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

[Felix Fietkau <nbd@openwrt.org>]

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.

- Felix