Re: [PATCH 2.6.38] ath9k: remove support for the FIF_PROMISC_IN_BSS filter flag

["Luis R. Rodriguez" <lrodriguez@atheros.com>]

On Tue, Mar 08, 2011 at 05:15:41PM -0800, Felix Fietkau wrote:
> On 2011-03-09 2:07 AM, Ben Greear wrote:
> > On 03/08/2011 04:48 PM, Felix Fietkau wrote:
> >> The hardware rx filter flag triggered by FIF_PROMISC_IN_BSS is overly broad
> >> and covers even frames with PHY errors. When this flag is enabled, this message
> >> shows up frequently during scanning or hardware resets:
> >>
> >> ath: Could not stop RX, we could be confusing the DMA engine when we start RX up
> >>
> >> Since promiscuous mode is usually not particularly useful, yet enabled by
> >> default by bridging (either used normally in 4-addr mode, or with hacks
> >> for various virtualization software), we should sacrifice it for better
> >> reliability during normal operation.
> >>
> >> This patch leaves it enabled if there are active monitor mode interfaces, since
> >> it's very useful for debugging.
> >>
> >> Signed-off-by: Felix Fietkau<nbd@openwrt.org>
> >> Cc: stable@kernel.org
> >> ---
> >>   drivers/net/wireless/ath/ath9k/recv.c |    4 +---
> >>   1 files changed, 1 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/net/wireless/ath/ath9k/recv.c b/drivers/net/wireless/ath/ath9k/recv.c
> >> index cb559e3..a9c3f46 100644
> >> --- a/drivers/net/wireless/ath/ath9k/recv.c
> >> +++ b/drivers/net/wireless/ath/ath9k/recv.c
> >> @@ -413,9 +413,7 @@ u32 ath_calcrxfilter(struct ath_softc *sc)
> >>   	 * mode interface or when in monitor mode. AP mode does not need this
> >>   	 * since it receives all in-BSS frames anyway.
> >>   	 */
> >> -	if (((sc->sc_ah->opmode != NL80211_IFTYPE_AP)&&
> >> -	     (sc->rx.rxfilter&  FIF_PROMISC_IN_BSS)) ||
> >> -	    (sc->sc_ah->is_monitoring))
> >> +	if (sc->sc_ah->is_monitoring)
> >>   		rfilt |= ATH9K_RX_FILTER_PROM;
> >>
> >>   	if (sc->rx.rxfilter&  FIF_CONTROL)
> > 
> > Should we enable this flag if we have multiple STA
> > interfaces?  I had to add something to ath5k recently
> > to put it into promisc to properly handle multiple STAs
> > associated with different APs, for instance.
> No, multiple interfaces is handled by the BSSID mask.
> 
> > Do you have any idea *why* enabling this flag causes the DMA error
> > messages?
> I don't know why exactly it happens, but it probably cannot be explained
> without going to the details of the inner workings of the MAC/baseband
> interaction. But as I mentioned in the description, this flag is overly
> broad and doesn't just bypass the address match, but lets all kinds of
> other crap through as well - in many situations where even 'normal'
> promiscuous behavior would be completely useless.
> I think because of that, disabling it for non-monitor operation is the
> right thing to do.

Nice find, thanks for looking at this. Are we cured now from all of
these rants? Or has anyone seem more?

  Luis