| Jie Yang | 12e180a | 2015-04-27 21:21:02 +0800 | [diff] [blame] | 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. |