linux-kernel - Re: [PATCH v21 27/39] ASoC: Introduce SND kcontrols to select sound card and PCM device

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Message-ID: <54b79b7b-49e6-418e-9a6b-11bcbada8398@linux.intel.com>
Date: Tue, 7 May 2024 16:26:09 -0500
From: Pierre-Louis Bossart <pierre-louis.bossart@...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, lgirdwood@...il.com, andersson@...nel.org,
 krzk+dt@...nel.org, gregkh@...uxfoundation.org, Thinh.Nguyen@...opsys.com,
 broonie@...nel.org, bgoswami@...cinc.com, tiwai@...e.com,
 bagasdotme@...il.com, robh@...nel.org, konrad.dybcio@...aro.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 v21 27/39] ASoC: Introduce SND kcontrols to select sound
 card and PCM device



On 5/7/24 14:51, Wesley Cheng wrote:
> Add SND kcontrol to SOC USB, which will allow for userpsace to determine
> which USB card number and PCM device to offload.  This allows for userspace
> to potentially tag an alternate path for a specific USB SND card and PCM
> device.  Previously, control was absent, and the offload path would be
> enabled on the last USB SND device which was connected.  This logic will
> continue to be applicable if no mixer input is received for specific device
> selection.
> 
> An example to configure the offload device using tinymix:
> tinymix -D 0 set 'USB Offload Playback Route Select' 1 0
> 
> The above command will configure the offload path to utilize card#1 and PCM
> stream#0.

I don't know how this is usable in practice. Using card indices is
really hard to do, it depends on the order in which devices are
plugged-in...