[RFC PATCH 1/3] ASoC: soc-pcm: tweak DPCM BE hw_param() call order

[Sameer Pujar]

For DPCM links, the order of hw_param() call depends on the sequence of
BE connection to FE. It is possible that one BE link can provide clock
to another BE link. In such cases consumer BE DAI, to get the rate set
by provider BE DAI, can use the standard clock functions only if provider
has already set the appropriate rate during its hw_param() stage.

Presently the order is fixed and does not depend on the provider and
consumer relationships. So the clock rates need to be known ahead of
hw_param() stage.

This patch tweaks the hw_param() order by connecting the provider BEs
late to a FE. With this hw_param() calls for provider BEs happen first
and then followed by consumer BEs. The consumers can use the standard
clk_get_rate() function to get the rate of the clock they depend on.

Signed-off-by: Sameer Pujar <spujar at nvidia.com>
---
 TODO:
  * The FE link is not considered in this. For Tegra it is fine to
    call hw_params() for FE at the end. But systems, which want to apply
    this tweak for FE as well, have to extend this tweak to FE.
  * Also only DPCM is considered here. If normal links require such
    tweak, it needs to be extended.

 sound/soc/soc-pcm.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 59 insertions(+), 1 deletion(-)

diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
index 941410c..cfaff25 100644
--- a/sound/soc/soc-pcm.c
+++ b/sound/soc/soc-pcm.c
@@ -1442,6 +1442,29 @@ static int dpcm_prune_paths(struct snd_soc_pcm_runtime *fe, int stream,
 	return prune;
 }
 
+static bool defer_dpcm_be_connect(struct snd_soc_pcm_runtime *rtd)
+{
+	struct snd_soc_dai *dai;
+	int i;
+
+	if (!(rtd->dai_link->dai_fmt & SND_SOC_DAIFMT_FORMAT_MASK))
+		return false;
+
+	if ((rtd->dai_link->dai_fmt & SND_SOC_DAIFMT_CLOCK_PROVIDER_MASK) ==
+	    SND_SOC_DAIFMT_CBC_CFC) {
+
+		for_each_rtd_cpu_dais(rtd, i, dai) {
+
+			if (!snd_soc_dai_is_dummy(dai))
+				return true;
+		}
+	}
+
+	return false;
+}
+
+#define MAX_CLK_PROVIDER_BE 10
+
 static int dpcm_add_paths(struct snd_soc_pcm_runtime *fe, int stream,
 	struct snd_soc_dapm_widget_list **list_)
 {
@@ -1449,7 +1472,8 @@ static int dpcm_add_paths(struct snd_soc_pcm_runtime *fe, int stream,
 	struct snd_soc_dapm_widget_list *list = *list_;
 	struct snd_soc_pcm_runtime *be;
 	struct snd_soc_dapm_widget *widget;
-	int i, new = 0, err;
+	struct snd_soc_pcm_runtime *prov[MAX_CLK_PROVIDER_BE];
+	int i, new = 0, err, count = 0;
 
 	/* Create any new FE <--> BE connections */
 	for_each_dapm_widgets(list, i, widget) {
@@ -1489,6 +1513,40 @@ static int dpcm_add_paths(struct snd_soc_pcm_runtime *fe, int stream,
 		    (be->dpcm[stream].state != SND_SOC_DPCM_STATE_CLOSE))
 			continue;
 
+		/* Connect clock provider BEs at the end */
+		if (defer_dpcm_be_connect(be)) {
+			if (count >= MAX_CLK_PROVIDER_BE) {
+				dev_err(fe->dev, "ASoC: too many clock provider BEs\n");
+				return -EINVAL;
+			}
+
+			prov[count++] = be;
+			continue;
+		}
+
+		/* newly connected FE and BE */
+		err = dpcm_be_connect(fe, be, stream);
+		if (err < 0) {
+			dev_err(fe->dev, "ASoC: can't connect %s\n",
+				widget->name);
+			break;
+		} else if (err == 0) /* already connected */
+			continue;
+
+		/* new */
+		dpcm_set_be_update_state(be, stream, SND_SOC_DPCM_UPDATE_BE);
+		new++;
+	}
+
+	/*
+	 * Now connect clock provider BEs. A late connection means,
+	 * these BE links appear first in the list maintained by FE
+	 * and hw_param() call for these happen first.
+	 */
+	for (i = 0; i < count; i++) {
+
+		be = prov[i];
+
 		/* newly connected FE and BE */
 		err = dpcm_be_connect(fe, be, stream);
 		if (err < 0) {
-- 
2.7.4