[Bug 97883] [i915] intel_backlight does not function - Lenovo X1 Yoga OLED

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97883

--- Comment #27 from Niklas Kielblock <niklas.kielblock at googlemail.com> ---
(In reply to Marten van Kerkwijk from comment #26)
> ...So, are you sure the driver is in fact proprietary,
> rather than this simply being an oversight? The fact
> that even the windows machines initially couldn't change their brightness
> suggests oversight/incompetence is not an implausible explanation. 

The *protocol* is "proprietary" as in (apparently) vendor-specific and not
publicly documented, and the *driver* is "proprietary" in that it has certainly
never gotten an opensource release; it also utilises an API provided by the
general Windows Intel GPU driver for talking to the display.

Windows systems naturally also depend on this driver, device-specific versions
of which are shipped with all laptops using such a display in addition to being
provided online, to change brightness. The fact that the brightness controls on
Windows don't do anything without it installed appears to be intended
behaviour.

> Also, since formally there is no back light for OLED displays, it is not that
> strange to not think of using the backlight API -- though I certainly would
> have thought it would be very logical to re-purpose that!

(In reply to Jani Nikula from comment #25)
> Suffice it to say, it's not just tracking this down, it's also getting the
> permission to open source something that the display vendor apparently
> deemed best to do in their own proprietary way instead of following the DP
> specs.

Hi Jani, thanks for responding. FWIW, I can see technical reasons for this
decision beyond just politics/NIH. While I'm not sure anybody's actually using
it for that (the laptop in question has custom color management software, but I
think that uses standard software/GPU LUTs internally), the protocol ought to
allow for color management / gamma correction in display voltage levels, which
I believe is more flexible than what DP provides.

Have you tried to contact anyone about this? Is there anything you can say
about our chances of having this hardware supported in intel_backlight?

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