Route an all-in-one's built-in panel to the kernel backlight

bin/omarchy-brightness-display

@@ -6,6 +6,11 @@
 
 no_osd=0
 monitor=""
+drm_path="${OMARCHY_DRM_PATH:-/sys/class/drm}"
+
+# omarchy-brightness-display-ddc's "this connector answers no DDC display",
+# as opposed to a transient read failure worth retrying.
+no_ddc_display=3
 
 while (( $# > 0 )); do
   case "$1" in
@@ -35,6 +40,29 @@ monitor_is_internal() {
   [[ $monitor =~ ^(eDP|LVDS|DSI)- ]]
 }
 
+# All-in-ones wire their built-in panel to a DisplayPort connector, so its
+# output name carries no hint that it is internal and the panel gets routed to
+# DDC/CI, which a built-in panel does not answer. The kernel backlight is the
+# right target there -- but only on a machine with no eDP/LVDS/DSI connector to
+# own that backlight instead, or a laptop's DDC-less external monitor would move
+# the laptop's own panel. Read the connectors rather than counting Hyprland
+# outputs: Hyprland invents a FALLBACK output when every monitor is disabled.
+machine_has_internal_connector() {
+  local status
+
+  for status in "$drm_path"/card*-*/status; do
+    [[ -e $status ]] || continue
+    [[ $status =~ -(eDP|LVDS|DSI)-[^/]+/status$ ]] || continue
+    [[ $(<"$status") == "connected" ]] && return 0
+  done
+
+  return 1
+}
+
+backlight_owns_named_monitor() {
+  ! machine_has_internal_connector && omarchy-hw-display >/dev/null 2>&1
+}
+
 use_apple_display() {
   omarchy-hyprland-monitor-focused-apple "$monitor"
 }
@@ -49,7 +77,9 @@ if (( $# == 0 )); then
     exit
   elif use_ddc_display; then
     omarchy-brightness-display-ddc "$monitor"
-    exit
+    ddc_status=$?
+    (( ddc_status == 0 )) && exit 0
+    (( ddc_status == no_ddc_display )) && backlight_owns_named_monitor || exit 1
   fi
 
   device="$(omarchy-hw-display)" || exit 1
@@ -82,41 +112,49 @@ if use_apple_display; then
   else
     omarchy-brightness-display-apple "$step"
   fi
-elif use_ddc_display; then
-  brightness="$(omarchy-brightness-display-ddc "$monitor" "$step")" || exit 1
-  (( no_osd )) || omarchy-osd -i brightness -p "$brightness"
-else
-  # Current device highlighted
-  device="$(omarchy-hw-display)" || exit 1
+  exit
+fi
 
-  # Current brightness percentage
-  current=$(backlight_brightness "$device") || exit 1
-
-  # Apply non-uniform step size: 1% steps if at or below 5%, otherwise set an
-  # absolute target percentage to avoid raw backlight rounding causing uneven OSD steps.
-  if [[ $step == "+5%" ]]; then
-    if (( current < 5 )); then
-      (( target = current + 1 ))
-    else
-      (( target = current + 5 ))
-    fi
-
-    (( target > 100 )) && target=100
-    step="$target%"
-  elif [[ $step == "5%-" ]]; then
-    if (( current <= 5 )); then
-      (( target = current - 1 ))
-    else
-      (( target = current - 5 ))
-    fi
-
-    (( target < 1 )) && target=1
-    step="$target%"
+if use_ddc_display; then
+  brightness="$(omarchy-brightness-display-ddc "$monitor" "$step")"
+  ddc_status=$?
+  if (( ddc_status == 0 )); then
+    (( no_osd )) || omarchy-osd -i brightness -p "$brightness"
+    exit 0
   fi
+  (( ddc_status == no_ddc_display )) && backlight_owns_named_monitor || exit 1
+fi
 
-  # Set brightness of the display device.
-  brightnessctl -d "$device" set "$step" >/dev/null
+# Current device highlighted
+device="$(omarchy-hw-display)" || exit 1
 
-  # Show the new brightness in OSD
-  (( no_osd )) || omarchy-osd -i brightness -p "$(backlight_brightness "$device")"
+# Current brightness percentage
+current=$(backlight_brightness "$device") || exit 1
+
+# Apply non-uniform step size: 1% steps if at or below 5%, otherwise set an
+# absolute target percentage to avoid raw backlight rounding causing uneven OSD steps.
+if [[ $step == "+5%" ]]; then
+  if (( current < 5 )); then
+    (( target = current + 1 ))
+  else
+    (( target = current + 5 ))
+  fi
+
+  (( target > 100 )) && target=100
+  step="$target%"
+elif [[ $step == "5%-" ]]; then
+  if (( current <= 5 )); then
+    (( target = current - 1 ))
+  else
+    (( target = current - 5 ))
+  fi
+
+  (( target < 1 )) && target=1
+  step="$target%"
 fi
+
+# Set brightness of the display device.
+brightnessctl -d "$device" set "$step" >/dev/null
+
+# Show the new brightness in OSD
+(( no_osd )) || omarchy-osd -i brightness -p "$(backlight_brightness "$device")"

bin/omarchy-brightness-display-ddc

@@ -9,6 +9,11 @@ step="${2:-}"
 
 [[ -n $monitor ]] || exit 1
 
+# Distinguishes "this connector answers no DDC display" from a transient read
+# failure, so a caller can route the connector somewhere else rather than retry
+# a bus that is never going to appear.
+no_ddc_display=3
+
 cache_dir="${XDG_RUNTIME_DIR:-/tmp}/omarchy-brightness-display-ddc"
 cache_name="${monitor//[^[:alnum:]_.-]/_}"
 cache_file="$cache_dir/$cache_name.bus"
@@ -51,7 +56,7 @@ find_bus() {
   if [[ $bus == "unavailable" ]]; then
     now=$(date +%s)
     if [[ $cached_value =~ ^[0-9]+$ ]] && (( now - cached_value < unavailable_cache_seconds )); then
-      return 1
+      return "$no_ddc_display"
     fi
     bus=""
     rm -f "$cache_file"
@@ -61,7 +66,7 @@ find_bus() {
     bus="$(detect_bus)" || return 1
     if [[ ! $bus =~ ^[0-9]+$ ]]; then
       cache_unavailable
-      return 1
+      return "$no_ddc_display"
     fi
     mkdir -p "$cache_dir" 2>/dev/null || true
     printf '%s\n' "$bus" >"$cache_file" 2>/dev/null || true
@@ -89,7 +94,7 @@ read_brightness() {
   local now=0
   local values=""
 
-  bus="$(find_bus)" || return 1
+  bus="$(find_bus)" || return $?
   values="$(read_vcp "$bus")" || {
     rm -f "$cache_file"
     return 1
@@ -108,7 +113,8 @@ percent=""
 range_cached_at=""
 
 if [[ -z $step ]]; then
-  read -r bus current maximum < <(read_brightness) || exit 1
+  brightness="$(read_brightness)" || exit $?
+  read -r bus current maximum <<<"$brightness"
   [[ -n ${bus:-} && -n ${current:-} && -n ${maximum:-} ]] || exit 1
   (( percent = (current * 100 + maximum / 2) / maximum ))
   printf '%s\n' "$percent"
@@ -130,10 +136,12 @@ if [[ $step =~ ^([0-9]+)%$ ]]; then
   fi
 
   if (( ! range_cache_fresh )); then
-    read -r bus current maximum < <(read_brightness) || exit 1
+    brightness="$(read_brightness)" || exit $?
+    read -r bus current maximum <<<"$brightness"
   fi
 elif [[ $step =~ ^\+([0-9]+)%$ ]]; then
-  read -r bus current maximum < <(read_brightness) || exit 1
+  brightness="$(read_brightness)" || exit $?
+  read -r bus current maximum <<<"$brightness"
   [[ -n ${bus:-} && -n ${current:-} && -n ${maximum:-} ]] || exit 1
   (( percent = (current * 100 + maximum / 2) / maximum ))
   amount="${BASH_REMATCH[1]}"
@@ -143,7 +151,8 @@ elif [[ $step =~ ^\+([0-9]+)%$ ]]; then
     (( target = percent + amount ))
   fi
 elif [[ $step =~ ^([0-9]+)%-$ ]]; then
-  read -r bus current maximum < <(read_brightness) || exit 1
+  brightness="$(read_brightness)" || exit $?
+  read -r bus current maximum <<<"$brightness"
   [[ -n ${bus:-} && -n ${current:-} && -n ${maximum:-} ]] || exit 1
   (( percent = (current * 100 + maximum / 2) / maximum ))
   amount="${BASH_REMATCH[1]}"

test/shell.d/brightness-display-test.sh

@@ -53,8 +53,27 @@ SH
 
 chmod +x "$mock_bin"/*
 
+# Machine shape, as the kernel presents it. A laptop owns its backlight through
+# an eDP connector; an all-in-one wires its built-in panel to DisplayPort and has
+# no internal-named connector at all. The all-in-one gets both topologies, alone
+# and with a second display attached, so each case runs against the DRM set it
+# actually describes.
+drm_laptop="$test_tmp/drm-laptop"
+drm_aio="$test_tmp/drm-aio"
+drm_aio_docked="$test_tmp/drm-aio-docked"
+mkdir -p "$drm_laptop/card1-eDP-1" "$drm_laptop/card1-DP-2" \
+  "$drm_aio/card1-DP-1" "$drm_aio/card1-DP-2" \
+  "$drm_aio_docked/card1-DP-1" "$drm_aio_docked/card1-DP-2"
+printf 'connected\n' >"$drm_laptop/card1-eDP-1/status"
+printf 'connected\n' >"$drm_laptop/card1-DP-2/status"
+printf 'connected\n' >"$drm_aio/card1-DP-1/status"
+printf 'disconnected\n' >"$drm_aio/card1-DP-2/status"
+printf 'connected\n' >"$drm_aio_docked/card1-DP-1/status"
+printf 'connected\n' >"$drm_aio_docked/card1-DP-2/status"
+
 run_brightness() {
-  CALL_LOG="$call_log" XDG_RUNTIME_DIR="$runtime_dir" PATH="$mock_bin:$ROOT/bin:$PATH" \
+  CALL_LOG="$call_log" XDG_RUNTIME_DIR="$runtime_dir" OMARCHY_DRM_PATH="${DRM_PATH:-$drm_laptop}" \
+    PATH="$mock_bin:$ROOT/bin:$PATH" \
     "$ROOT/bin/omarchy-brightness-display" "$@"
 }
 
@@ -144,3 +163,52 @@ if PATH="$mock_bin:$PATH" "$ROOT/bin/omarchy-hyprland-monitor-focused-apple"; th
   fail "focused non-Apple display is not detected as Apple"
 fi
 pass "named Apple display is detected independently of focus"
+
+# An all-in-one's built-in panel is named DP-1 and answers no DDC display, and
+# the machine has no eDP/LVDS/DSI connector that could own the kernel backlight
+# instead -- so the backlight is the panel behind that connector.
+rm -rf "$runtime_dir/omarchy-brightness-display-ddc"
+brightness=$(DRM_PATH="$drm_aio" DDC_CONNECTOR=DP-9 run_brightness --monitor DP-1) ||
+  fail "all-in-one panel falls back to the kernel backlight" "the command exited nonzero"
+[[ $brightness == "40" ]] || fail "all-in-one panel falls back to the kernel backlight" "actual: $brightness"
+pass "a DisplayPort panel with no DDC display uses the kernel backlight"
+
+rm -rf "$runtime_dir/omarchy-brightness-display-ddc"
+DRM_PATH="$drm_aio" DDC_CONNECTOR=DP-9 run_brightness --no-osd --monitor DP-1 60%
+grep -F 'brightnessctl -d mock_backlight set 60%' "$call_log" >/dev/null ||
+  fail "all-in-one panel sets brightness through the kernel backlight"
+pass "a DisplayPort panel with no DDC display is adjusted through the kernel backlight"
+
+# The same all-in-one with a real external monitor attached and connected: that
+# one answers DDC, so it keeps using it. Only the connector without a DDC display
+# falls back.
+rm -rf "$runtime_dir/omarchy-brightness-display-ddc"
+brightness=$(DRM_PATH="$drm_aio_docked" DDC_CONNECTOR=DP-2 run_brightness --monitor DP-2) ||
+  fail "an external monitor on an all-in-one still uses DDC" "the command exited nonzero"
+[[ $brightness == "50" ]] || fail "an external monitor on an all-in-one still uses DDC" "actual: $brightness"
+pass "an external monitor that answers DDC still uses DDC"
+
+# The built-in panel of that same docked all-in-one still has to reach the
+# backlight. A second connected display is not an internal panel, so it cannot
+# be what the backlight belongs to.
+rm -rf "$runtime_dir/omarchy-brightness-display-ddc"
+brightness=$(DRM_PATH="$drm_aio_docked" DDC_CONNECTOR=DP-2 run_brightness --monitor DP-1) ||
+  fail "a docked all-in-one still drives its own panel" "the command exited nonzero"
+[[ $brightness == "40" ]] || fail "a docked all-in-one still drives its own panel" "actual: $brightness"
+pass "an all-in-one panel keeps the kernel backlight with a second display connected"
+
+# A laptop's DDC-less external monitor must keep failing. Falling back would
+# move the laptop's own panel while the user is asking for the other one.
+rm -rf "$runtime_dir/omarchy-brightness-display-ddc"
+if DRM_PATH="$drm_laptop" DDC_CONNECTOR=DP-9 run_brightness --monitor DP-2 >/dev/null 2>&1; then
+  fail "a laptop's DDC-less external monitor does not move the internal backlight"
+fi
+pass "an external monitor on a machine with an internal panel does not fall back"
+
+# A transient DDC read failure is not "no display on this connector", so it must
+# not fall back either -- the monitor is there and will answer on the next try.
+rm -rf "$runtime_dir/omarchy-brightness-display-ddc"
+if DRM_PATH="$drm_aio" DDC_READ_FAIL=1 run_brightness --monitor DP-1 >/dev/null 2>&1; then
+  fail "a transient DDC read failure does not fall back to the backlight"
+fi
+pass "a transient DDC read failure is not treated as a missing DDC display"