Fix slow 5GHz WiFi detection on Arch Linux with MediaTek MT7921/MT7922

gistfile0.txt

# Fix: Slow 5GHz WiFi Detection on Arch Linux (MediaTek MT7921/MT7922)

## Problem

After booting, the 5GHz WiFi network takes a long time to appear while 2.4GHz shows up immediately.

## Cause

The wireless regulatory domain is set to `00` (world/unset), which forces **passive scanning** on 5GHz bands. This means the adapter must wait for beacon frames instead of actively probing for networks.

You can check with:
```bash
iw reg get
```

If you see `country 00: DFS-UNSET` with `PASSIVE-SCAN` on 5GHz frequencies, this is your issue.

## Solution

### 1. Install the regulatory database

```bash
sudo pacman -S wireless-regdb
```

### 2. Set your country code in the regdom config

Edit `/etc/conf.d/wireless-regdom` and uncomment your country (e.g., `BR` for Brazil):

```bash
sudo sed -i 's/^#WIRELESS_REGDOM="BR"/WIRELESS_REGDOM="BR"/' /etc/conf.d/wireless-regdom
```

### 3. Create modprobe config for early boot

```bash
echo 'options cfg80211 ieee80211_regdom=BR' | sudo tee /etc/modprobe.d/wireless-regdom.conf
```

### 4. (Optional) Disable ASPM for MT7921 latency fix

```bash
echo 'options mt7921e disable_aspm=1' | sudo tee -a /etc/modprobe.d/wireless-regdom.conf
```

### 5. Regenerate initramfs

```bash
sudo mkinitcpio -P
```

### 6. Reboot

After reboot, verify with:
```bash
iw reg get | head -5
```

You should see your country code (e.g., `country BR: DFS-FCC`) instead of `country 00`.

## Notes

- Replace `BR` with your [ISO 3166-1 alpha-2 country code](https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2)
- When connected to WiFi, the access point may override your regulatory domain via beacon hints (this is expected kernel behavior)
- The ASPM fix helps with general MT7921/MT7922 latency issues

## References

- https://bbs.archlinux.org/viewtopic.php?id=279356
- https://bbs.archlinux.org/viewtopic.php?id=287846