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