[03/17] ASoC: SOF: Intel: hda-pcm: Use dsp_max_burst_size_in_ms to place constraint

Commit Message

Peter Ujfalusi March 21, 2024, 1:08 p.m. UTC

If the PCM have the dsp_max_burst_size_in_ms set then place a constraint
to limit the minimum buffer time to avoid xruns caused by DMA bursts
spinning on the ALSA buffer.

Cc: [e-mail] # 6.8
Signed-off-by: Peter Ujfalusi <[e-mail]>
Reviewed-by: Kai Vehmanen <[e-mail]>
Reviewed-by: Pierre-Louis Bossart <[e-mail]>
---
 sound/soc/sof/intel/hda-pcm.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

Patch

diff --git a/sound/soc/sof/intel/hda-pcm.c b/sound/soc/sof/intel/hda-pcm.c
index 18f07364d219..69fefcd1abc5 100644
--- a/sound/soc/sof/intel/hda-pcm.c
+++ b/sound/soc/sof/intel/hda-pcm.c
@@ -259,6 +259,27 @@  int hda_dsp_pcm_open(struct snd_sof_dev *sdev,
 		snd_pcm_hw_constraint_mask64(substream->runtime, SNDRV_PCM_HW_PARAM_FORMAT,
 					     SNDRV_PCM_FMTBIT_S16 | SNDRV_PCM_FMTBIT_S32);
 
+	/*
+	 * The dsp_max_burst_size_in_ms is the length of the maximum burst size
+	 * of the host DMA in the ALSA buffer.
+	 *
+	 * On playback start the DMA will transfer dsp_max_burst_size_in_ms
+	 * amount of data in one initial burst to fill up the host DMA buffer.
+	 * Consequent DMA burst sizes are shorter and their length can vary.
+	 * To make sure that userspace allocate large enough ALSA buffer we need
+	 * to place a constraint on the buffer time.
+	 *
+	 * On capture the DMA will transfer 1ms chunks.
+	 *
+	 * Exact dsp_max_burst_size_in_ms constraint is racy, so set the
+	 * constraint to a minimum of 2x dsp_max_burst_size_in_ms.
+	 */
+	if (spcm->stream[direction].dsp_max_burst_size_in_ms)
+		snd_pcm_hw_constraint_minmax(substream->runtime,
+			SNDRV_PCM_HW_PARAM_BUFFER_TIME,
+			spcm->stream[direction].dsp_max_burst_size_in_ms * USEC_PER_MSEC * 2,
+			UINT_MAX);
+
 	/* binding pcm substream to hda stream */
 	substream->runtime->private_data = &dsp_stream->hstream;
 	return 0;