[alsa-devel] [PATCH v2 05/10] ASoC: Add support for dummy DAI links and PCM runtimes

[Mark Brown]

On Mon, Aug 10, 2015 at 10:47:47PM +0800, mengdong.lin at intel.com wrote:

> Add dummy flag to a DAI link and PCM runtime. A dummy link will create
> a dummy PCM runtime.

> A machine driver can define dummy dai links to specify the expected
> platform and codec. And its dummy runtime is used to probe the platform
> and codec components, which can bring real DAI/DAI links based on topology.
> After components probing, all dummy PCM runtimes will be removed.

This isn't very clear to me either in terms of the description or the
interface.  As far as I can tell these links that are being created here
are placeholders representing links that will actually be instantiated
later but if that's the case they're not really dummies as I'd
understand them, they are real links which physically exist and will be
created later by topology data.  If we are going to do things this way
we need a better way of talking about these not yet instantiated links.

I'm really confused as to why physical links that exist in the board are
coming in via topology information loaded from userspace - it's not like
the DSP firmware is going to be able to physically connect the DSP to
things where no links existed before.  I'd expect that these links are
connections between physical devices which just exist in the system and
that while the topology information might leave some of them dangling
they wouldn't be created or removed.

Presumably we're also going to need to handle the case where the
firmware is unloaded and we destroy the links if we do this...
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