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backlight: do nothing if max_brightness is 0

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On virtually any newer Asus mainboard, the eeepc-wmi driver is loaded.
It exposes a backlight device despite the lack of any physical backlight
devices. This fake backlight device has max_brightness set to 0. Since
the introduction of the clamp_brightness function, systemd-backlight
tries to write '1' to brightness and fails.

This patch changes systemd-backlight to exit gracefully when
max_brightness is 0 before performing any action. This affects
both the load and save actions.
This commit is contained in:
Thomas Bächler 2014-03-27 23:41:59 +01:00 committed by Tom Gundersen
parent 51e430a5b0
commit 3cadce7d33
1 changed files with 31 additions and 15 deletions
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46
src/backlight/backlight.c
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@ -192,30 +192,37 @@ 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) {
static unsigned get_max_brightness(struct udev_device *device) {
int r;
const char *max_brightness_str;
unsigned brightness, max_brightness, new_brightness;
unsigned max_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;
log_warning("Failed to read max_brightness attribute");
return 0;
}
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 0;
}
return max_brightness;
}
/* 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, unsigned max_brightness) {
int r;
unsigned brightness, new_brightness;
r = safe_atou(*value, &brightness);
if (r < 0) {
log_warning("Failed to parse brightness \"%s\": %s", *value, strerror(-r));
return;
}
@ -239,6 +246,7 @@ int main(int argc, char *argv[]) {
_cleanup_udev_device_unref_ struct udev_device *device = NULL;
_cleanup_free_ char *saved = NULL, *ss = NULL, *escaped_ss = NULL, *escaped_sysname = NULL, *escaped_path_id = NULL;
const char *sysname, *path_id;
unsigned max_brightness;
int r;
if (argc != 3) {
@ -294,6 +302,14 @@ int main(int argc, char *argv[]) {
return EXIT_FAILURE;
}
/* If max_brightness is 0, then there is no actual backlight
* device. This happens on desktops with Asus mainboards
* that load the eeepc-wmi module.
*/
max_brightness = get_max_brightness(device);
if (max_brightness == 0)
return EXIT_SUCCESS;
escaped_ss = cescape(ss);
if (!escaped_ss) {
log_oom();
@ -348,7 +364,7 @@ int main(int argc, char *argv[]) {
return EXIT_FAILURE;
}
clamp_brightness(device, &value);
clamp_brightness(device, &value, max_brightness);
r = udev_device_set_sysattr_value(device, "brightness", value);
if (r < 0) {