linux-kernel - Re: [PATCH v14 20/53] ASoC: Add SOC USB APIs for adding an USB backend

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Date: Fri, 9 Feb 2024 12:34:39 -0800
From: Wesley Cheng <quic_wcheng@...cinc.com>
To: Takashi Iwai <tiwai@...e.de>
CC: <srinivas.kandagatla@...aro.org>, <mathias.nyman@...el.com>,
        <perex@...ex.cz>, <conor+dt@...nel.org>, <corbet@....net>,
        <lgirdwood@...il.com>, <andersson@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <gregkh@...uxfoundation.org>,
        <Thinh.Nguyen@...opsys.com>, <broonie@...nel.org>,
        <bgoswami@...cinc.com>, <tiwai@...e.com>, <robh+dt@...nel.org>,
        <konrad.dybcio@...aro.org>, <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 v14 20/53] ASoC: Add SOC USB APIs for adding an USB
 backend

Hi Takashi,

On 2/9/2024 2:54 AM, Takashi Iwai wrote:
> On Fri, 09 Feb 2024 00:13:33 +0100,
> Wesley Cheng wrote:
>>
>> Some platforms may have support for offloading USB audio devices to a
>> dedicated audio DSP.  Introduce a set of APIs that allow for management of
>> USB sound card and PCM devices enumerated by the USB SND class driver.
>> This allows for the ASoC components to be aware of what USB devices are
>> available for offloading.
>>
>> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
> (snip)
>> --- a/sound/soc/Makefile
>> +++ b/sound/soc/Makefile
>> @@ -1,5 +1,5 @@
>>   # SPDX-License-Identifier: GPL-2.0
>> -snd-soc-core-objs := soc-core.o soc-dapm.o soc-jack.o soc-utils.o soc-dai.o soc-component.o
>> +snd-soc-core-objs := soc-core.o soc-dapm.o soc-jack.o soc-usb.o soc-utils.o soc-dai.o soc-component.o
>>   snd-soc-core-objs += soc-pcm.o soc-devres.o soc-ops.o soc-link.o soc-card.o
>>   snd-soc-core-$(CONFIG_SND_SOC_COMPRESS) += soc-compress.o
> 
> Do we really want to build this into ASoC core unconditionally?
> This is very specific to Qualcomm USB-offload stuff, so it's better to
> factor out.
> 

Ideally, the SOC USB part shouldn't be Qualcomm specific.  Since I don't 
have access or insight into how other vendors are achieving the same 
thing, I can only base the soc-usb layer to work with the information 
that is required to get the audio stream up and running on the QC 
platforms.  In its simplest form, its basically just a SW entity that 
notifies ASoC components about changes occurring from USB SND, and I 
think all vendors that have an ASoC based platform card handling the 
offload will need this notification.

Thanks
Wesley Cheng