> But what about the display brightness? [...] In order to support the display output properly, we need a driver for Apple’s DCP coprocessor and its firmware. We’ve already talked about DCP in the past, and how cursed the interface is! Since then, Alyssa wrote a Linux kernel DRM KMS driver for DCP and Janne took over maintenance, and he’s been steadily adding features, including brightness control support.

> However, it does come with some caveats: the driver [...] may also reduce performance on some setups, since it is really meant to be used together with GPU acceleration (the simpledrm framebuffer driver has some software rendering optimizations that DCP lacks) and clients using the modern atomic-modeset and swap APIs, like Wayland compositors. It also has some limitations when used with legacy clients such as Xorg - in particular, there is no support for true VBlank interrupts, and it is unclear whether the hardware/firmware supports this at all. This breaks XFCE4’s window manager with compositing enabled. For these reasons, we are not enabling DCP by default for all users

Is there a reason they can't use the DCP driver to change display brightness without switching over to it entirely? It sounds like DCP and GPU acceleration probably ought to ship together—but IMO, changing display brightness is a must-have, in order to use a laptop comfortably in different ambient environments.