https://bugzilla.kernel.org/show_bug.cgi?id=47841
Aaron Lu <aaron...@intel.com> changed:
What |Removed |Added
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CC| |aaron...@intel.com
AssignedTo|acpi_acpica-core@kernel-bug |aaron...@intel.com
|s.osdl.org |
--- Comment #25 from Aaron Lu <aaron...@intel.com> 2013-04-10 01:57:46 ---
(In reply to comment #24)
> ~~~~~~~~~~~
> Conclusions
> ~~~~~~~~~~~
> On this machine I think one should go with acpi_backlight=vendor and wait for
> a
> correct backlight uevent support by desktop environments.
Right.
>
> Still it is unclear to me which is the interaction path between desktop power
> management and the files under /sys/class/backlight (i.e. see points A5 and
> B5). I would be glad if anyone can explain that.
Documentation/ABI/stable/sysfs-class-backlight has some info on these files.
Usually, when hotkey is pressed to adjust backlight, there are three cases:
1 A keycode is generate to user space. In this case, we need to remap the
keycode to standard backlight brightness up/down code, so that user space can
react accordingly(the remap can either be done by driver or by udev);
2 Firmware sends driver a notification, and driver will send a key event(e.g.
standard brightness up/down key code) corresponding to this notification to
user space, so user space can again react accordingly;
3 Firmware directly manipulates the backlight and then sends driver a
notification and driver will send user space an uevent to let them know
something has already happened.
For the first 2 cases, user space will adjust the backlight level through one
of the available backlight interfaces in /sys/class/backlight.
And after any of the operations of the above 3 cases, the file's content may
have changed.
>
> And still I could not understand why the generic ACPI drivers are preferred by
> default over the specific ones, which are supposed to better handle the
> devices. Could anyone explain that too?
GNOME did this, I don't know why.
The gnome-settings-daemon code showed that, g-s-d will prefer backlight
interface of the following order: firmware(acpi_video) >
platform(asus/acer/etc._wmi) > raw (intel/radeon/etc._backlight)
>
> Sorry for the lenghty post, but I tried to be exhaustive. Thanks!
It's very clear, thanks.
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