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authorJosé Pekkarinen <jose.pekkarinen@nokia.com>2016-04-11 10:41:07 +0300
committerJosé Pekkarinen <jose.pekkarinen@nokia.com>2016-04-13 08:17:18 +0300
commite09b41010ba33a20a87472ee821fa407a5b8da36 (patch)
treed10dc367189862e7ca5c592f033dc3726e1df4e3 /kernel/Documentation/sound/alsa/Jack-Controls.txt
parentf93b97fd65072de626c074dbe099a1fff05ce060 (diff)
These changes are the raw update to linux-4.4.6-rt14. Kernel sources
are taken from kernel.org, and rt patch from the rt wiki download page. During the rebasing, the following patch collided: Force tick interrupt and get rid of softirq magic(I70131fb85). Collisions have been removed because its logic was found on the source already. Change-Id: I7f57a4081d9deaa0d9ccfc41a6c8daccdee3b769 Signed-off-by: José Pekkarinen <jose.pekkarinen@nokia.com>
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+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.