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

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Message-ID: <a0d19e7c-8fb0-e93a-d79b-319d8339504a@quicinc.com>
Date: Wed, 8 May 2024 17:42:09 -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 5/8/2024 12:41 PM, Wesley Cheng wrote:
> 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
> 
> 

Sorry for responding again.  I read your email again, and wanted to also 
add that aside from the above, which are all within the ASoC layer, as 
we discussed previously, we should have a kcontrol in the USB SND card 
to determine if there is an ASoC platform card capable of offloading. 
This is also available from the SND card created by the USB audio device.

Thanks
Wesley Cheng