ASoC: wm8960: add DAC mono mix kcontrol

In normal operation, the left and right channel digital audio data is
converted to analogue in two separate DACs. There is a mono-mix mode
where the two audio channels are mixed together digitally and then
converted to analogue using only one DAC, while the other DAC is
switched off. The mono-mix signal can be selected to appear on both
analogue output channels. The mono mix is automatically attenuated by
6dB to prevent clipping.
Signed-off-by: Zidan Wang <zidan.wang@freescale.com>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/wm8960.c

@@ -153,6 +153,7 @@ static const char *wm8960_adc_data_output_sel[] = {
 	"Left Data = Right ADC; Right Data = Right ADC",
 	"Left Data = Right ADC; Right Data = Left ADC",
 };
+static const char *wm8960_dmonomix[] = {"Stereo", "Mono"};
 
 static const struct soc_enum wm8960_enum[] = {
 	SOC_ENUM_SINGLE(WM8960_DACCTL1, 5, 4, wm8960_polarity),
@@ -162,6 +163,7 @@ static const struct soc_enum wm8960_enum[] = {
 	SOC_ENUM_SINGLE(WM8960_ALC1, 7, 4, wm8960_alcfunc),
 	SOC_ENUM_SINGLE(WM8960_ALC3, 8, 2, wm8960_alcmode),
 	SOC_ENUM_SINGLE(WM8960_ADDCTL1, 2, 4, wm8960_adc_data_output_sel),
+	SOC_ENUM_SINGLE(WM8960_ADDCTL1, 4, 2, wm8960_dmonomix),
 };
 
 static const int deemph_settings[] = { 0, 32000, 44100, 48000 };
@@ -304,6 +306,7 @@ SOC_SINGLE_TLV("Right Output Mixer RINPUT3 Volume",
 	       WM8960_ROUTMIX, 4, 7, 1, bypass_tlv),
 
 SOC_ENUM("ADC Data Output Select", wm8960_enum[6]),
+SOC_ENUM("DAC Mono Mix", wm8960_enum[7]),
 };
 
 static const struct snd_kcontrol_new wm8960_lin_boost[] = {