ASoC dailink capture/playback flags

[Pierre-Louis Bossart]

Hi,

Some of us at Intel are confused with multiple definitions of 
capture/playback dailink flags (credits to Rander Wang for reporting 
this in https://github.com/thesofproject/linux/pull/2070).

struct snd_soc_dai_link {
[...]

     /* For unidirectional dai links */
     unsigned int playback_only:1;
     unsigned int capture_only:1;

[...]

     /* DPCM capture and Playback support */
     unsigned int dpcm_capture:1;
     unsigned int dpcm_playback:1;
[...]

};

And of course when you start looking at some machine drivers, there are 
confusions, e.g. below with DPCM front-ends using one or the other set, 
and with copy-paste and partial diffs, this propagates without being 
consistent or being noticed:

     [GLK_DPCM_AUDIO_HS_PB] = {
         .name = "Glk Audio Headset Playback",
         .stream_name = "Headset Audio",
         .dpcm_playback = 1, <<<<
         .nonatomic = 1,
         .dynamic = 1,
         SND_SOC_DAILINK_REG(system2, dummy, platform),
     },
     [GLK_DPCM_AUDIO_ECHO_REF_CP] = {
         .name = "Glk Audio Echo Reference cap",
         .stream_name = "Echoreference Capture",
         .init = NULL,
         .capture_only = 1, <<<< should this be .dpcm_capture = 1?
         .nonatomic = 1,
         .dynamic = 1,
         SND_SOC_DAILINK_REG(echoref, dummy, platform),
     },
     [GLK_DPCM_AUDIO_REF_CP] = {
         .name = "Glk Audio Reference cap",
         .stream_name = "Refcap",
         .init = NULL,
         .dpcm_capture = 1, <<<<
         .nonatomic = 1,
         .dynamic = 1,
         .ops = &geminilake_refcap_ops,
         SND_SOC_DAILINK_REG(reference, dummy, platform),
     },

So here are the questions:

- when using DPCM, is there an expectation to use dpcm_ flags only?

- should we instead use playback/capture_only when only one of the two 
dpcm_ flags is set?

- should we flags errors if we ever encounter cases with e.g. 
dpcm_playback = true and capture_only = true?

- do we actually need two sets of definitions? There are very few users 
of the .playback_only and .capture_only flags and only a single place 
where it's checked in soc-pcm.c

Thanks for your feedback

-Pierre