[alsa-devel] [RFC 0/4] Add support for DAI link addition dynamically

[Mengdong Lin]

On 02/17/2016 01:52 PM, Mengdong Lin wrote:
>
>
> On 02/15/2016 10:22 PM, Lars-Peter Clausen wrote:
>> On 02/15/2016 01:19 PM, Vaibhav Agarwal wrote:
>>> Following patches are based on for-next branch from broonie tree.
>>> First 2 patches include changes in existing soc, core framework
>>> to prepare for adding support for dynamic DAI link addition/
>>> removal
>>>
>>> Patch 3 & 4 contains actual changes to enable dynamic DAI link
>>> support
>>>
>>> NOTE:
>>> Currently, the code is tested on Pandaboad ES revB3 for playback
>>> usecase.
>>
>> Can you outline how exactly that would work?
>>
>> Thanks,
>> - Lars
>>
>>
>
> In Agarwal's use case, it seems a removable codec driver can be
> registered after the sound card is registered. And the Pandaboard
> machine driver need to add new BE links brought by the new codec
> component, which will further trigger probing of the codec components.
>
> How can the machine driver know a new codec component is registered
> automatically?
>
> Can we add a notification ops like "new_component" to a soc card?
> A machine driver can implement this ops.  So when a new component is
> registered to the ASoC core, all instantiated soc cards can get notified
> and the machine driver can check if the new component brings some new
> links to the soc card in this ops. e.g. the Pandaboard machine driver
> can add new BE links for the new codec.
>
> Thanks
> Mengdong
>

Sorry, I missed the case that the codec component can be still be 
registered before the machine driver register the card. In this 
situation, the machine driver cannot get the notification.

I wonder if the machine driver can still predefine these links but flag 
them as "dynamically_registered". For such links, asoc core will not 
abort instantiating the card, i.e. the sound card will be created even 
if these links are not bound because lack of some DAIs (e.g. the DAIs of 
the codec component not registered yet).

Then when the missing component is added, the ASOC core will 
automatically check these the unbound links and bind them. When the 
component is unregistered, ASoC will try to remove the affected links 
and then remove the components.

Thus we may not need add new APIs or let the machine driver monitor when 
the codec component is registered.

Thanks
Mengdong