From 7b909d7407965c03caaba30daae7aee113627a83 Mon Sep 17 00:00:00 2001 From: Josh Triplett Date: Tue, 11 Mar 2014 21:16:33 -0700 Subject: [PATCH] backlight: Avoid restoring brightness to an unreadably dim level 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. --- src/backlight/backlight.c | 44 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 44 insertions(+) diff --git src/backlight/backlight.c src/backlight/backlight.c index 81470b3..abf8bcf 100644 --- src/backlight/backlight.c +++ 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)); -- 1.7.9.2