[FS#181] Changing TX power doesn't nothing (MediaTek MT7628AN ver:1 eco:2)

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FS#181 - Changing TX power doesn't nothing (MediaTek MT7628AN ver:1 eco:2)
User who did this - d.souza (dsouza)

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I can confirm this issue also with the 5Ghz radio on a TP-Link Archer C6 3.2 with both AN and AC network (MT7621 + MT7603EN 2.4Ghz + MT7613BEN 5Ghz) running a snapshot build (r17525-a46fa5c3a7).

The issue seems to be with the M76 driver which is completely ignoring the "TX Power" set via LuCI and UCI. I am saying the issue seems to be the Wi-Fi driver because UCI and iwinfo everything seems to be OK.

See the example below. I've set the TX Power to 0dbm for testing purposes, and UCI and iwinfo correctly show the value I've configured:

root at ap2:~# uci show wireless.radio1
wireless.radio1=wifi-device
wireless.radio1.type='mac80211'
wireless.radio1.path='1e140000.pcie/pci0000:00/0000:00:01.0/0000:02:00.0'
wireless.radio1.band='5g'
wireless.radio1.htmode='VHT80'
wireless.radio1.country='PA'
wireless.radio1.channel='100'
wireless.radio1.cell_density='0'
wireless.radio1.txpower='0'

root at ap2:~# iwinfo wlan1 info
wlan1     ESSID: "dshome5ghz-tst"
          Access Point: xx:xx:xx:xx:C8:40
          Mode: Master  Channel: 100 (5.500 GHz)
          Center Channel 1: 106 2: unknown
          Tx-Power: 0 dBm  Link Quality: 24/70
          Signal: -86 dBm  Noise: -92 dBm
          Bit Rate: 234.0 MBit/s
          Encryption: WPA2 PSK (CCMP)
          Type: nl80211  HW Mode(s): 802.11nac
          Hardware: 14C3:7663 14C3:7663 [MediaTek MT7613BE]
          TX power offset: none
          Frequency offset: none
          Supports VAPs: yes  PHY name: phy1
root at ap2:~#
**However the 0dBm configuration above has no effect on TX Power at all.**

With TX Power configured at 0 dBm for the 5Ghz radio in the example above, Wi-Fi signal should be very weak and should work only on the same room and close to the access point.

However as seen below the signal strength measured with a laptop located about **10 meters away from the access point with a brick wall between the laptop and the access point and the wi-if signal strength is still strong.** This is the same level as if TX Power is at 22dBm (driver default level), so in fact the TX Power configuration is not working:

ubuntu at ubuntu:~$ iwconfig wlp2s0
wlp2s0    IEEE 802.11  ESSID:"dshome5ghz-tst"  
          Mode:Managed  Frequency:5.5 GHz  Access Point: xx:xx:xx:xx:C8:40   
          Bit Rate=26 Mb/s   Tx-Power=22 dBm   
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Power Management:on
          Link Quality=42/70  Signal level=-68 dBm  
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:30   Missed beacon:0

I've experimented other TX Power levels, and none configuration has any effect on OpenWRT TX Power. I am not sure if this is an OpenWRT bug or if it is in fact a MT76 driver issue to be reported upstream by OpenWRT devs.
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More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=181#comment10103

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