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

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Date: Sun, 11 Feb 2024 23:58:31 -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 2/10/2024 12:08 AM, Takashi Iwai wrote:
> On Fri, 09 Feb 2024 21:34:39 +0100,
> Wesley Cheng wrote:
>>
>> 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.
> 
> Yes, but it's not necessarily built into the snd-soc-core module at
> all, but can be split to another module, right?  Otherwise all
> machines must load this code even if it doesn't use at all.
> If this were common among various chips, it'd be worth to be merged
> into the default common module.  But I don't think that's the case.
> 

That's fair.  I'll make it a separate module and upload v15 tomorrow. 
Thanks for the explanation.

Thanks
Wesley Cheng