Based on kernel version 4.9. Page generated on 2016-12-21 14:37 EST.
1 Why we need Jack kcontrols 2 ========================== 3 4 ALSA uses kcontrols to export audio controls(switch, volume, Mux, ...) 5 to user space. This means userspace applications like pulseaudio can 6 switch off headphones and switch on speakers when no headphones are 7 pluged in. 8 9 The old ALSA jack code only created input devices for each registered 10 jack. These jack input devices are not readable by userspace devices 11 that run as non root. 12 13 The new jack code creates embedded jack kcontrols for each jack that 14 can be read by any process. 15 16 This can be combined with UCM to allow userspace to route audio more 17 intelligently based on jack insertion or removal events. 18 19 Jack Kcontrol Internals 20 ======================= 21 22 Each jack will have a kcontrol list, so that we can create a kcontrol 23 and attach it to the jack, at jack creation stage. We can also add a 24 kcontrol to an existing jack, at anytime when required. 25 26 Those kcontrols will be freed automatically when the Jack is freed. 27 28 How to use jack kcontrols 29 ========================= 30 31 In order to keep compatibility, snd_jack_new() has been modified by 32 adding 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 38 HDA jacks can set phantom_jack to true in order to create a phantom 39 jack and set initial_kctl to true to create an initial kcontrol with 40 the correct id. 41 42 ASoC jacks should set initial_kctl as false. The pin name will be 43 assigned as the jack kcontrol name.