Emulator

Even then, it's very likely a super small fraction compared to the entire Wii library. Having to manually go back and forth enabling/disabling the integrated GBAs whenever switching between GC and Wii games just so a few Wii homebrews can interact with the mGBA instances seems very counterintuitive.

What about adding a checkbox to the controller settings window and starting mGBA instances in Wii mode only when that checkbox is marked? Something like "Connect GBAs in Wii mode"? That way, mGBA instances wouldn't be started by default in Wii mode (arguably the most common use case) but the option would still be there for anyone that wants to run those homebrews...

How is the problem of integrated GBAs starting when playing a Wii game that doesn't support them any different from the problem of integrated GBAs starting when playing a GameCube game that doesn't support them? Adding a checkbox for just Wii games wouldn't be a complete solution, and combined with the fact that there is Wii homebrew that can connect to GBAs, I don't think trying to special-case the Wii makes sense.

I just tested this on console, I believe Dolphin is handling this correctly. If a GBA connected via the GameCube Link Cable is plugged into Controller Slot 1 and I boot up Super Mario Galaxy, it sits on the BIOS screen just like the Integrated GBA option.

Although I've initially considered only Wii games when opening this issue, the point remains: the majority of the GC library and the entire Wii library (apart from some homebrews) does not support GBA connectivity, so we shouldn't be starting GBA instances by default in scenarios we know they can't be used. It's just wasteful, and that can impact the performance in lower end PCs and Android devices, especially if you've all 4 ports set as integrated GBAs.

About the checkbox, make it apply to all games, independent of being a GC or Wii title, and manually override it so it's always enabled on the Game INI of the supported games. This is just one possible UX approach I can think right now (and very likely not the best one)...

I think adding complexity in that way is just a bad idea, especially if we start getting things like mods to games and if there are games with incomplete features that are finished with cheats/hacks. There's also the case where maybe you want to have a GBA window open alongside Dolphin while you're playing a different game grinding Pokemon or something and you're too lazy to start up mGBA or VBA-M proper. Or you just want it already configured for the savefile that the Integrated GBA would use.

I honestly don't know, I've been using the feature for a while and this never crossed my mind. Because the GBAs run on dedicated threads, I'm not sure they'd even cause an issue on Android.

And there is also the matter that just because a game supports connecting to a GBA doesn't necessarily mean it supports GBAs in the game modes you care about playing. Take Animal Crossing or Sonic Adventure 2, for instance.

That's true. I just think that the people who use this feature will turn it on when they need it. Most GC games that don't need it you'll turn it off, since you'd be using the other controller ports anyway.

The Wii thing is slightly more interesting, but if you hear four GBAs blaring at once I think you'll understand you want to turn them off.

¯\_(ツ)_/¯