linux-kernel - Re: [PATCH v9 23/34] ALSA: usb-audio: Prevent starting of audio stream if in use

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Message-ID: <4ad7b474-257c-9934-8f1b-8ceb3a90af60@quicinc.com>
Date:   Wed, 18 Oct 2023 13:33:56 -0700
From:   Wesley Cheng <quic_wcheng@...cinc.com>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        <mathias.nyman@...el.com>, <gregkh@...uxfoundation.org>,
        <lgirdwood@...il.com>, <broonie@...nel.org>, <perex@...ex.cz>,
        <tiwai@...e.com>, <agross@...nel.org>, <andersson@...nel.org>,
        <konrad.dybcio@...aro.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
        <srinivas.kandagatla@...aro.org>, <bgoswami@...cinc.com>,
        <Thinh.Nguyen@...opsys.com>
CC:     <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <alsa-devel@...a-project.org>, <linux-arm-msm@...r.kernel.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v9 23/34] ALSA: usb-audio: Prevent starting of audio
 stream if in use

Hi Pierre,

On 10/17/2023 3:37 PM, Pierre-Louis Bossart wrote:
> 
> 
> On 10/17/23 15:00, Wesley Cheng wrote:
>> With USB audio offloading, an audio session is started from the ASoC
>> platform sound card and PCM devices.  Likewise, the USB SND path is still
>> readily available for use, in case the non-offload path is desired.  In
>> order to prevent the two entities from attempting to use the USB bus,
>> introduce a flag that determines when either paths are in use.
>>
>> If a PCM device is already in use, the check will return an error to
>> userspace notifying that the stream is currently busy.  This ensures that
>> only one path is using the USB substream.
>>
>> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
>> ---
>>   sound/usb/card.h                  |  1 +
>>   sound/usb/pcm.c                   | 19 +++++++++++++++++--
>>   sound/usb/qcom/qc_audio_offload.c | 15 ++++++++++++++-
> 
> should this be split in a generic part and a more specific qcom patch?
> 

Got it.

Thanks
Wesley Cheng