ALSA: jack: implement software jack injection via debugfs

This change adds audio jack injection feature through debugfs, with
this feature, we could validate alsa userspace changes by injecting
plugin or plugout events to the non-phantom audio jacks.

With this change, the sound core will build the folders
$debugfs_mount_dir/sound/cardN if SND_DEBUG and DEBUG_FS are enabled.
And if users also enable the SND_JACK_INJECTION_DEBUG, the jack
injection nodes will be built in the folder cardN like below:

$tree $debugfs_mount_dir/sound
$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 nodes kctl_id, mask_bits, status and type are read-only, users
could check jack or jack_kctl's information through them.

The nodes sw_inject_enable and jackin_inject are directly used for
injection. The sw_inject_enable is read-write, users could check if
software injection is enabled or not on this jack, and users could
echo 1 or 0 to enable or disable software injection on this jack. Once
the injection is enabled, the jack will not change by hardware events
anymore, once the injection is disabled, the jack will restore the
last reported hardware events to the jack. The jackin_inject is
write-only, if the injection is enabled, users could echo 1 or 0 to
this node to inject plugin or plugout events to this jack.

For the detailed usage information on these nodes, please refer to
Documentation/sound/designs/jack-injection.rst.

Reviewed-by: Takashi Iwai <tiwai@suse.de>
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Reviewed-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Signed-off-by: Hui Wang <hui.wang@canonical.com>
Link: https://lore.kernel.org/r/20210127085639.74954-2-hui.wang@canonical.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

2 files changed, 167 insertions, 0 deletions

diff --git a/Documentation/sound/designs/index.rst b/Documentation/sound/designs/index.rst
index f0749943ccb2..1eb08e7bae52 100644
--- a/Documentation/sound/designs/index.rst
+++ b/Documentation/sound/designs/index.rst
@@ -14,3 +14,4 @@ Designs and Implementations
    powersave
    oss-emulation
    seq-oss
+   jack-injection
diff --git a/Documentation/sound/designs/jack-injection.rst b/Documentation/sound/designs/jack-injection.rst
new file mode 100644
index 000000000000..f9790521523e
--- /dev/null
+++ b/Documentation/sound/designs/jack-injection.rst
@@ -0,0 +1,166 @@
+============================
+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