[alsa-devel] DPCM: BE to BE cpu DAIs question

[Chuang Eric]

Hi,        Our platform use ASoC structure. Currently, we want to refactor our driver to use DPCM structure.I followed the documentation of DPCM, but have some trouble  implementing hostless  BE to BE dai links.
My question is:1.  Is there any  code example for this(hostless BE to BE)?Since I didn't see any existing code on  linux kernel.2.  From  documentation,  i have to assgin  a  snd_soc_pcm_stream for BE dais.     It seems that the BE<->BE dai links can only support one spec (format/rates/ch).    Or am i getting it wrong, does it support dynamically change of the spec?
Thanks in advanced!
--------------------------------------------------------------------------------------  I have  tried some  implementations, but failed.  My linux version is 3.18.
Illustration,PCM -----------------> BE1                                       ↑                                          -------< BE2
Code snippet,
static const struct snd_soc_dapm_route machine_routes[] = {	{BE1_PLAYBACK_CPU_DAI_STNAME, NULL, FE_STNAME},	{BE1_PLAYBACK_CPU_DAI_STNAME, NULL, BE2_CAPTURE_CPU_DAI_STNAME},};
static const struct snd_soc_pcm_stream dai_params = {	.formats = SNDRV_PCM_FMTBIT_S32_LE,	.rate_min = 48000,	.rate_max = 48000,	.channels_min = 2,	.channels_max = 2,};
static struct snd_soc_dai_link mt_soc_dai_common[] = {		{			.name = FE_PCM,			.stream_name = FE_STNAME,			.cpu_dai_name = FE_CPUDAINAME,	// cannot use dummy!!!!			.platform_name = FE_PCMNAME,			.codec_name = "snd-soc-dummy",			.codec_dai_name = "snd-soc-dummy-dai",			.init = mt_soc_audio_init3,			.ops = &kc_snd_soc_ops,			.dynamic = 1,			.dpcm_playback = 1,			.trigger = {SND_SOC_DPCM_TRIGGER_POST, SND_SOC_DPCM_TRIGGER_POST},		 },		 /* BE DAIs */		{			.name = "BE2",			.cpu_dai_name = BE2_PLAYBACK_CPU_DAI, //"snd-soc-dummy-dai",			.platform_name = "snd-soc-dummy",			.codec_name = "snd-soc-dummy",			.codec_dai_name = "snd-soc-dummy-dai",			.dai_fmt = SND_SOC_DAIFMT_I2S | SND_SOC_DAIFMT_NB_NF |				SND_SOC_DAIFMT_CBS_CFS,			.no_pcm = 1,			.dpcm_playback = 1,			.dpcm_capture = 1,			.ignore_suspend = 1,			.ignore_pmdown_time = 1,			.params = &dai_params,		},		{			.name = BE1_PLAYBACK,			.cpu_dai_name = BE1_PLAYBACK_CPU_DAI,			.platform_name = "snd-soc-dummy",			.codec_name = "snd-soc-dummy",			.codec_dai_name = "snd-soc-dummy-dai",			.no_pcm = 1,			.dpcm_playback = 1,			.dpcm_capture = 1,			.ignore_suspend = 1,			.ignore_pmdown_time = 1,			.params = &dai_params,		},
1. when only  routes  PCM-->BE1,          If i add .params in BE1 soc dai link,  when i start PCM, it will crash. and get "Unable to handle kernel NULL pointer dereference at virtual address 000000d0"        Seems to crash in dpcm_be_dai_startup()         If i removed .params, it will not crash, and play normally.
2.  when only with BE2--> BE1,        BE2 is never trigger,  where did i  get wrong?
Thanks.