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bes2600: scan-filter-5ghz: allow targeted single-channel scans (besser#1 follow-up)

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The original Patch I refused EVERY 5 GHz scan request unconditionally
(req->n_channels > 0 && band == NL80211_BAND_5GHZ).  This eliminated
the Pattern A storm but also broke 5 GHz association entirely:
NM / wpa_supplicant iterates a freq_list when a connection profile
specifies 802-11-wireless.band=a, issuing per-frequency single-channel
scans to find the BSS before associating.  Those single-channel scans
were also refused by our guard, so the BSS was never seen and
'Wi-Fi network could not be found' was the only outcome.

Tighten the guard: refuse only multi-channel 5 GHz scans (n_channels
> 1), which is the per-band-sweep pattern mac80211 issues internally
and the only one that triggers the firmware storm at the per-band
loop boundary.  Single-channel 5 GHz scans pass through to firmware,
which generally accepts them -- and when they happen to be rejected,
the failure is isolated and doesn't cascade.

Verified on ohm with pkgrel=3 (srcversion BEB625FA7443171EA8D55F7):
  - Pattern A count since boot: 0 (Phase 7 prediction still holds)
  - iw dev wlan0 scan freq 5180          -> allowed
  - iw dev wlan0 scan freq 5180 5200 ... -> refused -EOPNOTSUPP
  - NM 'nmcli connection up' with band=a -> associated to BSSID
    c0:25:06:e6:5b:33 on 5240 MHz / ch.48 in ~1 second
  - TX bitrate 150 Mbit/s MCS 7 40MHz short-GI (vs 72.2 Mbit/s
    HT20 on 2.4 GHz) -- ~2x throughput recovered

The change is a single byte (> 0 -> > 1) plus comment update; the
test confirmation above is what motivates it.

Refs: besser#1 (closed but tracked for follow-up like this), original
Patch I sha 093a503.
This commit is contained in:
Markus Fritsche
2026-05-18 15:56:34 +02:00
parent 093a5038b8
commit 8cd10f487c
1 changed files with 12 additions and 4 deletions
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bes2600/scan.c
+12 -4
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@@ -248,15 +248,23 @@ int bes2600_hw_scan(struct ieee80211_hw *hw,
* has req->channels[] from one band only (see ieee80211_prep_hw_scan
* in net/mac80211/scan.c). Refuse the 5 GHz iteration at the driver
* boundary so userspace gets a clean aborted-scan for that portion
* rather than waiting for the firmware reject to cascade up. 5 GHz
* band registration stays intact so direct-BSSID association to a
* known 5 GHz AP still works (no scan needed for that path).
* rather than waiting for the firmware reject to cascade up.
*
* Only the multi-channel case is refused (n_channels > 1): that's
* the per-band-sweep pattern mac80211 issues internally and the
* one that triggers the firmware storm at the per-band loop
* boundary. Single-channel 5 GHz scans (BSS verification, NM's
* per-freq iteration when 802-11-wireless.band=a is set) pass
* through to firmware, which generally accepts them since the
* storm is the back-to-back per-band issue, not a blanket 5 GHz
* reject. This preserves 5 GHz association via the
* "wpa_supplicant iterates freq_list per channel" path.
*
* Contract: per include/net/mac80211.h struct ieee80211_ops.hw_scan
* documentation, a negative return aborts the scan without requiring
* ieee80211_scan_completed().
*/
if (req->n_channels > 0 &&
if (req->n_channels > 1 &&
req->channels[0]->band == NL80211_BAND_5GHZ)
return -EOPNOTSUPP;