fix(sxmo): re-enable automatic screen-off on idle to stop backlight battery drain

The previous commit disabled sxmo_idle.sh and the idle_locker in the
unlock/lock hooks, leaving the display backlight pinned at maximum
brightness forever (Xorg runs with -s 0 -dpms and /sys/power/state is
empty, so the panel never blanks). On a phone with no suspend this is by
far the dominant battery drain.

Restore sxmo_idle.sh and start idle_locker from the unlock and lock hooks
so the screen blanks after SXMO_UNLOCK_IDLE_TIME (default 30s) / once
locked after SXMO_LOCK_IDLE_TIME (default 8s). Locking itself stays
explicit-only, matching the documented design; only the display blanks.

Verified live on the device: after the idle timeout the state transitions
to screenoff and /sys/class/backlight/backlight/brightness drops to 0.

MANUAL.md

@@ -118,7 +118,7 @@ sudo dd if=./images/bananarchy-nokia-argon.img of=/dev/sdX bs=4M status=progress
 | **Slider close / open** | `SW_LID` (`lid:on` / `lid:off`) | **Close**: close open menu, turn off keypad backlight, and lock/turn screen off; **Open**: restore keypad backlight, unlock, and turn screen on |
 
 > **Explicit locking & waking**:
-> X11 screensaver/DPMS blanking and automatic idle locking are disabled so the phone only locks when explicitly requested (`Power -> Lock / Lock (Screen off)`, `XDrawer -> Lock`, `2× End / Power`, or closing the physical slider). When locked, you can wake and unlock the phone in a single action by either:
+> X11 screensaver/DPMS blanking is disabled (the display is blanked explicitly by Sxmo, not by the X server), and automatic idle *locking* is disabled so the phone only locks when explicitly requested (`Power -> Lock / Lock (Screen off)`, `XDrawer -> Lock`, `2× End / Power`, or closing the physical slider). To save battery, the display still blanks automatically after a period of inactivity (`SXMO_UNLOCK_IDLE_TIME`, default 30s; `SXMO_LOCK_IDLE_TIME`, default 8s once locked) without locking. When the screen is off, you can wake and unlock the phone in a single action by either:
 > - **Opening the slider** (`SW_LID` off), or
 > - Pressing **End / Power (red)**, **Left softkey**, **Right softkey**, or **Call (green)** once.
 

overlay/rootfs/usr/bin/sxmo_idle.sh

@@ -1,4 +1,78 @@
 #!/bin/sh
 # SPDX-License-Identifier: AGPL-3.0-only
-# Automatic idle locking and screen blanking are disabled on Bananarchy.
-exit 0
+# Copyright 2022 Sxmo Contributors
+
+_swayidletoidles() {
+	while [ $# -gt 0 ]; do
+		case "$1" in
+			timeout)
+				printf "%s|%s" "$2" "$3"
+				shift 3
+				case "$1" in
+					resume)
+						printf "|%s" "$2"
+						shift 2
+				;;
+				esac
+				printf "\n"
+				;;
+			*)
+				shift
+				;;
+		esac
+	done
+}
+
+xorgidle() {
+	if ! command -v xprintidle >/dev/null 2>&1; then
+		while : ; do
+			sleep 3600
+		done
+	fi
+
+	idles="$(_swayidletoidles "$@")"
+	resumes=""
+
+	tick=0
+	new_idle="$(xprintidle 2>/dev/null || printf '0')"
+	[ -n "$new_idle" ] || new_idle=0
+	last_idle="$new_idle"
+
+	finish() {
+		sh -c "$resumes"
+		resumes=""
+		exit
+	}
+	trap 'finish' TERM INT EXIT
+
+	while : ; do
+		last_idle="$new_idle"
+		new_idle="$(xprintidle 2>/dev/null || printf '0')"
+		[ -n "$new_idle" ] || new_idle=0
+		if [ "$last_idle" -gt "$new_idle" ] 2>/dev/null; then
+			sh -c "$resumes"
+			tick=0
+			resumes=""
+		fi
+
+		if printf "%b\n" "$idles" | grep -q "^$tick|"; then
+			printf "%b\n" "$idles" | \
+				grep "^$tick|" | \
+				cut -d'|' -f2 | \
+				xargs -I{} -0 sh -c "{}"
+			resumes="$(printf "%b\n" "$idles" | grep "^$tick|" | cut -d'|' -f3);$resumes"
+		fi
+
+		sleep 1
+		tick=$((tick + 1))
+	done
+}
+
+case "$SXMO_WM" in
+	dwm|i3)
+		xorgidle "$@"
+		;;
+	sway|river)
+		exec swayidle "$@"
+		;;
+esac

overlay/rootfs/usr/share/sxmo/default_hooks/sxmo_hook_lock.sh

@@ -32,7 +32,14 @@ if [ -z "$SXMO_DISABLE_LEDS" ]; then
 fi
 sxmo_jobs.sh stop periodic_wakelock_check
 
-# Automatic idle transitions are disabled; only explicit locking is used
-sxmo_jobs.sh stop idle_locker 2>/dev/null || true
+# Re-enable automatic screen-off on idle to save battery. The phone only
+# locks on explicit request; once locked we blank the screen after a short
+# idle period.
+if [ -e "$XDG_CACHE_HOME/sxmo/sxmo.noidle" ]; then
+	sxmo_jobs.sh stop idle_locker
+else
+	sxmo_jobs.sh start idle_locker sxmo_idle.sh -w \
+		timeout "${SXMO_LOCK_IDLE_TIME:-8}" 'sh -c "sxmo_state.sh set screenoff"'
+fi
 
 wait

overlay/rootfs/usr/share/sxmo/default_hooks/sxmo_hook_unlock.sh

@@ -26,7 +26,13 @@ if [ -z "$SXMO_DISABLE_LEDS" ]; then
 fi
 sxmo_jobs.sh stop periodic_wakelock_check
 
-# Automatic idle locking is disabled; only explicit locking is used
-sxmo_jobs.sh stop idle_locker 2>/dev/null || true
+# Re-enable automatic screen-off on idle to save battery. Locking stays
+# explicit (the user locks only on request); we only blank the display.
+if [ -e "$XDG_CACHE_HOME/sxmo/sxmo.noidle" ]; then
+	sxmo_jobs.sh stop idle_locker
+else
+	sxmo_jobs.sh start idle_locker sxmo_idle.sh -w \
+		timeout "${SXMO_UNLOCK_IDLE_TIME:-30}" 'sh -c "sxmo_state.sh set screenoff"'
+fi
 
 wait