[PATCH] ASoC: fsl_sai: Force a software reset when starting in consumer mode

[Arun Raghavan <arun@arunraghavan.net>]

From: Arun Raghavan <arun@asymptotic.io>

In a setup with an external clock provider, when running the receiver
(arecord) and triggering an xrun with xrun_injection, we see a channel
swap/offset. This happens sometimes when running only the receiver, but
occurs reliably if a transmitter (aplay) is also concurrently running.

The theory is that SAI seems to lose track of frame sync during the
trigger stop -> trigger start cycle that occurs during an xrun. Doing
just a FIFO reset in this case does not suffice, and only a software
reset seems to get it back on track.

Signed-off-by: Arun Raghavan <arun@asymptotic.io>
Reported-by: Pieterjan Camerlynck <p.camerlynck@televic.com>
---
 sound/soc/fsl/fsl_sai.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/sound/soc/fsl/fsl_sai.c b/sound/soc/fsl/fsl_sai.c
index af1a168d35e3..3a5ebf32903f 100644
--- a/sound/soc/fsl/fsl_sai.c
+++ b/sound/soc/fsl/fsl_sai.c
@@ -841,6 +841,18 @@ static int fsl_sai_trigger(struct snd_pcm_substream *substream, int cmd,
 	case SNDRV_PCM_TRIGGER_START:
 	case SNDRV_PCM_TRIGGER_RESUME:
 	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
+		/*
+		 * Force a software reset if we are not the clock provider, as we
+		 * might have lost frame sync during xrun recovery.
+		 */
+		if (sai->is_consumer_mode) {
+			regmap_update_bits(sai->regmap,
+					FSL_SAI_xCSR(tx, ofs), FSL_SAI_CSR_SR,
+					FSL_SAI_CSR_SR);
+			regmap_update_bits(sai->regmap,
+					FSL_SAI_xCSR(tx, ofs), FSL_SAI_CSR_SR,
+					0);
+		}
 		regmap_update_bits(sai->regmap, FSL_SAI_xCSR(tx, ofs),
 				   FSL_SAI_CSR_FRDE, FSL_SAI_CSR_FRDE);
 
-- 
2.49.0