linux-kernel - Re: [RFC PATCH 03/14] ASoC: qcom: Add USB backend ASoC driver for Q6

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Date:   Thu, 5 Jan 2023 17:05:54 -0800
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>, <broonie@...nel.org>, <lgirdwood@...il.com>,
        <andersson@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <gregkh@...uxfoundation.org>, <Thinh.Nguyen@...opsys.com>,
        <bgoswami@...cinc.com>, <tiwai@...e.com>, <robh+dt@...nel.org>,
        <agross@...nel.org>
CC:     <devicetree@...r.kernel.org>, <alsa-devel@...a-project.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <quic_jackp@...cinc.com>,
        <quic_plai@...cinc.com>
Subject: Re: [RFC PATCH 03/14] ASoC: qcom: Add USB backend ASoC driver for Q6

Hi Pierre,

On 1/4/2023 3:41 PM, Pierre-Louis Bossart wrote:
> 
>> +int q6usb_alsa_connection_cb(struct snd_soc_usb *usb, int card_idx,
>> +			int connected)
>> +{
>> +	struct snd_soc_dapm_context *dapm;
>> +	struct q6usb_port_data *data;
>> +
>> +	if (!usb->component)
>> +		return 0;
>> +
>> +	dapm = snd_soc_component_get_dapm(usb->component);
>> +	data = dev_get_drvdata(usb->component->dev);
>> +
>> +	if (connected) {
>> +		snd_soc_dapm_enable_pin(dapm, "USB_RX_BE");
>> +		/* We only track the latest USB headset plugged in */
> 
> that answers to my earlier question on how to deal with multiple
> devices, but is this a desirable policy? This could lead to a lot of
> confusion. If there are restrictions to a single device, then it might
> be more interesting for userspace or the user to indicate which USB
> device gets to use USB offload and all others use legacy.
> 

Yeah, as mentioned its still pretty open ended.  I think from the 
feedback received from Mark/Takashi, this was a viable option for now. 
Would you happen to have any insight/input on how the userspace can pass 
down that selection to the ASoC framework?  Maybe some kind of PCM IOCTL 
call?

Thanks
Wesley Cheng