linux-kernel - Re: [PATCH v26 28/33] ALSA: usb-audio: qcom: Introduce QC USB SND offloading support

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Message-ID: <8a5be3be-7097-4258-a5a4-7ab440823968@quicinc.com>
Date: Tue, 3 Sep 2024 16:41:10 -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>, <dmitry.torokhov@...il.com>,
        <corbet@....net>, <broonie@...nel.org>, <lgirdwood@...il.com>,
        <tiwai@...e.com>, <krzk+dt@...nel.org>, <Thinh.Nguyen@...opsys.com>,
        <bgoswami@...cinc.com>, <robh@...nel.org>,
        <gregkh@...uxfoundation.org>
CC: <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-sound@...r.kernel.org>, <linux-input@...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 v26 28/33] ALSA: usb-audio: qcom: Introduce QC USB SND
 offloading support

Hi Pierre,

On 8/30/2024 2:52 AM, Pierre-Louis Bossart wrote:
>> +/* Stream disable request timeout during USB device disconnect */
>> +#define DEV_RELEASE_WAIT_TIMEOUT 10000 /* in ms */
> 10s really? That seems rather large for a stream disable timeout...

Hmm, yes that is overkill, will adjust it accordingly.


>> +static struct snd_usb_platform_ops offload_ops = {
>> +	.connect_cb = qc_usb_audio_offload_probe,
>> +	.disconnect_cb = qc_usb_audio_offload_disconnect,
>> +	.suspend_cb = qc_usb_audio_offload_suspend,
>> +};
> You probably want to explain why there's no .resume_cb?
>
> The comments mention also that the suspend_cb has to stop playback, but
> then who resumes playback :-)
>
I can add a comment.  Ideally, the suspend_cb is only used for the case of PM suspend/system suspend.  If usb autosuspend is enabled, then the QC offload driver will handle the voting based on the audio stream being active or not.  Is there a use case where the ASoC layer re-opens any previously active audio streams so that userspace doesn't have to?  Currently, I was under the assumption that the audio stream would have to be re-opened by the application.

Thanks

Wesley Cheng