testsAndMisc/linux_configuration/fixes/fix_webcam_c270.sh
Krzysztof kuhy Rudnicki cf55091e95
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fix(webcam): keep Logitech C270 at 30 fps in low light via udev rule
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
2026-10-12 13:49:17 +02:00

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#!/bin/bash
# ============================================================================
# Logitech C270: keep a steady 30 fps in low light (udev rule)
#
# Disables exposure_dynamic_framerate on every plug-in/boot, so auto exposure
# can no longer drop the camera to ~15 fps. Trade-off: a darker image in dim
# rooms. Rationale lives in 99-c270-fixed-framerate.rules.
#
# fix_webcam_c270.sh install the rule and apply it now
# fix_webcam_c270.sh --remove remove the rule (camera default returns on replug)
# fix_webcam_c270.sh --status show rule state and the live control value
# ============================================================================
set -euo pipefail
SCRIPT_NAME="$(basename "$0")"
SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
readonly SCRIPT_NAME SCRIPT_DIR
readonly RULE_NAME="99-c270-fixed-framerate.rules"
readonly RULE_SRC="$SCRIPT_DIR/$RULE_NAME"
readonly RULE_DST="/etc/udev/rules.d/$RULE_NAME"
readonly CONTROL="exposure_dynamic_framerate"
# Overridable so the tests can point it at a fake sysfs tree.
readonly V4L_SYSFS="${C270_V4L_SYSFS:-/sys/class/video4linux}"
log() { echo "[$SCRIPT_NAME] $*"; }
# The C270's capture node (index 0); empty when the camera is unplugged.
find_device() {
local node
for node in "$V4L_SYSFS"/video*; do
[[ -e "$node" ]] || continue
if [[ "$(cat "$node/index")" == 0 ]] &&
grep -qx 0825 "$node/device/../idProduct" 2>/dev/null &&
grep -qx 046d "$node/device/../idVendor" 2>/dev/null; then
echo "/dev/$(basename "$node")"
return
fi
done
}
install_rule() {
pacman -Q v4l-utils &>/dev/null || sudo pacman -S --needed --noconfirm v4l-utils
sudo install -m 644 "$RULE_SRC" "$RULE_DST"
sudo udevadm control --reload
log "installed $RULE_DST"
local dev
dev="$(find_device)"
if [[ -n "$dev" ]]; then
v4l2-ctl -d "$dev" -c "$CONTROL=0"
log "applied to $dev now"
else
log "C270 not plugged in; rule applies on next plug-in"
fi
}
remove_rule() {
sudo rm -f "$RULE_DST"
sudo udevadm control --reload
log "removed $RULE_DST"
}
show_status() {
if [[ -f "$RULE_DST" ]]; then
log "rule: installed"
else
log "rule: not installed"
fi
local dev
dev="$(find_device)"
if [[ -n "$dev" ]]; then
log "$dev: $(v4l2-ctl -d "$dev" -C "$CONTROL")"
else
log "C270 not plugged in"
fi
}
case "${1:-}" in
"") install_rule ;;
--remove) remove_rule ;;
--status) show_status ;;
-h | --help) sed -n '4,13p' "$0" | sed 's/^# \{0,3\}//' ;;
*)
log "unknown option: $1"
exit 2
;;
esac