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authorTakashi Iwai <tiwai@suse.de>2016-11-10 13:10:35 +0300
committerTakashi Iwai <tiwai@suse.de>2016-11-10 20:09:31 +0300
commitdf3a57105c04a7bfe0874316a9e6ec968c35a6f5 (patch)
tree0b3d0bafeef9e415ac60359672e4bd4fd20c5fd8 /Documentation/sound/designs
parent20a1d0f44d9447a68c387a2f561db4720302fb7c (diff)
downloadlinux-df3a57105c04a7bfe0874316a9e6ec968c35a6f5.tar.xz
ALSA: doc: ReSTize Jack-Controls.txt
A simple conversion from a plain text file. Put to designs subdirectory. Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'Documentation/sound/designs')
-rw-r--r--Documentation/sound/designs/index.rst1
-rw-r--r--Documentation/sound/designs/jack-controls.rst48
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diff --git a/Documentation/sound/designs/index.rst b/Documentation/sound/designs/index.rst
index 798b1a44bbbd..04dcdae3e4f2 100644
--- a/Documentation/sound/designs/index.rst
+++ b/Documentation/sound/designs/index.rst
@@ -8,6 +8,7 @@ Designs and Implementations
channel-mapping-api
compress-offload
timestamping
+ jack-controls
procfile
powersave
oss-emulation
diff --git a/Documentation/sound/designs/jack-controls.rst b/Documentation/sound/designs/jack-controls.rst
new file mode 100644
index 000000000000..ae25b1531bb0
--- /dev/null
+++ b/Documentation/sound/designs/jack-controls.rst
@@ -0,0 +1,48 @@
+==================
+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.