2016-02-01 09:41:25

by Jouni Malinen

Subject: [PATCH] mac80211: Interoperability workaround for 80+80 and 160 MHz channels

Number of deployed 80 MHz capable VHT stations that do not support 80+80
and 160 MHz bandwidths seem to misbehave when trying to connect to an AP
that advertises 80+80 or 160 MHz channel bandwidth in the VHT Operation
element. To avoid such issues with deployed devices, modify the design
based on recently accepted IEEE 802.11 standard changes (*).

This allows poorly implemented VHT 80 MHz stations to connect with the
AP in 80 MHz mode. 80+80 and 160 MHz capable stations need to support
the new workaround mechanism to allow full bandwidth to be used.
However, there are more or less no impacted station with 80+80/160
capability deployed.

The rebased version of this patch is based on the updated version from
Johannes Berg to take the HT/VHT chandef refactoring into account.

(*) Changes in
https://mentor.ieee.org/802.11/dcn/15/11-15-1530-04-000m-vht160-operation-signaling-through-non-zero-ccfs1.docx
were accepted during the IEEE 802.11 January 2016 meeting.

Signed-off-by: Jouni Malinen <[email protected]>
---
net/mac80211/util.c | 31 +++++++++++++++++++++++++++++--
1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/net/mac80211/util.c b/net/mac80211/util.c
index fb90d9c..df1eca8 100644
--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c
@@ -2364,10 +2364,23 @@ u8 *ieee80211_ie_build_vht_oper(u8 *pos, struct ieee80211_sta_vht_cap *vht_cap,

switch (chandef->width) {
case NL80211_CHAN_WIDTH_160:
- vht_oper->chan_width = IEEE80211_VHT_CHANWIDTH_160MHZ;
+ /*
+ * Convert 160 MHz channel width to new style as interop
+ * workaround.
+ */
+ vht_oper->chan_width = IEEE80211_VHT_CHANWIDTH_80MHZ;
+ vht_oper->center_freq_seg2_idx = vht_oper->center_freq_seg1_idx;
+ if (chandef->chan->center_freq < chandef->center_freq1)
+ vht_oper->center_freq_seg1_idx -= 8;
+ else
+ vht_oper->center_freq_seg1_idx += 8;
break;
case NL80211_CHAN_WIDTH_80P80:
- vht_oper->chan_width = IEEE80211_VHT_CHANWIDTH_80P80MHZ;
+ /*
+ * Convert 80+80 MHz channel width to new style as interop
+ * workaround.
+ */
+ vht_oper->chan_width = IEEE80211_VHT_CHANWIDTH_80MHZ;
break;
case NL80211_CHAN_WIDTH_80:
vht_oper->chan_width = IEEE80211_VHT_CHANWIDTH_80MHZ;
@@ -2430,6 +2443,20 @@ bool ieee80211_chandef_vht_oper(const struct ieee80211_vht_operation *oper,
case IEEE80211_VHT_CHANWIDTH_80MHZ:
new.width = NL80211_CHAN_WIDTH_80;
new.center_freq1 = cf1;
+ /* If needed, adjust based on the newer interop workaround. */
+ if (oper->center_freq_seg2_idx) {
+ unsigned int diff;
+
+ diff = abs(oper->center_freq_seg2_idx -
+ oper->center_freq_seg1_idx);
+ if (diff == 8) {
+ new.width = NL80211_CHAN_WIDTH_160;
+ new.center_freq1 = cf2;
+ } else if (diff > 8) {
+ new.width = NL80211_CHAN_WIDTH_80P80;
+ new.center_freq2 = cf2;
+ }
+ }
break;
case IEEE80211_VHT_CHANWIDTH_160MHZ:
new.width = NL80211_CHAN_WIDTH_160;
--
1.9.1

2016-02-02 15:13:31

by Johannes Berg

Subject: Re: [PATCH] mac80211: Interoperability workaround for 80+80 and 160 MHz channels

On Mon, 2016-02-01 at 11:40 +0200, Jouni Malinen wrote:
> Number of deployed 80 MHz capable VHT stations that do not support
> 80+80
> and 160 MHz bandwidths seem to misbehave when trying to connect to an
> AP
> that advertises 80+80 or 160 MHz channel bandwidth in the VHT
> Operation
> element. To avoid such issues with deployed devices, modify the
> design
> based on recently accepted IEEE 802.11 standard changes (*).
>
> This allows poorly implemented VHT 80 MHz stations to connect with
> the
> AP in 80 MHz mode. 80+80 and 160 MHz capable stations need to support
> the new workaround mechanism to allow full bandwidth to be used.
> However, there are more or less no impacted station with 80+80/160
> capability deployed.
>
> The rebased version of this patch is based on the updated version
> from
> Johannes Berg to take the HT/VHT chandef refactoring into account.
>
Applied.

johannes