Re: ath10k firmware sends probes on DFS channels without radar detection

[Ben Greear <greearb@candelatech.com>]

On 12/15/2016 07:22 AM, Jean-Pierre Tosoni wrote:
> Jouni,
>
> Thanks for the suggestion, I already tried something like this in wmi.c,
> with the same result:
>
> - Before patching the firmware scans DFS channels actively (with probes).
>
> - After patching, the firmware scans DFS channels passively *until* any
> beacon is received on the DFS channel. When *any* beacon is seen, the
> firmware decides to scan actively on its own, without any new IR/RADAR
> info from the driver.
>
> So, your patch is required but not sufficient.
>
> Somehow I was able to overcome this by reloading the regulation domain
> in the radio card before each scan request:
>
> ////// awful patch ahead ////////
>
> --- a/drivers/net/wireless/ath/ath10k/mac.c
> +++ b/drivers/net/wireless/ath/ath10k/mac.c
> @@ -2842,7 +2842,9 @@ static int ath10k_update_channel_list(st
>   			ch->chan_radar =
>   				!!(channel->flags & IEEE80211_CHAN_RADAR);
>
> -			passive = channel->flags & IEEE80211_CHAN_NO_IR;
> +			passive = channel->flags & (IEEE80211_CHAN_NO_IR |
> +						    IEEE80211_CHAN_RADAR);

So, should we add a new flag in firmware and driver that means 'really-no-IR', or
should the NO_IR flag here just always make the firmware never do IR when probing
regardless of whether it has seen beacons or not?

Thanks,
Ben

> +
>   			ch->passive = passive;
>
>   			ch->freq = channel->center_freq;
> @@ -3548,6 +3550,9 @@ static int ath10k_start_scan(struct ath1
>
>   	lockdep_assert_held(&ar->conf_mutex);
>
> +	if (ar->state == ATH10K_STATE_ON)
> +		ath10k_regd_update(ar);
> +
>   	ret = ath10k_wmi_start_scan(ar, arg);
>   	if (ret)
>   		return ret;
>
> ////////////////////////////////////////
>
> ...But this sets a terrible penalty on performance when applied to
> background scan.
>
>
> On 12/14/16 20:58 Jouni Malinen wrote:
>>
>> On Tue, Dec 06, 2016 at 06:02:52PM +0100, Jean-Pierre Tosoni wrote:
>>> This follows on the previous discussion
>>> 	"Client station sends probes on DFS channels"
>>>
>>> Problem:
>>> The combination of QCA988X firmware v10.2.4.70-2 + ath10k +
>>> wpa_supplicant do not comply with the norm ETSI/EN 301-893 section
>>> 4.7; because they can send probes for 600s when no AP is around.
>>>
>>> Analysis:
>>> The problem seems to lie in the firmware, which regards the presence
>>> of *any* beacon as a proof that the channel is radar-clean for 600s.
>>
>> I don't think this is really firmware, but cfg80211 regulatory code and
>> how it interacts with ath10k..
>>
>>> - there is no obvious fix working in ath10k.
>>> - the issue does not show up with other mac80211 devices like ath9k.
>>> - wpa_supplicant considers this is a kernel issue [2]
>>
>> There seems to be a difference between ath9k (mac80211-based Probe Request
>> frame sending) and ath10k (firmware) in this area for active scanning.
>> mac80211 uses IEEE80211_CHAN_NO_IR | IEEE80211_CHAN_RADAR while ath10k
>> uses IEEE80211_CHAN_NO_IR. I'd assume this difference results in ath10k
>> using cfg80211 beacon hints (etc.) to update the NO_IR flag and that might
>> be behind the difference you see.
>>
>> Could you check whether the following change gets you the behavior you
>> want to see here? I have not had a chance to test this yet, but based on
>> code review, it looks like something that brings the same behavior to
>> ath10k that ath9k has for this through mac80211.
>>
>>
>> diff --git a/drivers/net/wireless/ath/ath10k/mac.c
>> b/drivers/net/wireless/ath/ath10k/mac.c
>> index aa545a1..758dbbd 100644
>> --- a/drivers/net/wireless/ath/ath10k/mac.c
>> +++ b/drivers/net/wireless/ath/ath10k/mac.c
>> @@ -2973,7 +2973,8 @@ static int ath10k_update_channel_list(struct ath10k
>> *ar)
>>   			ch->chan_radar =
>>   				!!(channel->flags & IEEE80211_CHAN_RADAR);
>>
>> -			passive = channel->flags & IEEE80211_CHAN_NO_IR;
>> +			passive = channel->flags & (IEEE80211_CHAN_NO_IR |
>> +						    IEEE80211_CHAN_RADAR);
>>   			ch->passive = passive;
>>
>>   			ch->freq = channel->center_freq;
>>
>> --
>> Jouni Malinen                                            PGP id EFC895FA
>>
>> _______________________________________________
>> ath10k mailing list
>> ath10k@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/ath10k
>


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com


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