Re: [PATCH v21 22/39] ALSA: usb-audio: Prevent starting of audio stream if in use

From: Wesley Cheng
Date: Wed May 08 2024 - 19:40:51 EST


Hi Pierre,

On 5/7/2024 2:20 PM, Pierre-Louis Bossart wrote:

If a PCM device is already in use, the check will return an error to
userspace notifying that the stream is currently busy. This ensures that
only one path is using the USB substream.

What was the point of having a "USB Mixer" then?

The USB mixer is intended to enable/route the USB offloading path to the audio DSP, and is for controlling the ASoC specific entities. This change is needed to resolve any contention between the USB SND PCM device (non offload path) and the ASoC USB BE DAI (offload path).

Thanks
Wesley Cheng