[PATCH] ASoC: Intel: avs: Initialize private data for subsequent HDA FEs

[Cezary Rojewski]

HDAudio implementation found in sound/pci/hda expects a valid stream
pointer in substream->runtime->private_data location. For ASoC users,
that should point to a valid link stream which is assigned when BE
opens.

As BE borrows its runtime from FE, the information may be lost when
reparenting comes into picture - see dpcm_be_reparent(). To support the
DPCM reparenting functionality for HDAudio scenarios while still
fulfilling expectations of HDAudio common code, have all FEs point to
the same private data.

Signed-off-by: Cezary Rojewski <cezary.rojewski at intel.com>
---

This is a tough one and spawned a range of patches. Some of the
discussion is present at thesofproject/linux [1]. In the end decided to
drop any soc-core/pcm.c modifications for now, instead addressing the
problem directly in the avs-driver. Long term - perhaps BE should have a
separate runtime so there is no ambiguity between FE and BE.

[1]: https://github.com/thesofproject/linux/pull/3987

 sound/soc/intel/avs/pcm.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/sound/soc/intel/avs/pcm.c b/sound/soc/intel/avs/pcm.c
index e237ab23fef9..41030aaae02d 100644
--- a/sound/soc/intel/avs/pcm.c
+++ b/sound/soc/intel/avs/pcm.c
@@ -1507,9 +1507,29 @@ static int avs_component_hda_open(struct snd_soc_component *component,
 
 	if (!rtd->dai_link->no_pcm) {
 		struct snd_pcm_hardware hwparams = avs_pcm_hardware;
+		struct snd_soc_pcm_runtime *be;
+		struct snd_soc_dpcm *dpcm;
+		int dir = substream->stream;
+
+		/*
+		 * Support the DPCM reparenting while still fulfilling expectations of HDAudio
+		 * common code - a valid stream pointer at substream->runtime->private_data -
+		 * by having all FEs point to the same private data.
+		 */
+		for_each_dpcm_be(rtd, dir, dpcm) {
+			struct snd_pcm_substream *be_substream;
+
+			be = dpcm->be;
+			if (be->dpcm[dir].users == 1)
+				break;
+
+			be_substream = snd_soc_dpcm_get_substream(be, dir);
+			substream->runtime->private_data = be_substream->runtime->private_data;
+			break;
+		}
 
 		/* RESUME unsupported for de-coupled HD-Audio capture. */
-		if (substream->stream == SNDRV_PCM_STREAM_CAPTURE)
+		if (dir == SNDRV_PCM_STREAM_CAPTURE)
 			hwparams.info &= ~SNDRV_PCM_INFO_RESUME;
 
 		return snd_soc_set_runtime_hwparams(substream, &hwparams);
-- 
2.25.1