[alsa-devel] Confusion about Playback/Capture, CODEC/CODEC links, and snd_soc_dapm_link_dai_widgets()

Stephen Warren swarren at wwwdotorg.org
Tue Jun 5 23:17:15 CEST 2012

On 06/05/2012 02:48 PM, Mark Brown wrote:
> On Tue, Jun 05, 2012 at 02:24:47PM -0600, Stephen Warren wrote:
>> Initially, I thought that snd_soc_dapm_new_dai_widgets() could just
>> return if the DAI already had widgets, but that doesn't work, since the
>> widgets were created for the wrong DAPM context - the I2S1 DAP DAI's
>> rather than the I2S CODEC's.
>> Perhaps instead of blindly probing the CPU DAI, soc_probe_dai_link()
>> should check whether that DAI is part of a CODEC, and instead of calling
>> try_module_get() and snd_soc_dapm_new_dai_widgets(), it should just call
>> soc_probe_codec() on the parent CODEC (guarded by whether the CODEC was
>> already probed). Does that sound right? I'm attempting to make that work
>> now, in case it's right.
> No, we should just probe CODECs sensibly before we do any of the DAIs
> instead of trying to guess what we're doing in the middle of handling
> the DAI links.  Your changes will be making the logic even more
> complicated here, it should be getting simpler - the reason this blew up
> for you is that the probe logic is already far too baroque.  Given the
> data we have it'll boil down to similar checks bit it'll be in a clear,
> comprehensible CODEC probe step rather than intertwined with other
> stuff.  This will also mean that aux_devs make more sense.

OK, that's actually what my inclination was, but I wasn't sure about
changing all the probing in such a radical way, so I didn't mention it.

So, should the logic be something like this early-ish in

for every dai link:
    if cpu side is a codec and it isn't probed
        probe it
    if codec side isn't probed
        probe it
something similar for aux devs
something similar for platforms?

And modify soc_probe_dai_link() to only probe DAIs, never anything else.

Is the following loop still required:

> 	/* early DAI link probe */
> 			order++) {

I'm not sure what the probe ordering stuff is achieving, and whether
it's really intended for just CPU DAIs, just all DAIs, just CODECS,

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