OLED panel brightness support

[Jani Nikula]

On Tue, 23 Jul 2019, Kai-Heng Feng <kai.heng.feng at canonical.com> wrote:
> Hi,
>
> Currently, OLED panel brightness [1] is not supported.

As a general statement this is not true, and not backed up by the
referenced bug. We just don't know how brightness is controlled on that
particular laptop, because it apparently uses a properietary mechanism.

If it used the brightness control mechamism specified in the VESA eDP
spec, it should work just fine with the i915 aux backlight support, and
we should also export the regular backlight sysfs for this.

BR,
Jani.


> We have a similar Dell system that also affect by lack of OLED brightness  
> support.
>
> I’ve investigated both kernel and user space but I haven’t found a good  
> general solution yet.
> Dell systems use EDID descriptor 4 as Dell specific descriptor, which  
> reports its panel type and we can know it’s an OLED panel or not.
>
> My initial thought is to add a new attribute “oled" in drm_sysfs.c [2] to  
> let userspace like clutter [3] to control the brightness.
> However other DEs may need to implement their own OLED brightness support  
> which isn’t ideal.
>
> So I’d like to know if there’s any good way to support OLED brightness in  
> good old backlight sysfs, to let userspace keep to the current interface.
>
> [1] https://bugs.freedesktop.org/show_bug.cgi?id=97883
> [2] https://pastebin.ubuntu.com/p/QYrRBppVT9/
> [3]  
> https://gitlab.gnome.org/GNOME/clutter/blob/master/clutter/clutter-brightness-contrast-effect.c#L559
>
> Kai-Heng

-- 
Jani Nikula, Intel Open Source Graphics Center