From 2d4460027359d91f442d2677e9ae42ea951e2430 Mon Sep 17 00:00:00 2001

From: =?UTF-8?q?Thomas=20B=C3=A4chler?= <thomas@archlinux.org>

Date: Thu, 27 Mar 2014 23:41:59 +0100

Subject: [PATCH] backlight: do nothing if max_brightness is 0

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.

(cherry picked from commit 3cadce7d33e263ec7a6a83c00c11144930258b22)

(cherry picked from commit 555853f8ad1b1db461c45843310bc324bca394de)

---

 src/backlight/backlight.c | 44 ++++++++++++++++++++++++++++++--------------

 1 file changed, 30 insertions(+), 14 deletions(-)

diff --git a/src/backlight/backlight.c b/src/backlight/backlight.c

index 2740b80..84bf51d 100644

--- a/src/backlight/backlight.c

+++ b/src/backlight/backlight.c

@@ -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;

+                log_warning("Failed to read max_brightness attribute");

+                return 0;

         }

-        r = safe_atou(*value, &brightness);

+        r = safe_atou(max_brightness_str, &max_brightness);

         if (r < 0) {

-                log_warning("Failed to parse brightness \"%s\": %s", *value, strerror(-r));

-                return;

+                log_warning("Failed to parse max_brightness \"%s\": %s", max_brightness_str, strerror(-r));

+                return 0;

         }

-        r = safe_atou(max_brightness_str, &max_brightness);

+        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 max_brightness \"%s\": %s", max_brightness_str, strerror(-r));

+                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) {