linux/linux-5.18.11/Documentation/sound/designs/jack-injection.rst

============================
ALSA Jack Software Injection
============================

Simple Introduction On Jack Injection
=====================================

Here jack injection means users could inject plugin or plugout events
to the audio jacks through debugfs interface, it is helpful to
validate ALSA userspace changes. For example, we change the audio
profile switching code in the pulseaudio, and we want to verify if the
change works as expected and if the change introduce the regression,
in this case, we could inject plugin or plugout events to an audio
jack or to some audio jacks, we don't need to physically access the
machine and plug/unplug physical devices to the audio jack.

In this design, an audio jack doesn't equal to a physical audio jack.
Sometimes a physical audio jack contains multi functions, and the
ALSA driver creates multi ``jack_kctl`` for a ``snd_jack``, here the
``snd_jack`` represents a physical audio jack and the ``jack_kctl``
represents a function, for example a physical jack has two functions:
headphone and mic_in, the ALSA ASoC driver will build 2 ``jack_kctl``
for this jack. The jack injection is implemented based on the
``jack_kctl`` instead of ``snd_jack``.

To inject events to audio jacks, we need to enable the jack injection
via ``sw_inject_enable`` first, once it is enabled, this jack will not
change the state by hardware events anymore, we could inject plugin or
plugout events via ``jackin_inject`` and check the jack state via
``status``, after we finish our test, we need to disable the jack
injection via ``sw_inject_enable`` too, once it is disabled, the jack
state will be restored according to the last reported hardware events
and will change by future hardware events.

The Layout of Jack Injection Interface
======================================

If users enable the SND_JACK_INJECTION_DEBUG in the kernel, the audio
jack injection interface will be created as below:
::

   $debugfs_mount_dir/sound
   |-- card0
   |-- |-- HDMI_DP_pcm_10_Jack
   |-- |-- |-- jackin_inject
   |-- |-- |-- kctl_id
   |-- |-- |-- mask_bits
   |-- |-- |-- status
   |-- |-- |-- sw_inject_enable
   |-- |-- |-- type
   ...
   |-- |-- HDMI_DP_pcm_9_Jack
   |--     |-- jackin_inject
   |--     |-- kctl_id
   |--     |-- mask_bits
   |--     |-- status
   |--     |-- sw_inject_enable
   |--     |-- type
   |-- card1
       |-- HDMI_DP_pcm_5_Jack
       |-- |-- jackin_inject
       |-- |-- kctl_id
       |-- |-- mask_bits
       |-- |-- status
       |-- |-- sw_inject_enable
       |-- |-- type
       ...
       |-- Headphone_Jack
       |-- |-- jackin_inject
       |-- |-- kctl_id
       |-- |-- mask_bits
       |-- |-- status
       |-- |-- sw_inject_enable
       |-- |-- type
       |-- Headset_Mic_Jack
           |-- jackin_inject
           |-- kctl_id
           |-- mask_bits
           |-- status
           |-- sw_inject_enable
           |-- type

The Explanation Of The Nodes
======================================

kctl_id
  read-only, get jack_kctl->kctl's id
  ::

     sound/card1/Headphone_Jack# cat kctl_id
     Headphone Jack

mask_bits
  read-only, get jack_kctl's supported events mask_bits
  ::

     sound/card1/Headphone_Jack# cat mask_bits
     0x0001 HEADPHONE(0x0001)

status
  read-only, get jack_kctl's current status

- headphone unplugged:

  ::

     sound/card1/Headphone_Jack# cat status
     Unplugged

- headphone plugged:

  ::

     sound/card1/Headphone_Jack# cat status
     Plugged

type
  read-only, get snd_jack's supported events from type (all supported events on the physical audio jack)
  ::

     sound/card1/Headphone_Jack# cat type
     0x7803 HEADPHONE(0x0001) MICROPHONE(0x0002) BTN_3(0x0800) BTN_2(0x1000) BTN_1(0x2000) BTN_0(0x4000)

sw_inject_enable
  read-write, enable or disable injection

- injection disabled:

  ::

     sound/card1/Headphone_Jack# cat sw_inject_enable
     Jack: Headphone Jack		Inject Enabled: 0

- injection enabled:

  ::

     sound/card1/Headphone_Jack# cat sw_inject_enable
     Jack: Headphone Jack		Inject Enabled: 1

- to enable jack injection:

  ::

     sound/card1/Headphone_Jack# echo 1 > sw_inject_enable

- to disable jack injection:

  ::

     sound/card1/Headphone_Jack# echo 0 > sw_inject_enable

jackin_inject
  write-only, inject plugin or plugout

- to inject plugin:

  ::

     sound/card1/Headphone_Jack# echo 1 > jackin_inject

- to inject plugout:

  ::

     sound/card1/Headphone_Jack# echo 0 > jackin_inject