Re: [PATCH v21 34/39] ALSA: usb-audio: Add USB offloading capable kcontrol

[Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>]

>>>> It is expected for the USB offloading driver to add the kcontrol to the
>>>> sound card associated with the USB audio device.  An example output
>>>> would
>>>> look like:
>>>>
>>>> tinymix -D 1 get 'USB Offload Playback Capable Card'
>>>> 0 (range -1->32)
>>>
>>> You already gave the following examples in patch 29:
>>>
>>> "
>>> USB offloading idle:
>>> tinymix -D 0 get 'USB Offload Playback Route Status'
>>> -->-1, -1 (range -1->32)
>>>
>>> USB offloading active(USB card#1 pcm#0):
>>> tinymix -D 0 get 'USB Offload Playback Route Status'
>>> -->1, 0 (range -1->32)
>>> "
>>>
>>> Can you clarify how many controls there would be in the end?
>>
>> For USB offload situations, there will be a set of controls for
>> playback status and playback select.  The offload jack will also be
>> there to tell us if there is an offload path available for the
>> platform ASoC sound card.
>>
>>> Also isn't tinymix -D N going to give you the controls for card N?
>>>
>>
>> Yes, since the offload portion is handled as a DPCM DAI link to the
>> platform ASoC card, it will be included as a kcontrol for that.
>>
>> Thanks
>> Wesley Cheng
>>
>>
> 
> Sorry for responding again.  I read your email again, and wanted to also
> add that aside from the above, which are all within the ASoC layer, as
> we discussed previously, we should have a kcontrol in the USB SND card
> to determine if there is an ASoC platform card capable of offloading.
> This is also available from the SND card created by the USB audio device.

That makes sense: if the application wanted to use a given endpoint, it
could check if there is a 'better' path exposed by another card. It'd be
a lot easier than reading controls from random cards.

Was this part of this patchset or more of an idea for a future addition?