On Tue, 07 Oct 2014, Grant Diffey wrote:
so I have a really dumb question.
Why can't the controls be mapped as HCI rather than a soundcard? given there's no audio production capability here only a control capability.
Also this seems to be how they end up functioning on a modern system they get bound to pulse which remaps them to whatever's 'active'
FYI, on the old thinkpads it is the console audio volume control. It *only* affects the built-in speakers and the built-in headphone output. It does _not_ affect line-out. It does _not_ affect add-in soundcards. And it operates entirely inside the EC, with zero need of any OS assistance.
Those thinkpads don't have a separate MIC-mute button, though. I never tested them for mic-mute functionality come to think of it... the AC97 mixer in the soundcard can mute the mic, and I don't think there's an external MIC mute, because the chip they used for digital console volume control doesn't have mic channels.
Should this control control volume of my BT headset when it's active (It currently does which I find convenient but I can see an argument that it's surprising and should be bound to the phys hardware on the laptop)
Both alternatives are acceptable, as long as it doesn't lie. And on old thinkpads, you must take special action and not feed it back into the internal AC97 mixer, because it will _always_ control the console digital volume, it cannot be overriden in the older models, and the override doesn't work well because whomever wrote the EC code for the other operating modes did not test it properly.
BTW: old thinkpads don't use an ACPI interface to interact with the EC mixer, it is done by direct EC register access, and we whitelist the models where it works (the list is complete AFAIK).