svn commit: r258031 - head/sys/dev/iwn

[Adrian Chadd]

Author: adrian
Date: Tue Nov 12 04:57:31 2013
New Revision: 258031
URL: http://svnweb.freebsd.org/changeset/base/258031

Log:
  Comment what 'mimo' does in the link quality table.

Modified:
  head/sys/dev/iwn/if_iwn.c

Modified: head/sys/dev/iwn/if_iwn.c
==============================================================================
--- head/sys/dev/iwn/if_iwn.c	Tue Nov 12 04:56:00 2013	(r258030)
+++ head/sys/dev/iwn/if_iwn.c	Tue Nov 12 04:57:31 2013	(r258031)
@@ -4368,7 +4368,17 @@ iwn_set_link_quality(struct iwn_softc *s
 		plcp = iwn_rate_to_plcp(sc, ni, rate);
 		linkq.retry[i] = plcp;
 
-		/* Special case for dual-stream rates? */
+		/*
+		 * The mimo field is an index into the table which
+		 * indicates the first index where it and subsequent entries
+		 * will not be using MIMO.
+		 *
+		 * Since we're filling linkq from 0..15 and we're filling
+		 * from the higest MCS rates to the lowest rates, if we
+		 * _are_ doing a dual-stream rate, set mimo to idx+1 (ie,
+		 * the next entry.)  That way if the next entry is a non-MIMO
+		 * entry, we're already pointing at it.
+		 */
 		if ((le32toh(plcp) & IWN_RFLAG_MCS) &&
 		    RV(le32toh(plcp)) > 7)
 			linkq.mimo = i + 1;