wifi: mt76: mt7915: disable VHT CAP SUPP CHAN WIDTH 160MHz for mt7915

[Anteus]

Fixes buggy 802.11ax on the RT3200 when connecting to some clients.

Partially reverts https://patchwork.kernel.org/project/linux-wireless/patch/20230301163739.52314-1-nbd@nbd.name/

Forum thread https://forum.openwrt.org/t/802-11ax-worse-than-802-11ac-with-mt76-driver/126466

[hnyman]

Forum link should be https://forum.openwrt.org/t/802-11ax-worse-than-802-11ac-with-mt76-driver/126466

(The original link here and in the commit message leads into wrong discussion)

[Anteus]

Whoops updated the comment.

[hnyman]

You should update (amend) also the commit message.
amend it and then git force push, so that the PR gets updated.

[Anteus]

Thanks it's updated as well. This needs testing I guess as how this affects 160MHz users on mt7915. But as this fixes 80MHz to perform as it should with some distance or objects in the way and 160MHz is not officially supported on mt7915 this should be preferred. I wonder what the root cause is though as it's a 160MHz setting, maybe something in the binary blobs?

[ThiloteE]

Will 160 MHz still work with this change?

[Anteus]

160 MHz seems to work on AX but is disabled on AC which uses VHT that this removes.

[Yorper]

Noticeable improvement on my e8450. This seriously needs merging for 23.05-rc2 to have a wider audience test and confirm.

[ThiloteE]

Came up in the forum. Mushoz's explanation:

There seems to be a lot of confusion about what the suggested patch [...] actually does.

It ONLY disables 160mhz AC mode. 160mhz AX mode is left untouched.

That means that if you want to stay within specification and run 80mhz mode on AX (or AC for that matter), you can, without running in the bug that is discussed in this thread.

Furthermore, if you want to push bandwidth as high as possible in 160mhz AX mode, you can as well. The ONLY thing that is disabled is 160mhz AC mode. AC 160mhz is such a niche case, that merging this patch feels like a no-brainer to me.

Both people that want to stay within spec will be happy, AND people that want to push the maximum amount of bandwidth will be happy.

[ThiloteE]

@Anteus have you also tested what happens, if you run the AP in ax 160 MHz mode and then an ac 160 MHz only client device tries to connect to it?

[Anteus]

@ThiloteE No I don't have any to test with.

[Yorper]

The chipset should really be set and running at the specifications outline by the manufacturer. Not pushing to do things they do not support, if that were the case we’d not be having this issue at all.

[NerdyProjects]

I think it is important to see this in 23.05 as many users have mediatek devices.
I can confirm that disabling VHT160 works. Netgear WAX206, Google Pixel 3a, 10m with some obstacles.

Stats after disabling VHT160 while upload was running: (Devices says RSSI of -66dBm)

Station c2:48:0a:fd:4b:8b (on wl1-ap4)
	inactive time:	0 ms
	rx bytes:	834983208
	rx packets:	552017
	tx bytes:	16871351
	tx packets:	254647
	tx retries:	0
	tx failed:	0
	rx drop misc:	3
	signal:  	-70 [-77, -78, -72, -77] dBm
	signal avg:	-70 [-77, -78, -72, -76] dBm
	tx bitrate:	612.5 MBit/s 80MHz HE-MCS 6 HE-NSS 2 HE-GI 1 HE-DCM 0
	tx duration:	16320175 us
	rx bitrate:	432.3 MBit/s 80MHz HE-MCS 4 HE-NSS 2 HE-GI 0 HE-DCM 0
	rx duration:	14315998 us
	last ack signal:-72 dBm
	avg ack signal:	-71 dBm
	airtime weight: 256
	authorized:	yes
	authenticated:	yes
	associated:	yes
	preamble:	long
	WMM/WME:	yes
	MFP:		no
	TDLS peer:	no
	DTIM period:	5
	beacon interval:100
	short slot time:yes

Iperf from wireless Pixel 6A to wired computer (upload test, first interval with VHT160 enabled):

Server listening on 5201 (test #2)
-----------------------------------------------------------
Accepted connection from 192.168.0.91, port 50358
[  5] local 192.168.0.121 port 5201 connected to 192.168.0.91 port 50372
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-1.00   sec  2.92 MBytes  24.5 Mbits/sec                  
[  5]   1.00-2.00   sec  1.76 MBytes  14.7 Mbits/sec                  
[  5]   2.00-3.00   sec  1.77 MBytes  14.9 Mbits/sec                  
[  5]   3.00-4.00   sec  1.92 MBytes  16.1 Mbits/sec                  
[  5]   3.00-4.00   sec  1.92 MBytes  16.1 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-4.00   sec  8.93 MBytes  18.7 Mbits/sec                  receiver
iperf3: the client has terminated
-----------------------------------------------------------
Server listening on 5201 (test #3)
-----------------------------------------------------------
Accepted connection from 192.168.0.143, port 51690
[  5] local 192.168.0.121 port 5201 connected to 192.168.0.143 port 51702
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-1.00   sec  43.3 MBytes   363 Mbits/sec                  
[  5]   1.00-2.00   sec  52.2 MBytes   438 Mbits/sec                  
[  5]   2.00-3.00   sec  50.4 MBytes   423 Mbits/sec                  
[  5]   3.00-4.00   sec  42.4 MBytes   356 Mbits/sec                  
[  5]   4.00-5.00   sec  38.6 MBytes   324 Mbits/sec                  
[  5]   5.00-6.00   sec  50.4 MBytes   422 Mbits/sec                  
[  5]   6.00-7.00   sec  52.4 MBytes   440 Mbits/sec                  
[  5]   7.00-8.00   sec  51.4 MBytes   431 Mbits/sec                  
[  5]   8.00-9.00   sec  47.4 MBytes   398 Mbits/sec                  
[  5]   9.00-10.00  sec  39.0 MBytes   327 Mbits/sec                  
[  5]  10.00-10.04  sec  1.45 MBytes   314 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-10.04  sec   469 MBytes   392 Mbits/sec                  receiver

I confirmed the fix by using the following snipped live patching the mac80211 script:

sed -i '/SHORT-GI-160/d;/vht160_hw/d;/$vht160/d;/# supported/d' /lib/netifd/wireless/mac80211.sh

from https://forum.openwrt.org/t/802-11ax-worse-than-802-11ac-with-mt76-driver/126466/578

[nbd168]

Please try latest OpenWrt master. In addition to removing the VHT160 capability, I also added a fix to hostapd for dealing with vht ext nss bw

[Anteus]

Thank you! It works great on 80MHz.