| ================== |
| ALSA Jack Controls |
| ================== |
| |
| Why we need Jack kcontrols |
| ========================== |
| |
| ALSA uses kcontrols to export audio controls(switch, volume, Mux, ...) |
| to user space. This means userspace applications like pulseaudio can |
| switch off headphones and switch on speakers when no headphones are |
| pluged in. |
| |
| The old ALSA jack code only created input devices for each registered |
| jack. These jack input devices are not readable by userspace devices |
| that run as non root. |
| |
| The new jack code creates embedded jack kcontrols for each jack that |
| can be read by any process. |
| |
| This can be combined with UCM to allow userspace to route audio more |
| intelligently based on jack insertion or removal events. |
| |
| Jack Kcontrol Internals |
| ======================= |
| |
| Each jack will have a kcontrol list, so that we can create a kcontrol |
| and attach it to the jack, at jack creation stage. We can also add a |
| kcontrol to an existing jack, at anytime when required. |
| |
| Those kcontrols will be freed automatically when the Jack is freed. |
| |
| How to use jack kcontrols |
| ========================= |
| |
| In order to keep compatibility, snd_jack_new() has been modified by |
| adding two params: |
| |
| initial_kctl |
| if true, create a kcontrol and add it to the jack list. |
| phantom_jack |
| Don't create a input device for phantom jacks. |
| |
| HDA jacks can set phantom_jack to true in order to create a phantom |
| jack and set initial_kctl to true to create an initial kcontrol with |
| the correct id. |
| |
| ASoC jacks should set initial_kctl as false. The pin name will be |
| assigned as the jack kcontrol name. |
