ALSA: hda/realtek - Add LED class support for micmute LED

Currently DMIC controls micmute LED via "audio mute LED trigger".

However, unlike Dell and Lenovo platforms, HP platforms don't provide a
way to control micmute LED via ACPI, it's controlled by HDA codec
instead.

So let's register an LED class for micmute so other subsystems like DMIC
can facilitate the codec-controlled LED.
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Link: https://lore.kernel.org/r/20200430135209.14703-1-kai.heng.feng@canonical.comSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/patch_realtek.c

@@ -17,6 +17,7 @@
 #include <linux/dmi.h>
 #include <linux/module.h>
 #include <linux/input.h>
+#include <linux/leds.h>
 #include <sound/core.h>
 #include <sound/jack.h>
 #include <sound/hda_codec.h>
@@ -4103,6 +4104,26 @@ static void alc_gpio_micmute_update(struct hda_codec *codec)
 			    spec->gen.micmute_led.led_value);
 }
 
+#if IS_REACHABLE(CONFIG_LEDS_TRIGGER_AUDIO)
+static int micmute_led_set(struct led_classdev *led_cdev,
+			   enum led_brightness brightness)
+{
+	struct hda_codec *codec = dev_to_hda_codec(led_cdev->dev->parent);
+	struct alc_spec *spec = codec->spec;
+
+	alc_update_gpio_led(codec, spec->gpio_mic_led_mask,
+			    spec->micmute_led_polarity, !!brightness);
+	return 0;
+}
+
+static struct led_classdev micmute_led_cdev = {
+	.name = "hda::micmute",
+	.max_brightness = 1,
+	.brightness_set_blocking = micmute_led_set,
+	.default_trigger = "audio-micmute",
+};
+#endif
+
 /* setup mute and mic-mute GPIO bits, add hooks appropriately */
 static void alc_fixup_hp_gpio_led(struct hda_codec *codec,
 				  int action,
@@ -4110,6 +4131,7 @@ static void alc_fixup_hp_gpio_led(struct hda_codec *codec,
 				  unsigned int micmute_mask)
 {
 	struct alc_spec *spec = codec->spec;
+	int err;
 
 	alc_fixup_gpio(codec, action, mute_mask | micmute_mask);
 
@@ -4122,6 +4144,13 @@ static void alc_fixup_hp_gpio_led(struct hda_codec *codec,
 	if (micmute_mask) {
 		spec->gpio_mic_led_mask = micmute_mask;
 		snd_hda_gen_add_micmute_led(codec, alc_gpio_micmute_update);
+
+#if IS_REACHABLE(CONFIG_LEDS_TRIGGER_AUDIO)
+		micmute_led_cdev.brightness = ledtrig_audio_get(LED_AUDIO_MICMUTE);
+		err = devm_led_classdev_register(&codec->core.dev, &micmute_led_cdev);
+		if (err)
+			codec_warn(codec, "failed to register micmute LED\n");
+#endif
 	}
 }