leds: trigger: Introduce audio mute LED trigger

This patch adds a new LED trigger for coupling the audio mixer change
with the LED on laptops or other devices.  Currently there are two
trigger types, "audio-mute" and "audio-micmute".

The audio driver triggers the LED brightness change via
ledtrig_audio_set() call with the proper type (either mute or
mic-mute).  OTOH, the consumers may call ledtrig_audio_get() for the
initial brightness value that may have been set by the audio driver
beforehand.

This new stuff will be used by HD-audio codec driver and some platform
drivers (thinkpad_acpi and dell-laptop, also upcoming huawei-wmi).

Acked-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

drivers/leds/trigger/Kconfig

@@ -136,4 +136,11 @@ config LEDS_TRIGGER_PATTERN
 	  which is a series of tuples, of brightness and duration (ms).
 	  If unsure, say N
 
+config LEDS_TRIGGER_AUDIO
+	tristate "Audio Mute LED Trigger"
+	help
+	  This allows LEDs to be controlled by audio drivers for following
+	  the audio mute and mic-mute changes.
+	  If unsure, say N
+
 endif # LEDS_TRIGGERS

drivers/leds/trigger/Makefile

@@ -14,3 +14,4 @@ obj-$(CONFIG_LEDS_TRIGGER_CAMERA)	+= ledtrig-camera.o
 obj-$(CONFIG_LEDS_TRIGGER_PANIC)	+= ledtrig-panic.o
 obj-$(CONFIG_LEDS_TRIGGER_NETDEV)	+= ledtrig-netdev.o
 obj-$(CONFIG_LEDS_TRIGGER_PATTERN)	+= ledtrig-pattern.o
+obj-$(CONFIG_LEDS_TRIGGER_AUDIO)	+= ledtrig-audio.o

drivers/leds/trigger/ledtrig-audio.c

@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Audio Mute LED trigger
+//
+
+#include <linux/kernel.h>
+#include <linux/leds.h>
+#include <linux/module.h>
+
+static struct led_trigger *ledtrig_audio[NUM_AUDIO_LEDS];
+static enum led_brightness audio_state[NUM_AUDIO_LEDS];
+
+enum led_brightness ledtrig_audio_get(enum led_audio type)
+{
+	return audio_state[type];
+}
+EXPORT_SYMBOL_GPL(ledtrig_audio_get);
+
+void ledtrig_audio_set(enum led_audio type, enum led_brightness state)
+{
+	audio_state[type] = state;
+	led_trigger_event(ledtrig_audio[type], state);
+}
+EXPORT_SYMBOL_GPL(ledtrig_audio_set);
+
+static int __init ledtrig_audio_init(void)
+{
+	led_trigger_register_simple("audio-mute",
+				    &ledtrig_audio[LED_AUDIO_MUTE]);
+	led_trigger_register_simple("audio-micmute",
+				    &ledtrig_audio[LED_AUDIO_MICMUTE]);
+	return 0;
+}
+module_init(ledtrig_audio_init);
+
+static void __exit ledtrig_audio_exit(void)
+{
+	led_trigger_unregister_simple(ledtrig_audio[LED_AUDIO_MUTE]);
+	led_trigger_unregister_simple(ledtrig_audio[LED_AUDIO_MICMUTE]);
+}
+module_exit(ledtrig_audio_exit);
+
+MODULE_DESCRIPTION("LED trigger for audio mute control");
+MODULE_LICENSE("GPL v2");

include/linux/leds.h

@@ -487,4 +487,24 @@ struct led_pattern {
 	int brightness;
 };
 
+enum led_audio {
+	LED_AUDIO_MUTE,		/* master mute LED */
+	LED_AUDIO_MICMUTE,	/* mic mute LED */
+	NUM_AUDIO_LEDS
+};
+
+#if IS_ENABLED(CONFIG_LEDS_TRIGGER_AUDIO)
+enum led_brightness ledtrig_audio_get(enum led_audio type);
+void ledtrig_audio_set(enum led_audio type, enum led_brightness state);
+#else
+static inline enum led_brightness ledtrig_audio_get(enum led_audio type)
+{
+	return LED_OFF;
+}
+static inline void ledtrig_audio_set(enum led_audio type,
+				     enum led_brightness state)
+{
+}
+#endif
+
 #endif		/* __LINUX_LEDS_H_INCLUDED */