ASoC: cs42l42: Set a faster digital ramp-up rate

With the default ramp-up rate, there is a noticeable fade-in when
streams start. This can be undesirable with aggressive muting for power
saving, since the beginning of the stream is lost.

Lower the digital output ramp-up time from 8 samples per period to 2
samples per period. This still leaves some fade-in to avoid pops, but it
is a lot less noticeable and no longer feels like the stream is fading
in.

Signed-off-by: Hector Martin <[email protected]>

Author: marcan

include/sound/cs42l42.h

@@ -62,6 +62,10 @@
 #define CS42L42_INTERNAL_FS_MASK	(1 << CS42L42_INTERNAL_FS_SHIFT)
 
 #define CS42L42_SFTRAMP_RATE		(CS42L42_PAGE_10 + 0x0A)
+#define CS42L42_SFTRAMP_ASR_RATE_MASK	GENMASK(7, 4)
+#define CS42L42_SFTRAMP_ASR_RATE_SHIFT	4
+#define CS42L42_SFTRAMP_DSR_RATE_MASK	GENMASK(3, 0)
+#define CS42L42_SFTRAMP_DSR_RATE_SHIFT	0
 #define CS42L42_SLOW_START_ENABLE	(CS42L42_PAGE_10 + 0x0B)
 #define CS42L42_SLOW_START_EN_MASK	GENMASK(6, 4)
 #define CS42L42_SLOW_START_EN_SHIFT	4

sound/soc/codecs/cs42l42.c

@@ -2397,6 +2397,16 @@ int cs42l42_init(struct cs42l42_private *cs42l42)
 			(1 << CS42L42_ADC_PDN_SHIFT) |
 			(0 << CS42L42_PDN_ALL_SHIFT));
 
+	/*
+	 * Configure a faster digital ramp time, to avoid an audible
+	 * fade-in when streams start.
+	 */
+	regmap_update_bits(cs42l42->regmap, CS42L42_SFTRAMP_RATE,
+			   CS42L42_SFTRAMP_ASR_RATE_MASK |
+			   CS42L42_SFTRAMP_DSR_RATE_MASK,
+			   (10 << CS42L42_SFTRAMP_ASR_RATE_SHIFT) |
+			   (1 << CS42L42_SFTRAMP_DSR_RATE_SHIFT));
+
 	ret = cs42l42_handle_device_data(cs42l42->dev, cs42l42);
 	if (ret != 0)
 		goto err_shutdown;