1Why we need Jack kcontrols 2========================== 3 4ALSA uses kcontrols to export audio controls(switch, volume, Mux, ...) 5to user space. This means userspace applications like pulseaudio can 6switch off headphones and switch on speakers when no headphones are 7pluged in. 8 9The old ALSA jack code only created input devices for each registered 10jack. These jack input devices are not readable by userspace devices 11that run as non root. 12 13The new jack code creates embedded jack kcontrols for each jack that 14can be read by any process. 15 16This can be combined with UCM to allow userspace to route audio more 17intelligently based on jack insertion or removal events. 18 19Jack Kcontrol Internals 20======================= 21 22Each jack will have a kcontrol list, so that we can create a kcontrol 23and attach it to the jack, at jack creation stage. We can also add a 24kcontrol to an existing jack, at anytime when required. 25 26Those kcontrols will be freed automatically when the Jack is freed. 27 28How to use jack kcontrols 29========================= 30 31In order to keep compatibility, snd_jack_new() has been modified by 32adding two params :- 33 34 - @initial_kctl: if true, create a kcontrol and add it to the jack 35 list. 36 - @phantom_jack: Don't create a input device for phantom jacks. 37 38HDA jacks can set phantom_jack to true in order to create a phantom 39jack and set initial_kctl to true to create an initial kcontrol with 40the correct id. 41 42ASoC jacks should set initial_kctl as false. The pin name will be 43assigned as the jack kcontrol name. 44