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-rw-r--r--src/backlight/backlight.c44
1 files changed, 44 insertions, 0 deletions
diff --git a/src/backlight/backlight.c b/src/backlight/backlight.c
index 81470b3f9d..abf8bcf00e 100644
--- a/src/backlight/backlight.c
+++ b/src/backlight/backlight.c
@@ -192,6 +192,48 @@ static bool validate_device(struct udev *udev, struct udev_device *device) {
return true;
}
+/* Some systems turn the backlight all the way off at the lowest levels.
+ * clamp_brightness clamps the saved brightness to at least 1 or 5% of
+ * max_brightness. This avoids preserving an unreadably dim screen, which
+ * would otherwise force the user to disable state restoration. */
+static void clamp_brightness(struct udev_device *device, char **value) {
+ int r;
+ const char *max_brightness_str;
+ unsigned brightness, max_brightness, new_brightness;
+
+ max_brightness_str = udev_device_get_sysattr_value(device, "max_brightness");
+ if (!max_brightness_str) {
+ log_warning("Failed to read max_brightness attribute; not checking saved brightness");
+ return;
+ }
+
+ r = safe_atou(*value, &brightness);
+ if (r < 0) {
+ log_warning("Failed to parse brightness \"%s\": %s", *value, strerror(-r));
+ return;
+ }
+
+ r = safe_atou(max_brightness_str, &max_brightness);
+ if (r < 0) {
+ log_warning("Failed to parse max_brightness \"%s\": %s", max_brightness_str, strerror(-r));
+ return;
+ }
+
+ new_brightness = MAX3(brightness, 1U, max_brightness/20);
+ if (new_brightness != brightness) {
+ char *old_value = *value;
+
+ r = asprintf(value, "%u", new_brightness);
+ if (r < 0) {
+ log_oom();
+ return;
+ }
+
+ log_debug("Saved brightness %s too low; increasing to %s.", old_value, *value);
+ free(old_value);
+ }
+}
+
int main(int argc, char *argv[]) {
_cleanup_udev_unref_ struct udev *udev = NULL;
_cleanup_udev_device_unref_ struct udev_device *device = NULL;
@@ -306,6 +348,8 @@ int main(int argc, char *argv[]) {
return EXIT_FAILURE;
}
+ clamp_brightness(device, &value);
+
r = udev_device_set_sysattr_value(device, "brightness", value);
if (r < 0) {
log_error("Failed to write system attribute: %s", strerror(-r));