fix(wifi): disable brcmfmac power save to prevent occasional drops (#8)

The brcmfmac driver (CM4 onboard WiFi) ships with power saving on; the
chip occasionally sleeps and fails to recover, requiring a manual
nmcli reconnect (verified on hardware: 'Power save: on', journal shows
'Couldn't initialize supplicant interface: Name owner lost').

Ship /etc/NetworkManager/conf.d/wifi-powersave-off.conf
(wifi.powersave=2) in the image so all connections have power save
disabled, and document the symptom/root cause/fix in MAINTAINING.

Author: fabiiw05

MAINTAINING.ja.md

@@ -203,6 +203,30 @@ timedatectl timesync-status   # ServerName=ntp.nict.jp / synced になれば OK
 systemd-networkd-wait-online` を実行し、上記 `timesyncd.conf.d` を配置しておけば、
 以降のイメージはこの問題を最初から回避できる。
 
+### WiFi 不安定（brcmfmac パワーセーブ）
+
+**症状**: WiFi が稀に切断される。`nmcli` で再接続すると復旧する。
+
+**原因**: `brcmfmac` ドライバ（CM4 内蔵 WiFi）のデフォルトで省電力
+モード（`Power save: on`）が有効になっており、省電力状態でチップが
+スリープに入り、復帰に失敗して再接続が必要になる。
+
+**対処（実機）**: NetworkManager でパワーセーブを恒久無効化する。
+
+```sh
+# 即時（再起動まで有効）
+sudo iw dev wlan0 set power_save off
+
+# 恒久（現在・将来の全接続に適用）
+sudo tee /etc/NetworkManager/conf.d/wifi-powersave-off.conf <<'EOF'
+[connection]
+wifi.powersave=2
+EOF
+```
+
+**イメージ側で根治済み**: `scripts/customize.sh` がビルド時に上記の
+設定ファイルを書き込むため、新規イメージでは最初から無効化されている。
+
 ## 今後の方向性
 
 - **カーネルの PKGBUILD 化**（ファイル注入をやめる）。pacman 管理下に入れば、

MAINTAINING.md

@@ -216,6 +216,30 @@ NetworkManager enablement, also run `systemctl disable systemd-networkd
 systemd-networkd.socket systemd-networkd-wait-online` and drop the
 `timesyncd.conf.d` file above, so future images avoid this out of the box.
 
+### WiFi instability (brcmfmac power save)
+
+**Symptom**: WiFi occasionally drops; reconnecting via `nmcli` restores it.
+
+**Root cause**: the `brcmfmac` driver (CM4 onboard WiFi) has power saving
+enabled by default (`Power save: on`). In this state the driver occasionally
+puts the chip to sleep and fails to recover, requiring a manual reconnect.
+
+**Fix (on device)**: disable power save permanently via NetworkManager.
+
+```sh
+# Immediate (until reboot)
+sudo iw dev wlan0 set power_save off
+
+# Permanent (applies to all connections, current and future)
+sudo tee /etc/NetworkManager/conf.d/wifi-powersave-off.conf <<'EOF'
+[connection]
+wifi.powersave=2
+EOF
+```
+
+**Fixed in the image**: `scripts/customize.sh` writes the config file above
+at build time, so fresh images ship with WiFi power saving disabled.
+
 ## Future directions
 
 - **Package the kernel as a PKGBUILD** instead of file-injection. Under pacman

scripts/customize.sh

@@ -156,6 +156,16 @@ else
   echo "!! package install failed (continuing)"
 fi
 
+# WiFi power management: the brcmfmac driver occasionally puts the chip to
+# sleep and fails to recover, causing rare WiFi drops that require a manual
+# reconnect. Disable power saving permanently for all connections.
+echo "==> [chroot] disabling WiFi power save (brcmfmac)"
+mkdir -p /etc/NetworkManager/conf.d
+cat > /etc/NetworkManager/conf.d/wifi-powersave-off.conf <<'EOF'
+[connection]
+wifi.powersave=2
+EOF
+
 # --- Internal speaker amplifier enable -------------------------------
 # The uConsole's onboard speaker amplifier is gated by an enable GPIO
 # (BCM11 / gpiochip0 line 11). Headphones bypass the amp, so without this the