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backlight: Avoid restoring brightness to an unreadably dim level

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Some systems turn the backlight all the way off at the lowest levels.
Clamp 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.
This commit is contained in:
Josh Triplett 2014-03-11 21:16:33 -07:00 committed by Lennart Poettering
parent cddc35f75e
commit 7b909d7407
1 changed files with 44 additions and 0 deletions
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44
src/backlight/backlight.c
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@ -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));