Hi Pierre,
On 5/9/2024 6:01 AM, Pierre-Louis Bossart wrote:
On 5/8/24 18:40, Wesley Cheng wrote:
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).
Not following, sorry. Is the "USB Mixer" some sort of hardware entity
related to USB offload or just a pure DAPM processing widget handling
volume and actual mixing between streams?
It controls which Multimedia (ASM) stream can be routed to the USB BE DAI.
I was trying to get clarity on whether there can be multiple streams
mixed before going to the USB endpoint. The commit message "only one
path is using the USB substream" is ambiguous, not sure if you are
referring to mutual exclusion between offloaded and non-offloaded paths,
or number of streams when offloaded is supported. Different concepts/levels.
Ideally we shouldn't. Only one ASM stream should be allowed to open the
USB AFE port at a time.
Thanks
Wesley Cheng
