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Fix a corner case in RXEOL handling which was likely introduced by yours

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truly.

Before 802.11n, the RX descriptor list would employ the "self-linked tail
descriptor" trick which linked the last descriptor back to itself.
This way, the RX engine would never hit the "end" of the list and stop
processing RX (and assert RXEOL) as it never hit a descriptor whose next
pointer was 0. It would just keep overwriting the last descriptor until
the software freed up some more RX descriptors and chained them onto the
end.

For 802.11n, this needs to stop as a self-linked RX descriptor tickles the
block-ack logic into ACK'ing whatever frames are received into that
self-linked descriptor - so in very busy periods, you could end up with
A-MPDU traffic that is ACKed but never received by the 802.11 stack.
This would cause some confusion as the ADDBA windows would suddenly
be out of sync.

So when that occured here, the last descriptor would be hit and the PCU
logic would stop. It would only start again when the RX descriptor list
was updated and the PCU RX engine was re-tickled. That wasn't being done,
so RXEOL would be continuously asserted and no RX would continue.

This patch introduces a new flag - sc->sc_kickpcu - which when set,
signals the RX task to kick the PCU after its processed whatever packets
it can. This way completed packets aren't discarded.

In case some other task gets called which resets the hardware, don't
update sc->sc_imask - instead, just update the hardware interrupt mask
directly and let either ath_rx_proc() or ath_reset() restore the imask
to its former setting.

Note: this bug was only triggered when doing a whole lot of frame snooping
with serial console IO in the RX task. This would defer interrupt processing
enough to cause an RX descriptor overflow. It doesn't happen in normal
conditions.

Approved by: re (kib, blanket)
This commit is contained in:
Adrian Chadd 2011-08-02 02:46:03 +00:00
parent 12eab787f3
commit 1fdadc0fb6
2 changed files with 36 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

36
sys/dev/ath/if_ath.c
View File

@ -1389,6 +1389,7 @@ ath_intr(void *arg)
}
}
if (status & HAL_INT_RXEOL) {
int imask = sc->sc_imask;
/*
* NB: the hardware should re-read the link when
* RXE bit is written, but it doesn't work at
@ -1398,10 +1399,22 @@ ath_intr(void *arg)
/*
* Disable RXEOL/RXORN - prevent an interrupt
* storm until the PCU logic can be reset.
* In case the interface is reset some other
* way before "sc_kickpcu" is called, don't
* modify sc_imask - that way if it is reset
* by a call to ath_reset() somehow, the
* interrupt mask will be correctly reprogrammed.
*/
sc->sc_imask &= ~(HAL_INT_RXEOL | HAL_INT_RXORN);
ath_hal_intrset(ah, sc->sc_imask);
imask &= ~(HAL_INT_RXEOL | HAL_INT_RXORN);
ath_hal_intrset(ah, imask);
/*
* Enqueue an RX proc, to handled whatever
* is in the RX queue.
* This will then kick the PCU.
*/
taskqueue_enqueue(sc->sc_tq, &sc->sc_rxtask);
sc->sc_rxlink = NULL;
sc->sc_kickpcu = 1;
}
if (status & HAL_INT_TXURN) {
sc->sc_stats.ast_txurn++;
@ -3776,6 +3789,25 @@ rx_next:
if (ath_dfs_tasklet_needed(sc, sc->sc_curchan))
taskqueue_enqueue(sc->sc_tq, &sc->sc_dfstask);
/*
* Now that all the RX frames were handled that
* need to be handled, kick the PCU if there's
* been an RXEOL condition.
*/
if (sc->sc_kickpcu) {
sc->sc_kickpcu = 0;
ath_stoprecv(sc);
sc->sc_imask |= (HAL_INT_RXEOL | HAL_INT_RXORN);
if (ath_startrecv(sc) != 0) {
if_printf(ifp,
"%s: couldn't restart RX after RXEOL; resetting\n",
__func__);
ath_reset(ifp);
return;
}
ath_hal_intrset(ah, sc->sc_imask);
}
if ((ifp->if_drv_flags & IFF_DRV_OACTIVE) == 0) {
#ifdef IEEE80211_SUPPORT_SUPERG
ieee80211_ff_age_all(ic, 100);

3
sys/dev/ath/if_athvar.h
View File

@ -254,7 +254,8 @@ struct ath_softc {
sc_tdma : 1,/* TDMA in use */
sc_setcca : 1,/* set/clr CCA with TDMA */
sc_resetcal : 1,/* reset cal state next trip */
sc_rxslink : 1;/* do self-linked final descriptor */
sc_rxslink : 1,/* do self-linked final descriptor */
sc_kickpcu : 1;/* kick PCU RX on next RX proc */
uint32_t sc_eerd; /* regdomain from EEPROM */
uint32_t sc_eecc; /* country code from EEPROM */
/* rate tables */