ASoC: Actively manage the DC servo for WM8903

Save a little extra power by enabling the DC servo offset correction
for the output channels only when the relevant channels are enabled.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

diff --git a/sound/soc/codecs/wm8903.c b/sound/soc/codecs/wm8903.c
index de0a585..0bab5c6 100644 (file)
--- a/sound/soc/codecs/wm8903.c
+++ b/sound/soc/codecs/wm8903.c
@@ -392,14 +392,18 @@ static int wm8903_output_event(struct snd_soc_dapm_widget *w,
        struct snd_soc_codec *codec = w->codec;
        u16 val;
        u16 reg;
+       u16 dcs_reg;
+       u16 dcs_bit;
        int shift;
 
        switch (w->reg) {
        case WM8903_POWER_MANAGEMENT_2:
                reg = WM8903_ANALOGUE_HP_0;
+               dcs_bit = 0 + w->shift;
                break;
        case WM8903_POWER_MANAGEMENT_3:
                reg = WM8903_ANALOGUE_LINEOUT_0;
+               dcs_bit = 2 + w->shift;
                break;
        default:
                BUG();
@@ -439,6 +443,11 @@ static int wm8903_output_event(struct snd_soc_dapm_widget *w,
                val |= (WM8903_OUTPUT_OUT << shift);
                wm8903_write(codec, reg, val);
 
+               /* Enable the DC servo */
+               dcs_reg = wm8903_read(codec, WM8903_DC_SERVO_0);
+               dcs_reg |= dcs_bit;
+               wm8903_write(codec, WM8903_DC_SERVO_0, dcs_reg);
+
                /* Remove the short */
                val |= (WM8903_OUTPUT_SHORT << shift);
                wm8903_write(codec, reg, val);
@@ -451,6 +460,11 @@ static int wm8903_output_event(struct snd_soc_dapm_widget *w,
                val &= ~(WM8903_OUTPUT_SHORT << shift);
                wm8903_write(codec, reg, val);
 
+               /* Disable the DC servo */
+               dcs_reg = wm8903_read(codec, WM8903_DC_SERVO_0);
+               dcs_reg &= ~dcs_bit;
+               wm8903_write(codec, WM8903_DC_SERVO_0, dcs_reg);
+
                /* Then disable the intermediate and output stages */
                val &= ~((WM8903_OUTPUT_OUT | WM8903_OUTPUT_INT |
                          WM8903_OUTPUT_IN) << shift);