linux-kernel - Re: [PATCH v24 23/34] ALSA: usb-audio: Prevent starting of audio stream if in use

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Message-ID: <186ae30f-678c-423a-a56f-74510a184f99@linux.intel.com>
Date: Tue, 6 Aug 2024 16:51:57 +0200
From: Amadeusz Sławiński
 <amadeuszx.slawinski@...ux.intel.com>
To: Wesley Cheng <quic_wcheng@...cinc.com>, srinivas.kandagatla@...aro.org,
 mathias.nyman@...el.com, perex@...ex.cz, conor+dt@...nel.org,
 corbet@....net, broonie@...nel.org, lgirdwood@...il.com, krzk+dt@...nel.org,
 Thinh.Nguyen@...opsys.com, bgoswami@...cinc.com, tiwai@...e.com,
 gregkh@...uxfoundation.org, robh@...nel.org
Cc: linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 linux-sound@...r.kernel.org, linux-usb@...r.kernel.org,
 linux-arm-msm@...r.kernel.org, linux-doc@...r.kernel.org,
 alsa-devel@...a-project.org
Subject: Re: [PATCH v24 23/34] ALSA: usb-audio: Prevent starting of audio
 stream if in use

On 8/1/2024 3:17 AM, Wesley Cheng wrote:
> With USB audio offloading, an audio session is started from the ASoC
> platform sound card and PCM devices.  Likewise, the USB SND path is still
> readily available for use, in case the non-offload path is desired.  In
> order to prevent the two entities from attempting to use the USB bus,
> introduce a flag that determines when either paths are in use.
> 

How can this happen? Can you provide some example with list of devices 
and which one should block the other? If I recall correctly devices are 
already exclusive unless you support substreams which ASoC does not at 
the moment.