[ALSA] ice1724 - Add PCM Playback Switch to Revo 7.1

This patch adds the support of mute for front channels of M-Audio
Revolution 7.1 (the DAC AK4381 features a mute bit).

Signed-off-by: Pavel Hofman <[e-mail]>
Signed-off-by: Takashi Iwai <[e-mail]>
Signed-off-by: Jaroslav Kysela <[e-mail]>

include/sound/ak4xxx-adda.h

···
 struct snd_akm4xxx_dac_channel {
 	char *name;		/* mixer volume name */
 	unsigned int num_channels;
+	char *switch_name;		/* mixer switch*/
 };
 
 /* ADC labels and channels */

sound/i2c/other/ak4xxx-adda.c

···
 	int addr = AK_GET_ADDR(kcontrol->private_value);
 	int shift = AK_GET_SHIFT(kcontrol->private_value);
 	int invert = AK_GET_INVERT(kcontrol->private_value);
-	unsigned char val = snd_akm4xxx_get(ak, chip, addr);
-
+	/* we observe the (1<<shift) bit only */
+	unsigned char val = snd_akm4xxx_get(ak, chip, addr) & (1<<shift);
 	if (invert)
 		val = ! val;
 	ucontrol->value.integer.value[0] = (val & (1<<shift)) != 0;
···
 
 	mixer_ch = 0;
 	for (idx = 0; idx < ak->num_dacs; ) {
+		/* mute control for Revolution 7.1 - AK4381 */
+		if (ak->type == SND_AK4381 
+				&&  ak->dac_info[mixer_ch].switch_name) {
+			memset(&knew, 0, sizeof(knew));
+			knew.iface = SNDRV_CTL_ELEM_IFACE_MIXER;
+			knew.count = 1;
+			knew.access = SNDRV_CTL_ELEM_ACCESS_READWRITE;
+			knew.name = ak->dac_info[mixer_ch].switch_name;
+			knew.info = ak4xxx_switch_info;
+			knew.get = ak4xxx_switch_get;
+			knew.put = ak4xxx_switch_put;
+			knew.access = 0;
+			/* register 1, bit 0 (SMUTE): 0 = normal operation,
+			   1 = mute */
+			knew.private_value =
+				AK_COMPOSE(idx/2, 1, 0, 0) | AK_INVERT;
+			err = snd_ctl_add(ak->card, snd_ctl_new1(&knew, ak));
+			if (err < 0)
+				return err;
+		}
 		memset(&knew, 0, sizeof(knew));
 		if (! ak->dac_info || ! ak->dac_info[mixer_ch].name) {
 			knew.name = "DAC Volume";

sound/pci/ice1712/revo.c

···
 #define AK_DAC(xname,xch) { .name = xname, .num_channels = xch }
 
 static const struct snd_akm4xxx_dac_channel revo71_front[] = {
-	AK_DAC("PCM Playback Volume", 2)
+	{
+		.name = "PCM Playback Volume",
+		.num_channels = 2,
+		/* front channels DAC supports muting */
+		.switch_name = "PCM Playback Switch",
+	},
 };
 
 static const struct snd_akm4xxx_dac_channel revo71_surround[] = {