[PATCH v4 0/6] ALSA: control - add generic LED API

[Jaroslav Kysela <perex@perex.cz>]

This patchset tries to resolve the diversity in the audio LED
control among the ALSA drivers. A new control layer registration
is introduced which allows to run additional operations on
top of the elementary ALSA sound controls.

A new control access group (three bits in the access flags)
was introduced to carry the LED group information for
the sound controls. The low-level sound drivers can just
mark those controls using this access group. This information
is not exported to the user space, but user space can
manage the LED sound control associations through sysfs
(last patch) per Mark's request. It makes things fully
configurable in the kernel and user space (UCM).

The actual state ('route') evaluation is really easy
(the minimal value check for all channels / controls / cards).
If there's more complicated logic for a given hardware,
the card driver may eventually export a new read-only
sound control for the LED group and do the logic itself.

The new LED trigger control code is completely separated
and possibly optional (there's no symbol dependency).
The full code separation allows eventually to move this
LED trigger control to the user space in future.
Actually it replaces the already present functionality
in the kernel space (HDA drivers) and allows a quick adoption
for the recent hardware (ASoC codecs including SoundWire).

# lsmod | grep snd_ctl_led
snd_ctl_led            24576  0

The sound driver implementation is really easy:

1) call snd_ctl_led_request() when control LED layer should be
   automatically activated
   / it calls module_request("snd-ctl-led") on demand /
2) mark all related kcontrols with
	SNDRV_CTL_ELEM_ACCESS_SPK_LED or
	SNDRV_CTL_ELEM_ACCESS_MIC_LED

v4 changes:
  - the LED access flags are private to kernel now (no user space
    API change)
  - fixes (kctl management, sysfs cleanup)
  - add the sysfs LED marking kcontrol management
    - https://lore.kernel.org/alsa-devel/28fffebd-1ce9-7480-0f2f-ed8369abddf1@perex.cz/
v3 changes:
  - reorder the controls_rwsem use to fix the remaining mutex issue
    card->controls_rwsem <-> snd_ctl_layer_rwsem
v2 changes:
  - fix the locking - remove the controls_rwsem read lock
    in the element get (the consistency is already protected
    with the global snd_ctl_led_mutex and possible partial
    value writes are catched with the next value change
    notification callback)
  - rename state to brightness and show the brightness
    unsigned integer value instead the text on/off string
    (sync with the LED core routines)
  - remove snd_ctl_led_hello() function (CI warning)
  - make snd_ctl_led_get_by_access() function static (CI warning)
  - move snd_ctl_layer_rwsem lock before the registraction
    callback call in snd_ctl_register_layer() - optimization
v1:
  - https://lore.kernel.org/alsa-devel/20210211111400.1131020-1-perex@perex.cz/
Original RFC:
  - https://lore.kernel.org/alsa-devel/20210207201157.869972-1-perex@perex.cz/

Cc: Hans de Goede <hdegoede@redhat.com>

Jaroslav Kysela (6):
  ALSA: control - introduce snd_ctl_notify_one() helper
  ALSA: control - add layer registration routines
  ALSA: control - add generic LED trigger module as the new control
    layer
  ALSA: HDA - remove the custom implementation for the audio LED trigger
  ALSA: control - add sysfs support to the LED trigger module
  ALSA: led control - add sysfs kcontrol LED marking layer

 include/sound/control.h         |  35 +-
 sound/core/Kconfig              |   6 +
 sound/core/Makefile             |   2 +
 sound/core/control.c            | 182 ++++++--
 sound/core/control_led.c        | 770 ++++++++++++++++++++++++++++++++
 sound/pci/hda/Kconfig           |   4 +-
 sound/pci/hda/hda_codec.c       |  69 +--
 sound/pci/hda/hda_generic.c     | 162 ++-----
 sound/pci/hda/hda_generic.h     |  15 +-
 sound/pci/hda/hda_local.h       |  16 +-
 sound/pci/hda/patch_ca0132.c    |   4 +-
 sound/pci/hda/patch_realtek.c   |   2 +-
 sound/pci/hda/patch_sigmatel.c  |   6 +-
 sound/pci/hda/thinkpad_helper.c |   2 +-
 14 files changed, 1011 insertions(+), 264 deletions(-)
 create mode 100644 sound/core/control_led.c

-- 
2.29.2