OLED panel brightness support

[Jani Nikula]

On Mon, 29 Jul 2019, Kai-Heng Feng <kai.heng.feng at canonical.com> wrote:
> at 16:26, Jani Nikula <jani.nikula at linux.intel.com> wrote:
>
>> 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.
>
> I am told that Windows introduced “NitsBrightness” [1] to support OLED panel.
> I don’t know how it’s plumbed to the aux interface though.

That would be about what the numbers we expose to userspace mean. That's
a completely different problem from the kernel not being able to adjust
the brightness of a panel, OLED or not, via the DPCD because of the
non-standard interface being used.

BR,
Jani.


>
> Is it possible to ask Windows graphics team how Windows handle OLED panel?
>
> [1]  
> https://docs.microsoft.com/en-us/windows-hardware/drivers/ddi/content/d3dkmdt/ns-d3dkmdt-_dxgk_brightness_caps
>
> Kai-Heng
>
>>
>> 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
>
>

-- 
Jani Nikula, Intel Open Source Graphics Center