Hi all,
Some time ago, I asked some questions about how to handle issues with DRM drivers attempting to touch eDP while muxed away, due to implicit assumptions about eDP being permanently connected. I've proposed some changes which prevent eDP access on switched-away eDP outputs for at least i915, but now I'd like to follow up on one of the topics that was brought up during that previous conversation: namely, how to deal with systems with multiple mux devices, where it may be desirable to address the muxes independently of each other. Currently, the apple-gmux driver seems to support multiple muxes by just switching them in sync with each other, exposing only one logical mux device to the vga-switcheroo subsystem to control both physical muxes.
Since then, I've proposed a driver for a mux that is present on some upcoming notebook designs, some of which have distinct muxes for internal and external display connections [1]. I don't believe any of these systems are available publicly just yet, but it's only a matter of time before they are. During the previous discussion, I believe Daniel Vetter stated that the ability to address multiple muxes is something that could be addressed when designing a "proper" userspace API for vga-switcheroo (i.e., not debugfs), so I'd like to get the conversation started on how we could go about designing this API.