ASoC: SOF: ipc4/Intel: Rename dsp_max_burst_size_in_ms to dsp_min_burst_size_in_ms

The meaning of the variable has changed with he Dynamic DeepBuffer and it
reflects the smallest burst that the host DMA does.
This can be used to set the minimum period time constraint to avoid
overshooting by the DMA burst.

Change the name and update the related code in Intel hda_dsp_pcm_open()
to reflect the revised meaning.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>

Author: ujfalusi

sound/soc/sof/intel/hda-pcm.c

@@ -29,8 +29,6 @@
 #define SDnFMT_BITS(x)	((x) << 4)
 #define SDnFMT_CHAN(x)	((x) << 0)
 
-#define HDA_MAX_PERIOD_TIME_HEADROOM	10
-
 static bool hda_always_enable_dmi_l1;
 module_param_named(always_enable_dmi_l1, hda_always_enable_dmi_l1, bool, 0444);
 MODULE_PARM_DESC(always_enable_dmi_l1, "SOF HDA always enable DMI l1");
@@ -287,36 +285,17 @@ int hda_dsp_pcm_open(struct snd_sof_dev *sdev,
 					     SNDRV_PCM_FMTBIT_S16 | SNDRV_PCM_FMTBIT_S32);
 
 	/*
-	 * The dsp_max_burst_size_in_ms is the length of the maximum burst size
+	 * The dsp_min_burst_size_in_ms is the length of the minimum 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 avoid immediate xrun by the initial burst we need to place
-	 * constraint on the period size (via PERIOD_TIME) to cover the size of
-	 * the host buffer.
-	 * We need to add headroom of max 10ms as the firmware needs time to
-	 * settle to the 1ms pacing and initially it can run faster for few
-	 * internal periods.
-	 *
-	 * On capture the DMA will transfer 1ms chunks.
+	 * Set a constraint to period time min to be at least twice as long as
+	 * the minimum burst size to avoid DMA overruns
 	 */
-	if (spcm->stream[direction].dsp_max_burst_size_in_ms) {
-		unsigned int period_time = spcm->stream[direction].dsp_max_burst_size_in_ms;
-
-		/*
-		 * add headroom over the maximum burst size to cover the time
-		 * needed for the DMA pace to settle.
-		 * Limit the headroom time to HDA_MAX_PERIOD_TIME_HEADROOM
-		 */
-		period_time += min(period_time, HDA_MAX_PERIOD_TIME_HEADROOM);
-
+	if (spcm->stream[direction].dsp_min_burst_size_in_ms)
 		snd_pcm_hw_constraint_minmax(substream->runtime,
 			SNDRV_PCM_HW_PARAM_PERIOD_TIME,
-			period_time * USEC_PER_MSEC,
+			spcm->stream[direction].dsp_min_burst_size_in_ms * USEC_PER_MSEC,
 			UINT_MAX);
-	}
 
 	/* binding pcm substream to hda stream */
 	substream->runtime->private_data = &dsp_stream->hstream;

sound/soc/sof/ipc4-topology.c

@@ -673,11 +673,11 @@ static int sof_ipc4_widget_setup_pcm(struct snd_sof_widget *swidget)
 		struct snd_sof_widget *pipe_widget = swidget->spipe->pipe_widget;
 		struct sof_ipc4_pipeline *pipeline = pipe_widget->private;
 
-		sps->dsp_max_burst_size_in_ms = pipeline->use_chain_dma ?
+		sps->dsp_min_burst_size_in_ms = pipeline->use_chain_dma ?
 			SOF_IPC4_CHAIN_DMA_BUFFER_SIZE : SOF_IPC4_MIN_DMA_BUFFER_SIZE;
 	} else {
 		/* Capture data is copied from DSP to host in 1ms bursts */
-		sps->dsp_max_burst_size_in_ms = 1;
+		sps->dsp_min_burst_size_in_ms = 1;
 	}
 
 skip_gtw_cfg:

sound/soc/sof/sof-audio.h

@@ -336,7 +336,7 @@ struct snd_sof_pcm_stream {
 	struct snd_soc_dapm_widget_list *list; /* list of connected DAPM widgets */
 	bool d0i3_compatible; /* DSP can be in D0I3 when this pcm is opened */
 	bool pause_supported; /* PCM device supports PAUSE operation */
-	unsigned int dsp_max_burst_size_in_ms; /* The maximum size of the host DMA burst in ms */
+	unsigned int dsp_min_burst_size_in_ms; /* The minimum size of the host DMA burst in ms */
 	/*
 	 * flag to indicate that the DSP pipelines should be kept
 	 * active or not while suspending the stream