ASoC: cs42l42: Fix mono playback

I2S always has two LRCLK phases and both CH1 and CH2 of the RX
must be enabled (corresponding to the low and high phases of LRCLK.)
The selection of the valid data channels is done by setting the DAC
CHA_SEL and CHB_SEL. CHA_SEL is always the first (left) channel,
CHB_SEL depends on the number of active channels.

Previously for mono ASP CH2 was not enabled, the result was playing
mono data would not produce any audio output.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Fixes: 621d65f ("ASoC: cs42l42: Provide finer control on playback path")
Link: https://lore.kernel.org/r/20210805161111.10410-4-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/cs42l42.c

@@ -460,8 +460,8 @@ static const struct snd_soc_dapm_widget cs42l42_dapm_widgets[] = {
 	SND_SOC_DAPM_OUTPUT("HP"),
 	SND_SOC_DAPM_DAC("DAC", NULL, CS42L42_PWR_CTL1, CS42L42_HP_PDN_SHIFT, 1),
 	SND_SOC_DAPM_MIXER("MIXER", CS42L42_PWR_CTL1, CS42L42_MIXER_PDN_SHIFT, 1, NULL, 0),
-	SND_SOC_DAPM_AIF_IN("SDIN1", NULL, 0, CS42L42_ASP_RX_DAI0_EN, CS42L42_ASP_RX0_CH1_SHIFT, 0),
-	SND_SOC_DAPM_AIF_IN("SDIN2", NULL, 1, CS42L42_ASP_RX_DAI0_EN, CS42L42_ASP_RX0_CH2_SHIFT, 0),
+	SND_SOC_DAPM_AIF_IN("SDIN1", NULL, 0, SND_SOC_NOPM, 0, 0),
+	SND_SOC_DAPM_AIF_IN("SDIN2", NULL, 1, SND_SOC_NOPM, 0, 0),
 
 	/* Playback Requirements */
 	SND_SOC_DAPM_SUPPLY("ASP DAI0", CS42L42_PWR_CTL1, CS42L42_ASP_DAI_PDN_SHIFT, 1, NULL, 0),
@@ -866,6 +866,17 @@ static int cs42l42_pcm_hw_params(struct snd_pcm_substream *substream,
 		snd_soc_component_update_bits(component, CS42L42_ASP_RX_DAI0_CH2_AP_RES,
 							 CS42L42_ASP_RX_CH_AP_MASK |
 							 CS42L42_ASP_RX_CH_RES_MASK, val);
+
+		/* Channel B comes from the last active channel */
+		snd_soc_component_update_bits(component, CS42L42_SP_RX_CH_SEL,
+					      CS42L42_SP_RX_CHB_SEL_MASK,
+					      (channels - 1) << CS42L42_SP_RX_CHB_SEL_SHIFT);
+
+		/* Both LRCLK slots must be enabled */
+		snd_soc_component_update_bits(component, CS42L42_ASP_RX_DAI0_EN,
+					      CS42L42_ASP_RX0_CH_EN_MASK,
+					      BIT(CS42L42_ASP_RX0_CH1_SHIFT) |
+					      BIT(CS42L42_ASP_RX0_CH2_SHIFT));
 		break;
 	default:
 		break;

sound/soc/codecs/cs42l42.h

@@ -653,6 +653,8 @@
 
 /* Page 0x25 Audio Port Registers */
 #define CS42L42_SP_RX_CH_SEL		(CS42L42_PAGE_25 + 0x01)
+#define CS42L42_SP_RX_CHB_SEL_SHIFT	2
+#define CS42L42_SP_RX_CHB_SEL_MASK	(3 << CS42L42_SP_RX_CHB_SEL_SHIFT)
 
 #define CS42L42_SP_RX_ISOC_CTL		(CS42L42_PAGE_25 + 0x02)
 #define CS42L42_SP_RX_RSYNC_SHIFT	6