jack-controls.rst (1565B)
1================== 2ALSA Jack Controls 3================== 4 5Why we need Jack kcontrols 6========================== 7 8ALSA uses kcontrols to export audio controls(switch, volume, Mux, ...) 9to user space. This means userspace applications like pulseaudio can 10switch off headphones and switch on speakers when no headphones are 11pluged in. 12 13The old ALSA jack code only created input devices for each registered 14jack. These jack input devices are not readable by userspace devices 15that run as non root. 16 17The new jack code creates embedded jack kcontrols for each jack that 18can be read by any process. 19 20This can be combined with UCM to allow userspace to route audio more 21intelligently based on jack insertion or removal events. 22 23Jack Kcontrol Internals 24======================= 25 26Each jack will have a kcontrol list, so that we can create a kcontrol 27and attach it to the jack, at jack creation stage. We can also add a 28kcontrol to an existing jack, at anytime when required. 29 30Those kcontrols will be freed automatically when the Jack is freed. 31 32How to use jack kcontrols 33========================= 34 35In order to keep compatibility, snd_jack_new() has been modified by 36adding two params: 37 38initial_kctl 39 if true, create a kcontrol and add it to the jack list. 40phantom_jack 41 Don't create a input device for phantom jacks. 42 43HDA jacks can set phantom_jack to true in order to create a phantom 44jack and set initial_kctl to true to create an initial kcontrol with 45the correct id. 46 47ASoC jacks should set initial_kctl as false. The pin name will be 48assigned as the jack kcontrol name.