linux-kernel - Re: [PATCH v21 34/39] ALSA: usb-audio: Add USB offloading capable kcontrol

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Date: Wed, 8 May 2024 12:41:10 -0700
From: Wesley Cheng <quic_wcheng@...cinc.com>
To: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.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 34/39] ALSA: usb-audio: Add USB offloading capable
 kcontrol

Hi Pierre,

On 5/7/2024 2:37 PM, Pierre-Louis Bossart wrote:
> 
> 
> On 5/7/24 14:51, Wesley Cheng wrote:
>> In order to allow userspace/applications know about USB offloading status,
>> expose a sound kcontrol that fetches information about which sound card
>> index is associated with the ASoC platform card supporting offloading.  In
>> the USB audio offloading framework, the ASoC BE DAI link is the entity
>> responsible for registering to the SOC USB layer.  SOC USB will expose more
>> details about the current offloading status, which includes the USB sound
>> card and USB PCM device indexes currently being used.
>>
>> It is expected for the USB offloading driver to add the kcontrol to the
>> sound card associated with the USB audio device.  An example output would
>> look like:
>>
>> tinymix -D 1 get 'USB Offload Playback Capable Card'
>> 0 (range -1->32)
> 
> You already gave the following examples in patch 29:
> 
> "
> USB offloading idle:
> tinymix -D 0 get 'USB Offload Playback Route Status'
> -->-1, -1 (range -1->32)
> 
> USB offloading active(USB card#1 pcm#0):
> tinymix -D 0 get 'USB Offload Playback Route Status'
> -->1, 0 (range -1->32)
> "
> 
> Can you clarify how many controls there would be in the end?

For USB offload situations, there will be a set of controls for playback 
status and playback select.  The offload jack will also be there to tell 
us if there is an offload path available for the platform ASoC sound card.

> Also isn't tinymix -D N going to give you the controls for card N?
> 

Yes, since the offload portion is handled as a DPCM DAI link to the 
platform ASoC card, it will be included as a kcontrol for that.

Thanks
Wesley Cheng