Hi,
ALSA ASoC DPCM FE - BE connection doesn't handle the scenario when a machine
driver has multiple FEs linking to same codec type.
Let me use dummy codec as example codec:
FE1 - BE1 (connected to dummy codec instance #1)
FE2 - BE2 (connected to dummy codec instance #2)
FE3 - BE3 (connected to dummy codec instance #3)
DPCM will not be able to correctly identify the Back End from the 2nd pair
onwards.
This happens as the codec .stream_name is used 3 times to connect to different
Back-Ends.
Say I am using the dummy codec that has a playback .stream_name "Dummy
Playback" with 3 I2S AIF.
E.g. I have 3 BE dai links:
static struct snd_soc_dai_link xxx_dailink[] = {
...
{
.name = "I2S0-Codec",
.be_id = 1,
.cpu_dai_name = "i2s0-port",
.platform_name = "xxx-platform",
.no_pcm = 1,
.codec_dai_name = "snd-soc-dummy-dai",
.codec_name = "snd-soc-dummy",
}
{
.name = "I2S1-Codec",
.be_id = 2,
.cpu_dai_name = "i2s1-port",
.platform_name = "xxx-platform",
.no_pcm = 1,
.codec_dai_name = "snd-soc-dummy-dai",
.codec_name = "snd-soc-dummy",
}
{
.name = "I2S2-Codec",
.be_id = 3,
.cpu_dai_name = "i2s2-port",
.platform_name = "xxx-platform",
.no_pcm = 1,
.codec_dai_name = "snd-soc-dummy-dai",
.codec_name = "snd-soc-dummy",
}
/*DAPM routing*/
static const struct snd_soc_dapm_route map[] = {
{ "Dummy Playback", NULL, "I2S0 Tx"},
{ "Dummy Playback", NULL, "I2S1 Tx"},
{ "Dummy Playback", NULL, "I2S2 Tx"},
...
}
The order of the DAI Link affects the connection of the codec stream name
widget on a first come first serve basis, in this case, first declared DAI
link codec is used.
In soc-pcm.c, when dpcm_fe_dai_open tries to add paths for the 2nd(and later)
FE, dpcm_add_paths function will always discover the "Dummy Playback" widget
belonging to the back-end of the first DAI link and link it incorrectly.
1. dpcm_add_paths() finds "Dummy Playback" is a snd_soc_dapm_dai_in type, and
calls dpcm_get_be()
1101 static int dpcm_add_paths(struct snd_soc_pcm_runtime *fe, int
stream,
1102 struct snd_soc_dapm_widget_list **list_)
...
1120 /* is there a valid BE rtd for this widget */
1121 be = dpcm_get_be(card, list->widgets[i],
stream);
2. The dpcm_get_be will traverse the list for "Dummy Playback" and return the
first back end found.
Line 994 below always finds that I2S0-Codec link matches this condition and
will not proceed further to match I2S1-Codec
990 if (stream == SNDRV_PCM_STREAM_PLAYBACK) {
991 for (i = 0; i < card->num_links; i++) {
992 be = &card->rtd[i];
993
994 if (!be->dai_link->no_pcm)
995 continue;
996
997 if (be->cpu_dai->playback_widget == widget ||
998 be->codec_dai->playback_widget == widget)
999 return be;
1000 }
1001 } else { --> Same effect also happens in the capture path.
E.g. When I try to playback on the i2s1 (2nd playback device), the following
fe-be link happens :
Widget = "I2S1 Tx", Back End = "I2S1-Codec" --> This is the
intended link.
Widget = "Dummy Playback", Back End = "I2S0-Codec" --> This is additional
problematic link because the first discovered "Dummy Playback" is from the
codec in the first DAI link.
This results in soc_pcm_open called twice in dpcm_be_dai_startup function;
first for the first Back End (undesired), and then only the correct Back End
Is it possible to add some instance id to the codec name, or some check on the
intended FE-BE pairing?
Regards,
Joshua
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