[pulseaudio-discuss] [RFC] Dynamically created PCM devices for HDMI/DisplayPort

[Tanu Kaskinen]

Replying to a couple of months old thread...

On Tue, 2015-06-30 at 18:08 +0300, Tanu Kaskinen wrote:
> When module-udev-detect sees a new PCM device, it needs to notify 
> module-alsa-card about it. module-udev-detect's only interface with 
> module-alsa-card is pa_module, which is not useful for adding the 
> notification. I think we should move the bulk of the code in 
> module-alsa-card.c to a new class: pa_alsa_card. module-udev-detect 
> would then create pa_alsa_card objects instead of loading 
> module-alsa-card instances. module-alsa-card would still exist as a 
> wrapper around pa_alsa_card, but the module would not be used by 
> module-udev-detect. With pa_alsa_card in place, we can add a 
> pa_alsa_card_pcm_added() function to its API.
> 
> pa_alsa_card should be defined in src/modules/alsa/alsa-card.[ch] and 
> included in the libalsa-util.la helper library.

In IRC, Arun recently pointed out a problem in replacing module loading
with creation of pa_alsa_card objects: users rely on the module
interface to unload individual alsa cards, so users won't any more be
able to unload cards that have been loaded by module-udev-detect (the
main use case for that is probably debugging; you may want to reload
module-alsa-card with different parameters than what module-udev-detect
used).

I propose the following solution: module-udev-detect will still load
module-alsa-card instances using pa_module_load() like before, but
pa_alsa_card objects will be created too. When module-alsa-card is
loaded, it creates a pa_alsa_card instance and adds it to a registry
from which module-udev-detect can look it up using the module index as
the key. That way users still can unload cards, and module-udev-detect
still has access to the pa_alsa_card API.

-- 
Tanu