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

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Message-ID: <654077f4-2ae2-3457-b777-9eb3b816c6ba@linux.intel.com>
Date:   Fri, 6 Jan 2023 10:16:09 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Wesley Cheng <quic_wcheng@...cinc.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



On 1/5/23 19:05, Wesley Cheng wrote:
> 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?

I don't have a turn-key solution either :-)
We'd need userspace to make one device as 'preferred' or 'optimized' and
give it a priority somehow. It can't be a PCM IOCTL, it has to be at the
device level.

It's really a second-level optimization that can be parked for now, the
bulk of the work is really the interaction between USB audio and ASoC
stacks, we should probably focus on that BIG topic with a design that
can be shared across implementations.