info_from_mcs(&tx_mcs, priv->phymode,
 				  &tbl_type, &rs_index);
 
+	/* Update frame history window with "success" if Tx got ACKed ... */
 	if (tx_resp->flags & IEEE80211_TX_STATUS_ACK)
 		status = 1;
 	else
 		status = 0;
 
+	/* If type matches "search" table,
+	 * add final tx status to "search" history */
 	if ((tbl_type.lq_type == search_tbl->lq_type) &&
 	    (tbl_type.antenna_type == search_tbl->antenna_type) &&
 	    (tbl_type.is_SGI == search_tbl->is_SGI)) {
@@ -728,6 +819,9 @@ static void rs_tx_status(void *priv_rate,
 			tpt = 0;
 		rs_collect_tx_data(search_win,
 				    rs_index, tpt, status);
+
+	/* Else if type matches "current/active" table,
+	 * add final tx status to "current/active" history */
 	} else if ((tbl_type.lq_type == curr_tbl->lq_type) &&
 		   (tbl_type.antenna_type == curr_tbl->antenna_type) &&
 		   (tbl_type.is_SGI == curr_tbl->is_SGI)) {
@@ -738,6 +832,8 @@ static void rs_tx_status(void *priv_rate,
 		rs_collect_tx_data(window, rs_index, tpt, status);
 	}
 
+	/* If not searching for new mode, increment success/failed counter
+	 * ... these help determine when to start searching again */
 	if (lq->stay_in_tbl) {
 		if (status)
 			lq->total_success++;
@@ -745,6 +841,7 @@ static void rs_tx_status(void *priv_rate,
 			lq->total_failed++;
 	}
 
+	/* See if there's a better rate or modulation mode to try. */
 	rs_rate_scale_perform(priv, dev, hdr, sta);
 	sta_info_put(sta);
 	return;
@@ -774,11 +871,19 @@ static u8 rs_is_other_ant_connected(u8 valid_antenna,
 	return 0;
 }
 
+/*
+ * Begin a period of staying with a selected modulation mode.
+ * Set "stay_in_tbl" flag to prevent any mode switches.
+ * Set frame tx success limits according to legacy vs. high-throughput,
+ * and reset overall (spanning all rates) tx success history statistics.
+ * These control how long we stay using same modulation mode before
+ * searching for a new mode.
+ */
 static void rs_set_stay_in_table(u8 is_legacy,
 				 struct iwl4965_rate_scale_priv *lq_data)
 {
 	IWL_DEBUG_HT("we are staying in the same table\n");
-	lq_data->stay_in_tbl = 1;
+	lq_data->stay_in_tbl = 1;	/* only place this gets set */
 	if (is_legacy) {
 		lq_data->table_count_limit = IWL_LEGACY_TABLE_COUNT;
 		lq_data->max_failure_limit = IWL_LEGACY_FAILURE_LIMIT;
@@ -793,6 +898,9 @@ static void rs_set_stay_in_table(u8 is_legacy,
 	lq_data->total_success = 0;
 }
 
+/*
+ * Find correct throughput table for given mode of modulation
+ */
 static void rs_get_expected_tpt_table(struct iwl4965_rate_scale_priv *lq_data,
 				      struct iwl4965_scale_tbl_info *tbl)
 {
@@ -827,17 +935,33 @@ static void rs_get_expected_tpt_table(struct iwl4965_rate_scale_priv *lq_data,
 }
 
 #ifdef CONFIG_IWL4965_HT
+/*
+ * Find starting rate for new "search" high-throughput mode of modulation.
+ * Goal is to find lowest expected rate (under perfect conditions) that is
+ * above the current measured throughput of "active" mode, to give new mode
+ * a fair chance to prove itself without too many challenges.
+ *
+ * This gets called when transitioning to more aggressive modulation
+ * (i.e. legacy to SISO or MIMO, or SISO to MIMO), as well as less aggressive
+ * (i.e. MIMO to SISO).  When moving to MIMO, bit rate will typically need
+ * to decrease to match "active" throughput.  When moving from MIMO to SISO,
+ * bit rate will typically need to increase, but not if performance was bad.
+ */
 static s32 rs_get_best_rate(struct iwl4965_priv *priv,
 			    struct iwl4965_rate_scale_priv *lq_data,
-			    struct iwl4965_scale_tbl_info *tbl,
+			    struct iwl4965_scale_tbl_info *tbl,	/* "search" */
 			    u16 rate_mask, s8 index, s8 rate)
 {
+	/* "active" values */
 	struct iwl4965_scale_tbl_info *active_tbl =
 	    &(lq_data->lq_info[lq_data->active_tbl]);
-	s32 new_rate, high, low, start_hi;
 	s32 active_sr = active_tbl->win[index].success_ratio;
-	s32 *tpt_tbl = tbl->expected_tpt;
 	s32 active_tpt = active_tbl->expected_tpt[index];
+
+	/* expected "search" throughput */
+	s32 *tpt_tbl = tbl->expected_tpt;
+
+	s32 new_rate, high, low, start_hi;
 	u16 high_low;
 
 	new_rate = high = low = start_hi = IWL_RATE_INVALID;
@@ -848,6 +972,21 @@ static s32 rs_get_best_rate(struct iwl4965_priv *priv,
 		low = high_low & 0xff;
 		high = (high_low >> 8) & 0xff;
 
+		/*
+		 * Lower the "search" bit rate, to give new "search" mode
+		 * approximately the same throughput as "active" if:
+		 *
+		 * 1) "Active" mode has been working modestly well (but not
+		 *    great), and expected "search" throughput (under perfect
+		 *    conditions) at candidate rate is above the actual
+		 *    measured "active" throughput (but less than expected
+		 *    "active" throughput under perfect conditions).
+		 * OR
+		 * 2) "Active" mode has been working perfectly or very well
+		 *    and expected "search" throughput (under perfect
+		 *    conditions) at candidate rate is above expected
+		 *    "active" throughput (under perfect conditions).
+		 */
 		if ((((100 * tpt_tbl[rate]) > lq_data->last_tpt) &&
 		     ((active_sr > IWL_RATE_DECREASE_TH) &&
 		      (active_sr <= IWL_RATE_HIGH_TH) &&
@@ -855,21 +994,38 @@ static s32 rs_get_best_rate(struct iwl4965_priv *priv,
 		    ((active_sr >= IWL_RATE_SCALE_SWITCH) &&
 		     (tpt_tbl[rate] > active_tpt))) {
 
+			/* (2nd or later pass)
+			 * If we've already tried to raise the rate, and are
+			 * now trying to lower it, use the higher rate. */
 			if (start_hi != IWL_RATE_INVALID) {
 				new_rate = start_hi;
 				break;
 			}
+
 			new_rate = rate;
+
+			/* Loop again with lower rate */
 			if (low != IWL_RATE_INVALID)
 				rate = low;
+
+			/* Lower rate not available, use the original */
 			else
 				break;
+
+		/* Else try to raise the "search" rate to match "active" */
 		} else {
+			/* (2nd or later pass)
+			 * If we've already tried to lower the rate, and are
+			 * now trying to raise it, use the lower rate. */
 			if (new_rate != IWL_RATE_INVALID)
 				break;
+
+			/* Loop again with higher rate */
 			else if (high != IWL_RATE_INVALID) {
 				start_hi = high;
 				rate = high;
+
+			/* Higher rate not available, use the original */
 			} else {
 				new_rate = rate;
 				break;
@@ -886,6 +1042,9 @@ static inline u8 rs_is_both_ant_supp(u8 valid_antenna)
 	return (rs_is_ant_connected(valid_antenna, ANT_BOTH));
 }
 
+/*
+ * Set up search table for MIMO
+ */
 static int rs_switch_to_mimo(struct iwl4965_priv *priv,
 			     struct iwl4965_rate_scale_priv *lq_data,
 			     struct iwl4965_scale_tbl_info *tbl, int index)
@@ -906,6 +1065,7 @@ static int rs_switch_to_mimo(struct iwl4965_priv *priv,
 	if (priv->current_assoc_ht.tx_mimo_ps_mode == IWL_MIMO_PS_STATIC)
 		return -1;
 
+	/* Need both Tx chains/antennas to support MIMO */
 	if (!rs_is_both_ant_supp(lq_data->antenna))
 		return -1;
 
@@ -943,6 +1103,9 @@ static int rs_switch_to_mimo(struct iwl4965_priv *priv,
 #endif				/*CONFIG_IWL4965_HT */
 }
 
+/*
+ * Set up search table for SISO
+ */
 static int rs_switch_to_siso(struct iwl4965_priv *priv,
 			     struct iwl4965_rate_scale_priv *lq_data,
 			     struct iwl4965_scale_tbl_info *tbl, int index)
@@ -999,6 +1162,9 @@ static int rs_switch_to_siso(struct iwl4965_priv *priv,
 #endif				/*CONFIG_IWL4965_HT */
 }
 
+/*
+ * Try to switch to new modulation mode from legacy
+ */
 static int rs_move_legacy_other(struct iwl4965_priv *priv,
 				struct iwl4965_rate_scale_priv *lq_data,
 				int index)
@@ -1020,12 +1186,17 @@ static int rs_move_legacy_other(struct iwl4965_priv *priv,
 
 			search_tbl->lq_type = LQ_NONE;
 			lq_data->action_counter++;
+
+			/* Don't change antenna if success has been great */
 			if (window->success_ratio >= IWL_RS_GOOD_RATIO)
 				break;
+
+			/* Don't change antenna if other one is not connected */
 			if (!rs_is_other_ant_connected(lq_data->antenna,
 							tbl->antenna_type))
 				break;
 
+			/* Set up search table to try other antenna */
 			memcpy(search_tbl, tbl, sz);
 
 			rs_toggle_antenna(&(search_tbl->current_rate),
@@ -1036,6 +1207,8 @@ static int rs_move_legacy_other(struct iwl4965_priv *priv,
 
 		case IWL_LEGACY_SWITCH_SISO:
 			IWL_DEBUG_HT("LQ: Legacy switch to SISO\n");
+
+			/* Set up search table to try SISO */
 			memcpy(search_tbl, tbl, sz);
 			search_tbl->lq_type = LQ_SISO;
 			search_tbl->is_SGI = 0;
@@ -1051,6 +1224,8 @@ static int rs_move_legacy_other(struct iwl4965_priv *priv,
 			break;
 		case IWL_LEGACY_SWITCH_MIMO:
 			IWL_DEBUG_HT("LQ: Legacy switch MIMO\n");
+
+			/* Set up search table to try MIMO */
 			memcpy(search_tbl, tbl, sz);
 			search_tbl->lq_type = LQ_MIMO;
 			search_tbl->is_SGI = 0;
@@ -1083,6 +1258,9 @@ static int rs_move_legacy_other(struct iwl4965_priv *priv,
 
 }
 
+/*
+ * Try to switch to new modulation mode from SISO
+ */
 static int rs_move_siso_to_other(struct iwl4965_priv *priv,
 				 struct iwl4965_rate_scale_priv *lq_data,
 				 int index)
@@ -1173,6 +1351,9 @@ static int rs_move_siso_to_other(struct iwl4965_priv *priv,
 	return 0;
 }
 
+/*
+ * Try to switch to new modulation mode from MIMO
+ */
 static int rs_move_mimo_to_other(struct iwl4965_priv *priv,
 				 struct iwl4965_rate_scale_priv *lq_data,
 				 int index)
@@ -1193,6 +1374,8 @@ static int rs_move_mimo_to_other(struct iwl4965_priv *priv,
 		case IWL_MIMO_SWITCH_ANTENNA_A:
 		case IWL_MIMO_SWITCH_ANTENNA_B:
 			IWL_DEBUG_HT("LQ: MIMO SWITCH TO SISO\n");
+
+			/* Set up new search table for SISO */
 			memcpy(search_tbl, tbl, sz);
 			search_tbl->lq_type = LQ_SISO;
 			search_tbl->is_SGI = 0;
@@ -1212,6 +1395,8 @@ static int rs_move_mimo_to_other(struct iwl4965_priv *priv,
 
 		case IWL_MIMO_SWITCH_GI:
 			IWL_DEBUG_HT("LQ: MIMO SWITCH TO GI\n");
+
+			/* Set up new search table for MIMO */
 			memcpy(search_tbl, tbl, sz);
 			search_tbl->lq_type = LQ_MIMO;
 			search_tbl->antenna_type = ANT_BOTH;
@@ -1221,6 +1406,13 @@ static int rs_move_mimo_to_other(struct iwl4965_priv *priv,
 			else
 				search_tbl->is_SGI = 1;
 			lq_data->search_better_tbl = 1;
+
+			/*
+			 * If active table already uses the fastest possible
+			 * modulation (dual stream with short guard interval),
+			 * and it's working well, there's no need to look
+			 * for a better type of modulation!
+			 */
 			if ((tbl->lq_type == LQ_MIMO) &&
 			    (tbl->is_SGI)) {
 				s32 tpt = lq_data->last_tpt / 100;
@@ -1253,6 +1445,13 @@ static int rs_move_mimo_to_other(struct iwl4965_priv *priv,
 
 }
 
+/*
+ * Check whether we should continue using same modulation mode, or
+ * begin search for a new mode, based on:
+ * 1) # tx successes or failures while using this mode
+ * 2) # times calling this function
+ * 3) elapsed time in this mode (not used, for now)
+ */
 static void rs_stay_in_table(struct iwl4965_rate_scale_priv *lq_data)
 {
 	struct iwl4965_scale_tbl_info *tbl;
@@ -1264,15 +1463,27 @@ static void rs_stay_in_table(struct iwl4965_rate_scale_priv *lq_data)
 
 	tbl = &(lq_data->lq_info[active_tbl]);
 
+	/* If we've been disallowing search, see if we should now allow it */
 	if (lq_data->stay_in_tbl) {
 
+		/* Elapsed time using current modulation mode */
 		if (lq_data->flush_timer)
 			flush_interval_passed =
 			    time_after(jiffies,
 				       (unsigned long)(lq_data->flush_timer +
 					IWL_RATE_SCALE_FLUSH_INTVL));
 
+		/* For now, disable the elapsed time criterion */
 		flush_interval_passed = 0;
+
+		/*
+		 * Check if we should allow search for new modulation mode.
+		 * If many frames have failed or succeeded, or we've used
+		 * this same modulation for a long time, allow search, and
+		 * reset history stats that keep track of whether we should
+		 * allow a new search.  Also (below) reset all bitmaps and
+		 * stats in active history.
+		 */
 		if ((lq_data->total_failed > lq_data->max_failure_limit) ||
 		    (lq_data->total_success > lq_data->max_success_limit) ||
 		    ((!lq_data->search_better_tbl) && (lq_data->flush_timer)
@@ -1281,10 +1492,19 @@ static void rs_stay_in_table(struct iwl4965_rate_scale_priv *lq_data)
 				     lq_data->total_failed,
 				     lq_data->total_success,
 				     flush_interval_passed);
-			lq_data->stay_in_tbl = 0;
+
+			/* Allow search for new mode */
+			lq_data->stay_in_tbl = 0;	/* only place reset */
 			lq_data->total_failed = 0;
 			lq_data->total_success = 0;
 			lq_data->flush_timer = 0;
+
+		/*
+		 * Else if we've used this modulation mode enough repetitions
+		 * (regardless of elapsed time or success/failure), reset
+		 * history bitmaps and rate-specific stats for all rates in
+		 * active table.
+		 */
 		} else {
 			lq_data->table_count++;
 			if (lq_data->table_count >=
@@ -1298,6 +1518,9 @@ static void rs_stay_in_table(struct iwl4965_rate_scale_priv *lq_data)
 			}
 		}
 
+		/* If transitioning to allow "search", reset all history
+		 * bitmaps and stats in active table (this will become the new
+		 * "search" table). */
 		if (!lq_data->stay_in_tbl) {
 			for (i = 0; i < IWL_RATE_COUNT; i++)
 				rs_rate_scale_clear_window(&(tbl->win[i]));
@@ -1305,6 +1528,9 @@ static void rs_stay_in_table(struct iwl4965_rate_scale_priv *lq_data)
 	}
 }
 
+/*
+ * Do rate scaling and search for new modulation mode.
+ */
 static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 				  struct net_device *dev,
 				  struct ieee80211_hdr *hdr,
@@ -1350,6 +1576,11 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 	}
 	lq_data = (struct iwl4965_rate_scale_priv *)sta->rate_ctrl_priv;
 
+	/*
+	 * Select rate-scale / modulation-mode table to work with in
+	 * the rest of this function:  "search" if searching for better
+	 * modulation mode, or "active" if doing rate scaling within a mode.
+	 */
 	if (!lq_data->search_better_tbl)
 		active_tbl = lq_data->active_tbl;
 	else
@@ -1358,11 +1589,13 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 	tbl = &(lq_data->lq_info[active_tbl]);
 	is_green = lq_data->is_green;
 
+	/* current tx rate */
 	index = sta->last_txrate;
 
 	IWL_DEBUG_RATE("Rate scale index %d for type %d\n", index,
 		       tbl->lq_type);
 
+	/* rates available for this association, and for modulation mode */
 	rs_get_supported_rates(lq_data, hdr, tbl->lq_type,
 				&rate_mask);
 
@@ -1371,6 +1604,7 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 	/* mask with station rate restriction */
 	if (is_legacy(tbl->lq_type)) {
 		if (lq_data->phymode == (u8) MODE_IEEE80211A)
+			/* supp_rates has no CCK bits in A mode */
 			rate_scale_index_msk = (u16) (rate_mask &
 				(lq_data->supp_rates << IWL_FIRST_OFDM_RATE));
 		else
@@ -1383,11 +1617,13 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 	if (!rate_scale_index_msk)
 		rate_scale_index_msk = rate_mask;
 
+	/* If current rate is no longer supported on current association,
+	 * or user changed preferences for rates, find a new supported rate. */
 	if (index < 0 || !((1 << index) & rate_scale_index_msk)) {
 		index = IWL_INVALID_VALUE;
 		update_lq = 1;
 
-		/* get the lowest available rate */
+		/* get the highest available rate */
 		for (i = 0; i <= IWL_RATE_COUNT; i++) {
 			if ((1 << i) & rate_scale_index_msk)
 				index = i;
@@ -1399,11 +1635,19 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 		}
 	}
 
+	/* Get expected throughput table and history window for current rate */
 	if (!tbl->expected_tpt)
 		rs_get_expected_tpt_table(lq_data, tbl);
 
 	window = &(tbl->win[index]);
 
+	/*
+	 * If there is not enough history to calculate actual average
+	 * throughput, keep analyzing results of more tx frames, without
+	 * changing rate or mode (bypass most of the rest of this function).
+	 * Set up new rate table in uCode only if old rate is not supported
+	 * in current association (use new rate found above).
+	 */
 	fail_count = window->counter - window->success_counter;
 	if (((fail_count < IWL_RATE_MIN_FAILURE_TH) &&
 	     (window->success_counter < IWL_RATE_MIN_SUCCESS_TH))
@@ -1411,8 +1655,15 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 		IWL_DEBUG_RATE("LQ: still below TH succ %d total %d "
 			       "for index %d\n",
 			       window->success_counter, window->counter, index);
+
+		/* Can't calculate this yet; not enough history */
 		window->average_tpt = IWL_INVALID_VALUE;
+
+		/* Should we stay with this modulation mode,
+		 * or search for a new one? */
 		rs_stay_in_table(lq_data);
+
+		/* Set up new rate table in uCode, if needed */
 		if (update_lq) {
 			rs_mcs_from_tbl(&mcs_rate, tbl, index, is_green);
 			rs_fill_link_cmd(lq_data, &mcs_rate, &lq_data->lq);
@@ -1420,13 +1671,19 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 		}
 		goto out;
 
+	/* Else we have enough samples; calculate estimate of
+	 * actual average throughput */
 	} else
 		window->average_tpt = ((window->success_ratio *
 					tbl->expected_tpt[index] + 64) / 128);
 
+	/* If we are searching for better modulation mode, check success. */
 	if (lq_data->search_better_tbl) {
 		int success_limit = IWL_RATE_SCALE_SWITCH;
 
+		/* If good success, continue using the "search" mode;
+		 * no need to send new link quality command, since we're
+		 * continuing to use the setup that we've been trying. */
 		if ((window->success_ratio > success_limit) ||
 		    (window->average_tpt > lq_data->last_tpt)) {
 			if (!is_legacy(tbl->lq_type)) {
@@ -1438,55 +1695,78 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 					     lq_data->last_tpt);
 				lq_data->enable_counter = 1;
 			}
+			/* Swap tables; "search" becomes "active" */
 			lq_data->active_tbl = active_tbl;
 			current_tpt = window->average_tpt;
+
+		/* Else poor success; go back to mode in "active" table */
 		} else {
+			/* Nullify "search" table */
 			tbl->lq_type = LQ_NONE;
+
+			/* Revert to "active" table */
 			active_tbl = lq_data->active_tbl;
 			tbl = &(lq_data->lq_info[active_tbl]);
 
+			/* Revert to "active" rate and throughput info */
 			index = iwl4965_rate_index_from_plcp(
 				tbl->current_rate.rate_n_flags);
+			current_tpt = lq_data->last_tpt;
 
+			/* Need to set up a new rate table in uCode */
 			update_lq = 1;
-			current_tpt = lq_data->last_tpt;
 			IWL_DEBUG_HT("XXY GO BACK TO OLD TABLE\n");
 		}
+
+		/* Either way, we've made a decision; modulation mode
+		 * search is done, allow rate adjustment next time. */
 		lq_data->search_better_tbl = 0;
-		done_search = 1;
+		done_search = 1;	/* Don't switch modes below! */
 		goto lq_update;
 	}
 
+	/* (Else) not in search of better modulation mode, try for better
+	 * starting rate, while staying in this mode. */
 	high_low = rs_get_adjacent_rate(index, rate_scale_index_msk,
 					tbl->lq_type);
 	low = high_low & 0xff;
 	high = (high_low >> 8) & 0xff;
 
+	/* Collect measured throughputs for current and adjacent rates */
 	current_tpt = window->average_tpt;
-
 	if (low != IWL_RATE_INVALID)
 		low_tpt = tbl->win[low].average_tpt;
-
 	if (high != IWL_RATE_INVALID)
 		high_tpt = tbl->win[high].average_tpt;
 
-
+	/* Assume rate increase */
 	scale_action = 1;
 
+	/* Too many failures, decrease rate */
 	if ((window->success_ratio <= IWL_RATE_DECREASE_TH) ||
 	    (current_tpt == 0)) {
 		IWL_DEBUG_RATE("decrease rate because of low success_ratio\n");
 		scale_action = -1;
+
+	/* No throughput measured yet for adjacent rates; try increase. */
 	} else if ((low_tpt == IWL_INVALID_VALUE) &&
 		   (high_tpt == IWL_INVALID_VALUE))
 		scale_action = 1;
+
+	/* Both adjacent throughputs are measured, but neither one has better
+	 * throughput; we're using the best rate, don't change it! */
 	else if ((low_tpt != IWL_INVALID_VALUE) &&
 		 (high_tpt != IWL_INVALID_VALUE) &&
 		 (low_tpt < current_tpt) &&
 		 (high_tpt < current_tpt))
 		scale_action = 0;
+
+	/* At least one adjacent rate's throughput is measured,
+	 * and may have better performance. */
 	else {
+		/* Higher adjacent rate's throughput is measured */
 		if (high_tpt != IWL_INVALID_VALUE) {
+			/* Higher rate has better throughput */
 			if (high_tpt > current_tpt)
 				scale_action = 1;
 			else {
@@ -1494,7 +1774,10 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 				    ("decrease rate because of high tpt\n");
 				scale_action = -1;
 			}
+
+		/* Lower adjacent rate's throughput is measured */
 		} else if (low_tpt != IWL_INVALID_VALUE) {
+			/* Lower rate has better throughput */
 			if (low_tpt > current_tpt) {
 				IWL_DEBUG_RATE
 				    ("decrease rate because of low tpt\n");
@@ -1504,23 +1787,30 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 		}
 	}
 
+	/* Sanity check; asked for decrease, but success rate or throughput
+	 * has been good at old rate.  Don't change it. */
 	if (scale_action == -1) {
 		if ((low != IWL_RATE_INVALID) &&
 		    ((window->success_ratio > IWL_RATE_HIGH_TH) ||
 		     (current_tpt > (100 * tbl->expected_tpt[low]))))
 			scale_action = 0;
+
+	/* Sanity check; asked for increase, but success rate has not been great
+	 * even at old rate, higher rate will be worse.  Don't change it. */
 	} else if ((scale_action == 1) &&
 		   (window->success_ratio < IWL_RATE_INCREASE_TH))
 		scale_action = 0;
 
 	switch (scale_action) {
 	case -1:
+		/* Decrease starting rate, update uCode's rate table */
 		if (low != IWL_RATE_INVALID) {
 			update_lq = 1;
 			index = low;
 		}
 		break;
 	case 1:
+		/* Increase starting rate, update uCode's rate table */
 		if (high != IWL_RATE_INVALID) {
 			update_lq = 1;
 			index = high;
@@ -1528,6 +1818,7 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 
 		break;
 	case 0:
+		/* No change */
 	default:
 		break;
 	}
@@ -1537,16 +1828,28 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 		     index, scale_action, low, high, tbl->lq_type);
 
  lq_update:
+	/* Replace uCode's rate table for the destination station. */
 	if (update_lq) {
 		rs_mcs_from_tbl(&mcs_rate, tbl, index, is_green);
 		rs_fill_link_cmd(lq_data, &mcs_rate, &lq_data->lq);
 		rs_send_lq_cmd(priv, &lq_data->lq, CMD_ASYNC);
 	}
+
+	/* Should we stay with this modulation mode, or search for a new one? */
 	rs_stay_in_table(lq_data);
 
+	/*
+	 * Search for new modulation mode if we're:
+	 * 1)  Not changing rates right now
+	 * 2)  Not just finishing up a search
+	 * 3)  Allowing a new search
+	 */
 	if (!update_lq && !done_search && !lq_data->stay_in_tbl) {
+		/* Save current throughput to compare with "search" throughput*/
 		lq_data->last_tpt = current_tpt;
 
+		/* Select a new "search" modulation mode to try.
+		 * If one is found, set up the new "search" table. */
 		if (is_legacy(tbl->lq_type))
 			rs_move_legacy_other(priv, lq_data, index);
 		else if (is_siso(tbl->lq_type))
@@ -1554,11 +1857,14 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 		else
 			rs_move_mimo_to_other(priv, lq_data, index);
 
+		/* If new "search" mode was selected, set up in uCode table */
 		if (lq_data->search_better_tbl) {
+			/* Access the "search" table, clear its history. */
 			tbl = &(lq_data->lq_info[(1 - lq_data->active_tbl)]);
 			for (i = 0; i < IWL_RATE_COUNT; i++)
 				rs_rate_scale_clear_window(&(tbl->win[i]));
 
+			/* Use new "search" start rate */
 			index = iwl4965_rate_index_from_plcp(
 					tbl->current_rate.rate_n_flags);
 
@@ -1568,8 +1874,13 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 					 &lq_data->lq);
 			rs_send_lq_cmd(priv, &lq_data->lq, CMD_ASYNC);
 		}
-		tbl1 = &(lq_data->lq_info[lq_data->active_tbl]);
 
+		/* If the "active" (non-search) mode was legacy,
+		 * and we've tried switching antennas,
+		 * but we haven't been able to try HT modes (not available),
+		 * stay with best antenna legacy modulation for a while
+		 * before next round of mode comparisons. */
+		tbl1 = &(lq_data->lq_info[lq_data->active_tbl]);
 		if (is_legacy(tbl1->lq_type) &&
 #ifdef CONFIG_IWL4965_HT
 		    !priv->current_assoc_ht.is_ht &&
@@ -1580,9 +1891,13 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 			rs_set_stay_in_table(1, lq_data);
 		}
 
+		/* If we're in an HT mode, and all 3 mode switch actions
+		 * have been tried and compared, stay in this best modulation
+		 * mode for a while before next round of mode comparisons. */
 		if (lq_data->enable_counter &&
 		    (lq_data->action_counter >= IWL_ACTION_LIMIT)) {
 #ifdef CONFIG_IWL4965_HT_AGG
+			/* If appropriate, set up aggregation! */
 			if ((lq_data->last_tpt > TID_AGG_TPT_THREHOLD) &&
 			    (priv->lq_mngr.agg_ctrl.auto_agg)) {
 				priv->lq_mngr.agg_ctrl.tid_retry =
@@ -1593,6 +1908,14 @@ static void rs_rate_scale_perform(struct iwl4965_priv *priv,
 			lq_data->action_counter = 0;
 			rs_set_stay_in_table(0, lq_data);
 		}
+
+	/*
+	 * Else, don't search for a new modulation mode.
+	 * Put new timestamp in stay-in-modulation-mode flush timer if:
+	 * 1)  Not changing rates right now
+	 * 2)  Not just finishing up a search
+	 * 3)  flush timer is empty
+	 */
 	} else {
 		if ((!update_lq) && (!done_search) && (!lq_data->flush_timer))
 			lq_data->flush_timer = jiffies;
@@ -1789,15 +2112,14 @@ static void rs_rate_init(void *priv_rate, void *priv_sta,
 		priv->assoc_station_added = 1;
 	}
 
+	/* Find highest tx rate supported by hardware and destination station */
 	for (i = 0; i < mode->num_rates; i++) {
 		if ((sta->supp_rates & BIT(i)) &&
 		    (mode->rates[i].flags & IEEE80211_RATE_SUPPORTED))
 			sta->txrate = i;
 	}
 	sta->last_txrate = sta->txrate;
-	/* For MODE_IEEE80211A mode cck rate are at end
-	 * rate table
-	 */
+	/* For MODE_IEEE80211A, cck rates are at end of rate table */
 	if (local->hw.conf.phymode == MODE_IEEE80211A)
 		sta->last_txrate += IWL_FIRST_OFDM_RATE;
 
@@ -1810,11 +2132,16 @@ static void rs_rate_init(void *priv_rate, void *priv_sta,
 	crl->active_rate_basic = priv->active_rate_basic;
 	crl->phymode = priv->phymode;
 #ifdef CONFIG_IWL4965_HT
+	/*
+	 * active_siso_rate mask includes 9 MBits (bit 5), and CCK (bits 0-3),
+	 * supp_rates[] does not; shift to convert format, force 9 MBits off.
+	 */
 	crl->active_siso_rate = (priv->current_assoc_ht.supp_rates[0] << 1);
 	crl->active_siso_rate |= (priv->current_assoc_ht.supp_rates[0] & 0x1);
 	crl->active_siso_rate &= ~((u16)0x2);
 	crl->active_siso_rate = crl->active_siso_rate << IWL_FIRST_OFDM_RATE;
 
+	/* Same here */
 	crl->active_mimo_rate = (priv->current_assoc_ht.supp_rates[1] << 1);
 	crl->active_mimo_rate |= (priv->current_assoc_ht.supp_rates[1] & 0x1);
 	crl->active_mimo_rate &= ~((u16)0x2);
@@ -1844,11 +2171,14 @@ static void rs_fill_link_cmd(struct iwl4965_rate_scale_priv *lq_data,
 	struct iwl4965_rate new_rate;
 	struct iwl4965_scale_tbl_info tbl_type = { 0 };
 
+	/* Override starting rate (index 0) if needed for debug purposes */
 	rs_dbgfs_set_mcs(lq_data, tx_mcs, index);
 
+	/* Interpret rate_n_flags */
 	rs_get_tbl_info_from_mcs(tx_mcs, lq_data->phymode,
 				  &tbl_type, &rate_idx);
 
+	/* How many times should we repeat the initial rate? */
 	if (is_legacy(tbl_type.lq_type)) {
 		ant_toggle_count = 1;
 		repeat_rate = IWL_NUMBER_TRY;
@@ -1857,19 +2187,27 @@ static void rs_fill_link_cmd(struct iwl4965_rate_scale_priv *lq_data,
 
 	lq_cmd->general_params.mimo_delimiter =
 			is_mimo(tbl_type.lq_type) ? 1 : 0;
+
+	/* Fill 1st table entry (index 0) */
 	lq_cmd->rs_table[index].rate_n_flags =
 			cpu_to_le32(tx_mcs->rate_n_flags);
 	new_rate.rate_n_flags = tx_mcs->rate_n_flags;
 
 	if (is_mimo(tbl_type.lq_type) || (tbl_type.antenna_type == ANT_MAIN))
-		lq_cmd->general_params.single_stream_ant_msk = 1;
+		lq_cmd->general_params.single_stream_ant_msk
+			= LINK_QUAL_ANT_A_MSK;
 	else
-		lq_cmd->general_params.single_stream_ant_msk = 2;
+		lq_cmd->general_params.single_stream_ant_msk
+			= LINK_QUAL_ANT_B_MSK;
 
 	index++;
 	repeat_rate--;
 
+	/* Fill rest of rate table */
 	while (index < LINK_QUAL_MAX_RETRY_NUM) {
+		/* Repeat initial/next rate.
+		 * For legacy IWL_NUMBER_TRY == 1, this loop will not execute.
+		 * For HT IWL_HT_NUMBER_TRY == 3, this executes twice. */
 		while (repeat_rate > 0 && (index < LINK_QUAL_MAX_RETRY_NUM)) {
 			if (is_legacy(tbl_type.lq_type)) {
 				if (ant_toggle_count <
@@ -1881,7 +2219,10 @@ static void rs_fill_link_cmd(struct iwl4965_rate_scale_priv *lq_data,
 				}
 			}
 
+			/* Override next rate if needed for debug purposes */
 			rs_dbgfs_set_mcs(lq_data, &new_rate, index);
+
+			/* Fill next table entry */
 			lq_cmd->rs_table[index].rate_n_flags =
 					cpu_to_le32(new_rate.rate_n_flags);
 			repeat_rate--;
@@ -1891,12 +2232,17 @@ static void rs_fill_link_cmd(struct iwl4965_rate_scale_priv *lq_data,
 		rs_get_tbl_info_from_mcs(&new_rate, lq_data->phymode, &tbl_type,
 						&rate_idx);
 
+		/* Indicate to uCode which entries might be MIMO.
+		 * If initial rate was MIMO, this will finally end up
+		 * as (IWL_HT_NUMBER_TRY * 2), after 2nd pass, otherwise 0. */
 		if (is_mimo(tbl_type.lq_type))
 			lq_cmd->general_params.mimo_delimiter = index;
 
+		/* Get next rate */
 		rs_get_lower_rate(lq_data, &tbl_type, rate_idx,
 				  use_ht_possible, &new_rate);
 
+		/* How many times should we repeat the next rate? */
 		if (is_legacy(tbl_type.lq_type)) {
 			if (ant_toggle_count < NUM_TRY_BEFORE_ANTENNA_TOGGLE)
 				ant_toggle_count++;
@@ -1908,9 +2254,14 @@ static void rs_fill_link_cmd(struct iwl4965_rate_scale_priv *lq_data,
 		} else
 			repeat_rate = IWL_HT_NUMBER_TRY;
 
+		/* Don't allow HT rates after next pass.
+		 * rs_get_lower_rate() will change type to LQ_A or LQ_G. */
 		use_ht_possible = 0;
 
+		/* Override next rate if needed for debug purposes */
 		rs_dbgfs_set_mcs(lq_data, &new_rate, index);
+
+		/* Fill next table entry */
 		lq_cmd->rs_table[index].rate_n_flags =
 				cpu_to_le32(new_rate.rate_n_flags);
 
@@ -2006,9 +2357,9 @@ static ssize_t rs_sta_dbgfs_scale_table_write(struct file *file,
 	else
 		rs_priv->dbg_fixed.rate_n_flags = 0;
 
-	rs_priv->active_rate = 0x0FFF;
-	rs_priv->active_siso_rate = 0x1FD0;
-	rs_priv->active_mimo_rate = 0x1FD0;
+	rs_priv->active_rate = 0x0FFF;		/* 1 - 54 MBits, includes CCK */
+	rs_priv->active_siso_rate = 0x1FD0;	/* 6 - 60 MBits, no 9, no CCK */
+	rs_priv->active_mimo_rate = 0x1FD0;	/* 6 - 60 MBits, no 9, no CCK */
 
 	IWL_DEBUG_RATE("sta_id %d rate 0x%X\n",
 		rs_priv->lq.sta_id, rs_priv->dbg_fixed.rate_n_flags);
@@ -2209,7 +2560,7 @@ int iwl4965_fill_rs_info(struct ieee80211_hw *hw, char *buf, u8 sta_id)
 
 	/* Display the average rate of all samples taken.
 	 *
-	 * NOTE:  We multiple # of samples by 2 since the IEEE measurement
+	 * NOTE:  We multiply # of samples by 2 since the IEEE measurement
 	 * added from iwl4965_rates is actually 2X the rate */
 	if (samples)
 		count += sprintf(&buf[count],