ASoC: fsl_asrc_m2m: Add option to start ASRC before DMA device for M2M

There is a limitation on i.MX952 that dma request is not cleared at the
end of conversion with dma slave mode. Which causes sample is dropped
from the input fifo on the second time if dma is triggered before the
client device and EDMA may copy wrong data from output fifo as the output
fifo is not ready in the beginning.

The solution is to trigger asrc before dma on i.MX952, and add delay to
wait output data is generated then start the EDMA for output, otherwise
the m2m function has noise issues.

So add an option to start ASRC first for M2M before ASRC is enabled on
i.MX952.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Reviewed-by: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260206014805.3897764-3-shengjiu.wang@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: TE-N-ShengjiuWang

sound/soc/fsl/fsl_asrc.c

@@ -1078,6 +1078,26 @@ static unsigned int fsl_asrc_get_output_fifo_size(struct fsl_asrc_pair *pair)
 	return val >> ASRFSTi_OUTPUT_FIFO_SHIFT;
 }
 
+static bool fsl_asrc_m2m_output_ready(struct fsl_asrc_pair *pair)
+{
+	struct fsl_asrc *asrc = pair->asrc;
+	enum asrc_pair_index index = pair->index;
+	u32 val;
+	int ret;
+
+	/* Check output fifo status if it exceeds the watermark. */
+	ret = regmap_read_poll_timeout(asrc->regmap, REG_ASRFST(index), val,
+				       (ASRFSTi_OUTPUT_FIFO_FILL(val) >= ASRC_M2M_OUTPUTFIFO_WML),
+				       1, 1000);
+
+	if (ret) {
+		pair_warn("output is not ready\n");
+		return false;
+	}
+
+	return true;
+}
+
 static int fsl_asrc_m2m_prepare(struct fsl_asrc_pair *pair)
 {
 	struct fsl_asrc_pair_priv *pair_priv = pair->private;
@@ -1275,6 +1295,7 @@ static int fsl_asrc_probe(struct platform_device *pdev)
 
 	asrc_priv->soc = of_device_get_match_data(&pdev->dev);
 	asrc->use_edma = asrc_priv->soc->use_edma;
+	asrc->start_before_dma = asrc_priv->soc->start_before_dma;
 	asrc->get_dma_channel = fsl_asrc_get_dma_channel;
 	asrc->request_pair = fsl_asrc_request_pair;
 	asrc->release_pair = fsl_asrc_release_pair;
@@ -1289,6 +1310,7 @@ static int fsl_asrc_probe(struct platform_device *pdev)
 	asrc->m2m_get_maxburst = fsl_asrc_m2m_get_maxburst;
 	asrc->m2m_pair_resume = fsl_asrc_m2m_pair_resume;
 	asrc->m2m_get_cap = fsl_asrc_m2m_get_cap;
+	asrc->m2m_output_ready = fsl_asrc_m2m_output_ready;
 
 	if (of_device_is_compatible(np, "fsl,imx35-asrc")) {
 		asrc_priv->clk_map[IN] = input_clk_map_imx35;

sound/soc/fsl/fsl_asrc.h

@@ -257,6 +257,8 @@
 #define ASRFSTi_OUTPUT_FIFO_WIDTH	7
 #define ASRFSTi_OUTPUT_FIFO_SHIFT	12
 #define ASRFSTi_OUTPUT_FIFO_MASK	(((1 << ASRFSTi_OUTPUT_FIFO_WIDTH) - 1) << ASRFSTi_OUTPUT_FIFO_SHIFT)
+#define ASRFSTi_OUTPUT_FIFO_FILL(v)	\
+	(((v) & ASRFSTi_OUTPUT_FIFO_MASK) >> ASRFSTi_OUTPUT_FIFO_SHIFT)
 #define ASRFSTi_IAEi_SHIFT		11
 #define ASRFSTi_IAEi_MASK		(1 << ASRFSTi_IAEi_SHIFT)
 #define ASRFSTi_IAEi			(1 << ASRFSTi_IAEi_SHIFT)
@@ -432,10 +434,12 @@ struct dma_block {
  *
  * @use_edma: using edma as dma device or not
  * @channel_bits: width of ASRCNCR register for each pair
+ * @start_before_dma: start asrc before dma
  */
 struct fsl_asrc_soc_data {
 	bool use_edma;
 	unsigned int channel_bits;
+	bool start_before_dma;
 };
 
 /**

sound/soc/fsl/fsl_asrc_common.h

@@ -107,6 +107,7 @@ struct fsl_asrc_pair {
  * @asrc_rate: default sample rate for ASoC Back-Ends
  * @asrc_format: default sample format for ASoC Back-Ends
  * @use_edma: edma is used
+ * @start_before_dma: start asrc before dma
  * @get_dma_channel: function pointer
  * @request_pair: function pointer
  * @release_pair: function pointer
@@ -116,6 +117,7 @@ struct fsl_asrc_pair {
  * @m2m_start: function pointer
  * @m2m_unprepare: function pointer
  * @m2m_stop: function pointer
+ * @m2m_output_ready: function pointer, check output fifo ready or not
  * @m2m_calc_out_len: function pointer
  * @m2m_get_maxburst: function pointer
  * @m2m_pair_suspend: function pointer
@@ -143,6 +145,7 @@ struct fsl_asrc {
 	int asrc_rate;
 	snd_pcm_format_t asrc_format;
 	bool use_edma;
+	bool start_before_dma;
 
 	struct dma_chan *(*get_dma_channel)(struct fsl_asrc_pair *pair, bool dir);
 	int (*request_pair)(int channels, struct fsl_asrc_pair *pair);
@@ -154,6 +157,7 @@ struct fsl_asrc {
 	int (*m2m_start)(struct fsl_asrc_pair *pair);
 	int (*m2m_unprepare)(struct fsl_asrc_pair *pair);
 	int (*m2m_stop)(struct fsl_asrc_pair *pair);
+	bool (*m2m_output_ready)(struct fsl_asrc_pair *pair);
 
 	int (*m2m_calc_out_len)(struct fsl_asrc_pair *pair, int input_buffer_length);
 	int (*m2m_get_maxburst)(u8 dir, struct fsl_asrc_pair *pair);

sound/soc/fsl/fsl_asrc_m2m.c

@@ -253,15 +253,21 @@ static int asrc_m2m_device_run(struct fsl_asrc_pair *pair, struct snd_compr_task
 	reinit_completion(&pair->complete[IN]);
 	reinit_completion(&pair->complete[OUT]);
 
+	if (asrc->start_before_dma)
+		asrc->m2m_start(pair);
+
 	/* Submit DMA request */
 	dmaengine_submit(pair->desc[IN]);
 	dma_async_issue_pending(pair->desc[IN]->chan);
 	if (out_dma_len > 0) {
+		if (asrc->start_before_dma && asrc->m2m_output_ready)
+			asrc->m2m_output_ready(pair);
 		dmaengine_submit(pair->desc[OUT]);
 		dma_async_issue_pending(pair->desc[OUT]->chan);
 	}
 
-	asrc->m2m_start(pair);
+	if (!asrc->start_before_dma)
+		asrc->m2m_start(pair);
 
 	if (!wait_for_completion_interruptible_timeout(&pair->complete[IN], 10 * HZ)) {
 		dev_err(dev, "out DMA task timeout\n");