Gabriel Brown
6510fdda0f
ddcutil's udev rule grants the seated user the GPU's i2c buses only when the PCI class is 0x030000. An AMD iGPU that is not the primary boot display says 0x038000, so on the Framework every DDC bus stayed root-only. Ship the same grant for the class the hardware actually reports; change-settings installs it. And two conflations in the probe: an undocked laptop reported its normal state as an error, and doctor collapsed every error into "No accessible DDC/CI bus". Nothing external connected is now a clean empty -- doctor's unconfigured path -- and a real failure surfaces the probe's own words, because an unreadable bus and a monitor with DDC/CI off in its menu have different fixes. Claude-Session: https://claude.ai/code/session_01Epx9ZC1gwm81K3jm9x9CKh
173 lines
7.2 KiB
Bash
Executable File
173 lines
7.2 KiB
Bash
Executable File
#!/usr/bin/env bash
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# External monitor brightness over DDC/CI.
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#
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# A desktop with no backlight class device has no brightness control at all --
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# brightnessctl only sees keyboard and NIC LEDs. The panel itself still has a
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# brightness setting, reachable over the monitor's DDC/CI channel (VCP feature
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# 0x10), which is what the buttons on the bezel drive.
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#
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# Usage:
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# panama-brightness list -> {"displays":[...],"error":""}
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# panama-brightness get <bus> -> integer percent
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# panama-brightness set <bus> <pct> -> applies, prints nothing
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#
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# Displays are enumerated from sysfs rather than from `ddcutil detect`. The
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# kernel publishes the connector-to-I2C-bus mapping directly, as
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# /sys/class/drm/<card>-<connector>/ddc, along with whether anything is plugged
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# in. That is better than parsing detect output in three ways: the format is
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# stable where detect's brief output is undocumented, the connector name comes
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# out exactly as Hyprland and the Displays page already spell it (DP-2), and
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# only connectors with a monitor attached get probed -- one bus on this machine
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# instead of fourteen, which is the difference between a fast scan and a slow
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# one, since each probe of an empty bus waits for a timeout.
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#
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# No model name is reported. Hyprland already knows the human-readable
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# description of every output, so the UI joins on the connector name rather than
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# having two sources of truth for what a monitor is called.
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set -uo pipefail
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readonly VCP_BRIGHTNESS=0x10
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# Test seams. The contract needs to exercise enumeration and parsing on a
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# machine whose real monitors it must not touch, so both roots this script
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# reads are overridable. Nothing sets them in normal use.
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readonly DRM_ROOT="${PANAMA_BRIGHTNESS_DRM_ROOT:-/sys/class/drm}"
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readonly DEV_ROOT="${PANAMA_BRIGHTNESS_DEV_ROOT:-/dev}"
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emit_error() {
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printf '{"displays":[],"error":%s}\n' "$(jq -Rn --arg e "$1" '$e')"
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exit 0
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}
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command -v ddcutil >/dev/null 2>&1 || emit_error 'ddcutil is not installed'
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# Reading a VCP value needs read/write access to the monitor's I2C bus. The
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# udev rule ddcutil ships grants that to the seat user through uaccess, but only
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# to devices created after the rule was installed -- so a machine that installed
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# ddcutil without rebooting has the rule in place and no access to show for it.
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# That is by far the most likely reason for an empty list, and it is fixable in
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# one command, so say so rather than reporting "no displays".
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has_accessible_bus() {
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local dev
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for dev in "$DEV_ROOT"/i2c-*; do
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[[ -r "$dev" && -w "$dev" ]] && return 0
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done
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return 1
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}
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# The I2C bus that carries DDC/CI for one connector.
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#
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# There are two, and picking the wrong one finds no monitor at all:
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#
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# DisplayPort carries DDC/CI over the AUX channel. That adapter shows up as a
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# child directory of the connector -- /sys/class/drm/card1-DP-2/i2c-9 -- and
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# is the one ddcutil talks to.
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#
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# The connector's `ddc` symlink points at the classic I2C line used for EDID
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# on HDMI and DVI. On a DisplayPort connector it still exists and still
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# resolves, but nothing answers on it: this machine's DP-2 has ddc -> i2c-5,
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# where ddcutil reports "No monitor detected", while i2c-9 answers VCP 0x10
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# immediately.
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#
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# So prefer the AUX child and fall back to the symlink. Note the readlink: the
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# entries under /sys/class/drm are symlinks, and `find` does not follow the path
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# it is given, so searching the unresolved path silently finds nothing.
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bus_for_connector() {
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local path="$1" real aux ddc
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real="$(readlink -f "$path")"
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aux="$(find "$real" -maxdepth 1 -name 'i2c-*' -printf '%f' -quit 2>/dev/null)"
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if [[ -n "$aux" ]]; then
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printf '%s' "${aux#i2c-}"
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return 0
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fi
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ddc="$(readlink -f "$path/ddc" 2>/dev/null)" || return 1
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[[ -n "$ddc" ]] || return 1
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ddc="$(basename "$ddc")"
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printf '%s' "${ddc#i2c-}"
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}
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cmd_list() {
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has_accessible_bus || emit_error 'no I2C bus is accessible. ddcutil ships a udev rule that grants this, but only to devices created after it was installed. Run: sudo udevadm control --reload-rules && sudo udevadm trigger --subsystem-match=i2c-dev --subsystem-match=drm'
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local rows=() externals=0 connector bus value path
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for path in "$DRM_ROOT"/card*-*; do
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[[ -e "$path/ddc" ]] || continue
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[[ "$(cat "$path/status" 2>/dev/null)" == "connected" ]] || continue
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# card1-DP-2 -> DP-2, the name Hyprland uses.
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connector="$(basename "$path")"
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connector="${connector#card*-}"
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# Internal panels (eDP, LVDS, DSI) use the backlight, never DDC/CI.
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# Counting only external connectors lets the empty result below say
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# whether anything is even plugged in.
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case "$connector" in
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eDP-*|LVDS-*|DSI-*) ;;
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*) externals=$((externals + 1)) ;;
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esac
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bus="$(bus_for_connector "$path")"
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[[ "$bus" =~ ^[0-9]+$ ]] || continue
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# A monitor that does not implement 0x10 is not an error; it simply
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# cannot be controlled, and is left out rather than shown as a slider
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# that does nothing.
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value="$(cmd_get "$bus")" || continue
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[[ -n "$value" ]] || continue
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rows+=("$(jq -cn \
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--argjson bus "$bus" \
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--arg connector "$connector" \
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--argjson value "$value" \
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'{bus: $bus, connector: $connector, value: $value}')")
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done
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if [[ ${#rows[@]} -eq 0 ]]; then
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# Nothing external is connected at all: the normal state of an
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# undocked laptop, not a problem to warn about. The error path is
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# reserved for a monitor that is present but will not talk.
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if (( externals == 0 )); then
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printf '{"displays":[],"error":""}\n'
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return 0
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fi
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emit_error 'no connected monitor reports DDC/CI brightness. Some panels implement it only when "DDC/CI" is enabled in their on-screen menu.'
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fi
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printf '{"displays":[%s],"error":""}\n' "$(IFS=,; printf '%s' "${rows[*]}")"
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}
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# Prints the current brightness as a whole percent, or nothing when the display
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# cannot report it. `getvcp --brief` is documented as machine readable and
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# answers "VCP 10 C <current> <max>"; the max is almost always 100 but is not
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# guaranteed to be, so it is read rather than assumed.
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cmd_get() {
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local bus="$1" out current max
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out="$(timeout 10 ddcutil --bus "$bus" getvcp "$VCP_BRIGHTNESS" --brief 2>/dev/null)" || return 1
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read -r _ _ _ current max <<<"$out"
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[[ "$current" =~ ^[0-9]+$ && "$max" =~ ^[0-9]+$ && "$max" -gt 0 ]] || return 1
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printf '%s' "$(( current * 100 / max ))"
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}
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cmd_set() {
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local bus="$1" percent="$2" max out
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[[ "$percent" =~ ^[0-9]+$ ]] || return 1
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(( percent > 100 )) && percent=100
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out="$(timeout 10 ddcutil --bus "$bus" getvcp "$VCP_BRIGHTNESS" --brief 2>/dev/null)" || return 1
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read -r _ _ _ _ max <<<"$out"
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[[ "$max" =~ ^[0-9]+$ && "$max" -gt 0 ]] || max=100
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timeout 10 ddcutil --bus "$bus" setvcp "$VCP_BRIGHTNESS" "$(( percent * max / 100 ))" >/dev/null 2>&1
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}
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case "${1:-list}" in
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list) cmd_list ;;
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get) cmd_get "${2:?bus required}" ;;
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set) cmd_set "${2:?bus required}" "${3:?percent required}" ;;
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*) printf 'usage: panama-brightness [list|get <bus>|set <bus> <percent>]\n' >&2; exit 2 ;;
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esac
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