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

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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

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




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