[PATCH v5 02/31] drm/i915: Don't register backlight when another backlight should be used (v2)

[Matthew Garrett]

On Tue, Oct 25, 2022 at 08:50:54PM +0200, Hans de Goede wrote:

> That is a valid point, but keep in mind that this is only used on ACPI
> platforms and then only on devices with a builtin LCD panel and then
> only by GPU drivers which actually call acpi_video_get_backlight_type(),
> so e.g. not by all the ARM specific display drivers.
> 
> So I believe that Chromebooks quite likely are the only devices with
> this issue.

My laptop is, uh, weird, but it falls into this category.
 
> > I think for this to work correctly you need to have 
> > the infrastructure be aware of whether or not a vendor interface exists, 
> > which means having to handle cleanup if a vendor-specific module gets 
> > loaded later.
> 
> Getting rid of the whole ping-ponging of which backlight drivers
> get loaded during boot was actually one of the goals of the rework
> which landed in 6.1 this actually allowed us to remove some quirks
> because some hw/firmware did not like us changing our mind and
> switching backlight interfaces after first poking another one.
> So we definitely don't want to go back to the ping-pong thing.

Defaulting to native but then having a vendor driver be able to disable 
native drivers seems easiest? It shouldn't be a regression over the 
previous state of affairs since both drivers were being loaded already.