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Date:      Tue, 31 Jul 2012 23:47:15 GMT
From:      Adrian Chadd <adrian@FreeBSD.org>
To:        freebsd-gnats-submit@FreeBSD.org
Subject:   misc/170302: [ath] 802.11n frames are not being transmitted with multiple rates
Message-ID:  <201207312347.q6VNlFV6097444@red.freebsd.org>
Resent-Message-ID: <201207312350.q6VNo9kb003709@freefall.freebsd.org>

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>Number:         170302
>Category:       misc
>Synopsis:       [ath] 802.11n frames are not being transmitted with multiple rates
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Jul 31 23:50:09 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator:     Adrian Chadd
>Release:        9.0-STABLE i386, with -HEAD net80211/ath
>Organization:
>Environment:
FreeBSD marilyn 9.0-STABLE FreeBSD 9.0-STABLE #6 r238210M: Sat Jul 21 16:59:42 PDT 2012     adrian@marilyn:/home/adrian/work/freebsd/stable/9/sys/i386/compile/MARILYN-9-STABLE  i386

>Description:
When doing some debugging, I noticed that the rate control code is not transmitting frames with multiple rate retries.

For example, with 'sysctl dev.ath.0.debug=2' set (TX descriptor debugging):


Q1[  0] (DS.V:0xea739000 DS.P:0x1d29c000) L:00000000 D:3958d82c F:0005
        Seq: 1904 swtry: 0 ADDBAW?: 0 DOBAW?: 0
        417f0242 00008240 00048000 0000008f 0000803a 00000000
        00000000 0090000f 00000000 3f000000 3f000000 3f000000 0080292c 00000101
        4ccfdabf ffffffff ffffffff 2d80282a 80808080 80808080 80808080 0000056b
  [end]
Q1[  0] (DS.V:0xea739000 DS.P:0x1d29c000) L:00000000 D:3958d82c F:0005 *
        Seq: 1904 swtry: 0 ADDBAW?: 0 DOBAW?: 0
        417f0242 00008240 00048000 0000008f 0000803a 00000000
        00000000 0090000f 00000000 3f000000 3f000000 3f000000 0080292c 00000101
        4ccfdabf ffffffff ffffffff 2d80282a 80808080 80808080 80808080 0000056b
  [end]

. descriptor field 3 is 0x8f, which shows only one 11n rate (rate attempt #0) is set.

>How-To-Repeat:
associate to an 802.11n AP.

>Fix:
The TX and rate control paths assume that if RTS/CTS is enabled, multi-rate retry should be disabled.

This is because of a limitation with the pre-11n chips - the AR5212 supports multi-rate retry but not with RTS/CTS enabled.


>Release-Note:
>Audit-Trail:
>Unformatted:



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