ASoC: nau8825: reduce standby power consumption

Decrease internal clock frequency for power saving when standby.
But clock divider needs restore when MCLK as system clock in playback.
Signed-off-by: John Hsu <KCHSU0@nuvoton.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/nau8825.c

@@ -1132,6 +1132,9 @@ static int nau8825_configure_sysclk(struct nau8825 *nau8825, int clk_id,
 		regmap_update_bits(regmap, NAU8825_REG_CLK_DIVIDER,
 			NAU8825_CLK_SRC_MASK, NAU8825_CLK_SRC_MCLK);
 		regmap_update_bits(regmap, NAU8825_REG_FLL6, NAU8825_DCO_EN, 0);
+		/* MCLK not changed by clock tree */
+		regmap_update_bits(regmap, NAU8825_REG_CLK_DIVIDER,
+			NAU8825_CLK_MCLK_SRC_MASK, 0);
 		ret = nau8825_mclk_prepare(nau8825, freq);
 		if (ret)
 			return ret;
@@ -1142,6 +1145,13 @@ static int nau8825_configure_sysclk(struct nau8825 *nau8825, int clk_id,
 			NAU8825_DCO_EN);
 		regmap_update_bits(regmap, NAU8825_REG_CLK_DIVIDER,
 			NAU8825_CLK_SRC_MASK, NAU8825_CLK_SRC_VCO);
+		/* Decrease the VCO frequency for power saving */
+		regmap_update_bits(regmap, NAU8825_REG_CLK_DIVIDER,
+			NAU8825_CLK_MCLK_SRC_MASK, 0xf);
+		regmap_update_bits(regmap, NAU8825_REG_FLL1,
+			NAU8825_FLL_RATIO_MASK, 0x10);
+		regmap_update_bits(regmap, NAU8825_REG_FLL6,
+			NAU8825_SDM_EN, NAU8825_SDM_EN);
 		if (nau8825->mclk_freq) {
 			clk_disable_unprepare(nau8825->mclk);
 			nau8825->mclk_freq = 0;