[systemd-devel] [PATCH] backlight: do nothing if max_brightness is 0

[Thomas Bächler]

Am 23.04.2014 07:00, schrieb Lennart Poettering:
> On Thu, 27.03.14 23:41, Thomas Bächler (thomas at archlinux.org) wrote:
> 
>> 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.
> 
> Humm. To me this appears like the driver is broken. The kernel should
> not expose a backlight device if there isn't any backend to it?

Yes.

> Have you
> filed a kernel bug?

No, I'll take care of it though.

> I have changed git now to still print a warning in this case, as we
> shouldn't silently tape over broken drivers.

Very good. While we should not try to work with nonsense brightness
values, a warning is perfectly fine.


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