Add a kcontrol to the platform sound card to fetch the current offload status. This can allow for userspace to ensure/check which USB SND resources are actually busy versus having to attempt opening the USB SND devices, which will result in an error if offloading is active.
I think I mentioned this a while back, but why not add the status in the USB card itself? That's a generic component that all userspace agent could query. Having a QCOM-specific control doesn't make the life of userspace easier IMHO.
Will take a look at this based on the comments you had in the other kcontrol patch. Seeing if we can move it to a more generic layer.
I think it would make more sense to see if we can keep all the offload kcontrols under the sound card exposed by the platform. Especially, if we are going to modify the components string of the card to signify that it supports USB offload.
A two-way relationship would be ideal, i.e. - the USB card has an indicator that it's currently bound with another "platform" card that offers optimized offloaded capabilities. - the platform card has a indicator that it exposes one or more PCM devices routed to the USB card endpoint.
Android/HAL would typically start with the latter while other more generic solutions would start from the former.