[PATCH v3] ASoC: meson: aiu: fifo-spdif: soft reset the S/PDIF datapath on start/stop

[Christian Hewitt]

The I2S FIFO soft-resets its fast domain on start (AIU_RST_SOFT bit 0 +
AIU_I2S_SYNC read in aiu_fifo_i2s_trigger), mirroring the downstream
vendor driver's audio_out_i2s_enable(). The S/PDIF FIFO has no equivalent:
it only toggles the IEC958 DCU, so a stale datapath FIFO can be replayed,
producing the "machine gun noise" buffer underrun - on start when switching
outputs, and on stop when playback ends. The latter is audible on devices
with an always-on S/PDIF-fed DAC (e.g. the ES7144 on the WeTek Play2).

The vendor driver resets the IEC958 fast domain (AIU_RST_SOFT bit 2) on
both enable and disable (audio_hw_958_enable), and when reconfiguring
(audio_hw_958_reset clears AIU_958_DCU_FF_CTRL then resets). Do the same:
reset before enabling the DCU on start, and before disabling on stop.

Fixes: 6ae9ca9ce986bf ("ASoC: meson: aiu: add i2s and spdif support")
Signed-off-by: Christian Hewitt <christianshewitt@xxxxxxxxx>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@xxxxxxxxxxxxxx>

---
Changes from v2:
- Ammend description to match the change in v2
- Add Martin's reviewed-by
Changes from v1:
- Add missing fixes tag
- Trigger AIU_RST_SOFT_958_FAST before disabling DCU matching the
  stop flow in the vendor driver, as noted by Martin (tests ok)
---
 sound/soc/meson/aiu-fifo-spdif.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/sound/soc/meson/aiu-fifo-spdif.c b/sound/soc/meson/aiu-fifo-spdif.c
index e0e00ec026dc..a9861c5d6637 100644
--- a/sound/soc/meson/aiu-fifo-spdif.c
+++ b/sound/soc/meson/aiu-fifo-spdif.c
@@ -24,6 +24,7 @@
 #define AIU_MEM_IEC958_CONTROL_MODE_16BIT	BIT(7)
 #define AIU_MEM_IEC958_CONTROL_MODE_LINEAR	BIT(8)
 #define AIU_MEM_IEC958_BUF_CNTL_INIT		BIT(0)
+#define AIU_RST_SOFT_958_FAST			BIT(2)
 
 #define AIU_FIFO_SPDIF_BLOCK			8
 
@@ -68,11 +69,15 @@ static int fifo_spdif_trigger(struct snd_pcm_substream *substream, int cmd,
 	case SNDRV_PCM_TRIGGER_START:
 	case SNDRV_PCM_TRIGGER_RESUME:
 	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
+		snd_soc_component_write(component, AIU_RST_SOFT,
+					AIU_RST_SOFT_958_FAST);
 		fifo_spdif_dcu_enable(component, true);
 		break;
 	case SNDRV_PCM_TRIGGER_SUSPEND:
 	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
 	case SNDRV_PCM_TRIGGER_STOP:
+		snd_soc_component_write(component, AIU_RST_SOFT,
+					AIU_RST_SOFT_958_FAST);
 		fifo_spdif_dcu_enable(component, false);
 		break;
 	default:
-- 
2.43.0