[systemd-devel] [PATCH] backlight: handle saved brightness exceeding max brightness

[Jani Nikula]

On Wed, 07 May 2014, Jani Nikula <jani.nikula at intel.com> wrote:
> If too high a brightness value has been saved (e.g. due to kernel
> mechanism changing from one kernel version to another, or booting the
> userspace on another system), the brightness update fails and the
> process exits.
>
> Clamp saved brightness between the policy minimum introduced in
>
> commit 7b909d7407965c03caaba30daae7aee113627a83
> Author: Josh Triplett <josh at joshtriplett.org>
> Date:   Tue Mar 11 21:16:33 2014 -0700
>
>     backlight: Avoid restoring brightness to an unreadably dim level
>
> and the absolute maximum.
>
> ---
>
> UNCOMPILED AND UNTESTED; please consider this more a bug report than a
> real contribution... Based on reading the source while debugging
> https://bugs.freedesktop.org/show_bug.cgi?id=78200
> ---
>  src/backlight/backlight.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/src/backlight/backlight.c b/src/backlight/backlight.c
> index c708391612a2..d48a73e69364 100644
> --- a/src/backlight/backlight.c
> +++ b/src/backlight/backlight.c
> @@ -229,7 +229,7 @@ static unsigned get_max_brightness(struct udev_device *device) {
>   * 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;
> +        unsigned brightness, new_brightness, min_brightness;
>  
>          r = safe_atou(*value, &brightness);
>          if (r < 0) {
> @@ -237,7 +237,8 @@ static void clamp_brightness(struct udev_device *device, char **value, unsigned
>                  return;
>          }
>  
> -        new_brightness = MAX3(brightness, 1U, max_brightness/20);
> +        min_brightness = MAX(1U, max_brightness/20);
> +        new_brightness = CLAMP(brightness, min_brightness, max_brightness);
>          if (new_brightness != brightness) {
>                  char *old_value = *value;
>  
> @@ -247,7 +248,11 @@ static void clamp_brightness(struct udev_device *device, char **value, unsigned
>                          return;
>                  }
>  
> -                log_debug("Saved brightness %s too low; increasing to %s.", old_value, *value);
> +                log_debug("Saved brightness %s %s to %s.", old_value,
> +                          new_brightness < min_brightness ?

Should be "brightness < min_brightness"; the above is never true.

> +                          "too low; increasing" : "too high; decreasing",
> +                          *value);
> +
>                  free(old_value);
>          }
>  }
> -- 
> 1.9.1
>

-- 
Jani Nikula, Intel Open Source Technology Center