svn commit: r242144 - head/sys/dev/ath

[Adrian Chadd]

Author: adrian
Date: Fri Oct 26 16:31:12 2012
New Revision: 242144
URL: http://svn.freebsd.org/changeset/base/242144

Log:
  Since it's not immediately obvious whether the current TX path handles
  fragment rate lookups correctly, add a comment describing exactly that.
  
  The assumption in the fragment duration code is the duration of the next
  fragment will match the rate used by the current fragment.  But I think
  a rate lookup is being done for _each_ fragment.  For older pre-sample
  rate control this would almost always be the case, but for sample
  it may be incorrect more often then correct.

Modified:
  head/sys/dev/ath/if_ath_tx.c

Modified: head/sys/dev/ath/if_ath_tx.c
==============================================================================
--- head/sys/dev/ath/if_ath_tx.c	Fri Oct 26 16:30:49 2012	(r242143)
+++ head/sys/dev/ath/if_ath_tx.c	Fri Oct 26 16:31:12 2012	(r242144)
@@ -1067,6 +1067,10 @@ ath_tx_calc_duration(struct ath_softc *s
 			 * Include the size of next fragment so NAV is
 			 * updated properly.  The last fragment uses only
 			 * the ACK duration
+			 *
+			 * XXX TODO: ensure that the rate lookup for each
+			 * fragment is the same as the rate used by the
+			 * first fragment!
 			 */
 			dur += ath_hal_computetxtime(ah, rt,
 					bf->bf_m->m_nextpkt->m_pkthdr.len,