[alsa-devel] Question about struct snd_soc_dai() :: cpu_dai->codec

[Mark Brown]

On Sat, Jul 30, 2016 at 06:45:04AM +0900, Takashi Sakamoto wrote:

> In a point of 'reuse of codes', I cannot imagine what Lars said for USB
> devices, then post the questions.

Someone might make a fancy device connected via USB which doesn't
conform to the USB specs.

> But I think it's logically difficult to manage state of sound card; e.g.
> disconnect. When one sound card instance consists of instances of
> several 'DAI', 'Codecs' and 'Components' (this 'component' is not in
> ALSA core contexts[1]) and we try to unload one of them, then which
> state the card should be assigned to? Or no 'Codecs' drivers are loaded,
> then which state should be assigned to the card?

The card only instantiates when all the components of the card are
present, until then it defers probe.

> Additionally, when old Codec driver is unloaded and new Codec driver is
> loaded, then what should we do for corresponding PCM character devices
> are? Currently, once snd_card_regsiter() is called, we cannot
> insert/delete ALSA components such like PCM.

The card should be deinstantiated and reinstantiated whenever a
component driver unbinds and rebinds (respectively).  You'd need to
completely deregister the card to change the list of things it's
expecting currently.
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