[OpenWrt-Devel] Submitting PATCH for rtl8192cu HTmode deadlock

[Derek Werthmuller]

In reference to bug # 18539
https://dev.openwrt.org/ticket/18539#comment:4
The deadlock appears that when the adapter is in AP mode and client
negotiates into the HT modes.  I don't know if this effects the adapter
used in client modes.  But without the patch the adapter is not usable in
ap mode.  This adapter is integrated in the sunxi based bpi-r1 board.
I'd be interested in conversations to get this adapter up to some level of
802.11n HT mode.

The below patch I'd like to submit for evaluation for inclusion.
Cheers
   Derek


DEBUGing and patch done by sbrown
Comment (by sbrown):

 I found that the problem only occurs at HT rates.

 After looking at some more wireshark output, the problem seems to be
 that the aggregation sessions deadlock when a second one starts before
 the first one completes. That would explain why it only occurs in HT
 mode.

 The sequence on the air before the deadlock is:

 STA->AP block ack req
 STA->AP ping req
 AP->STA block ack resp
 AP->STA ping resp
 AP->STA block ack req
 STA->AP block ack resp

 The sequence on the air after the deadlock is:

 AP->STA block ack req
 STA->AP block ack req
 AP->STA block ack resp
 STA->AP block ack resp
 STA->AP ping req
 ...
 STA->AP ping req (repeats)

 If I disable aggregation in the driver with the attached patch, the
 problem goes away with a performance loss.

 {{{
  diff -rupN a/drivers/net/wireless/rtlwifi/rtl8192cu/sw.c
b/drivers/net/wireless/rtlwifi/rtl8192cu/sw.c
--- a/drivers/net/wireless/rtlwifi/rtl8192cu/sw.c    2015-04-03
07:10:19.343543253 -0400
+++ b/drivers/net/wireless/rtlwifi/rtl8192cu/sw.c    2015-04-03
07:11:51.323999358 -0400
@@ -59,7 +59,9 @@ static int rtl92cu_init_sw_vars(struct i
 {
     struct rtl_priv *rtlpriv = rtl_priv(hw);
     int err;
-
+ /* disable aggregation until the deadlock is fixed */
+        hw->flags &= ~IEEE80211_HW_AMPDU_AGGREGATION;
+
     rtlpriv->dm.dm_initialgain_enable = true;
     rtlpriv->dm.dm_flag = 0;
     rtlpriv->dm.disable_framebursting = false;

 }}}
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