linux-kernel - Re: [PATCH v7 29/33] ASoC: qcom: qdsp6: Add SND kcontrol for fetching offload status

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Message-ID: <191e6429-bb47-625b-a074-fa67ee052f03@quicinc.com>
Date:   Wed, 27 Sep 2023 13:10:40 -0700
From:   Wesley Cheng <quic_wcheng@...cinc.com>
To:     Mark Brown <broonie@...nel.org>
CC:     <mathias.nyman@...el.com>, <gregkh@...uxfoundation.org>,
        <lgirdwood@...il.com>, <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>, <linux-kernel@...r.kernel.org>,
        <linux-usb@...r.kernel.org>, <alsa-devel@...a-project.org>,
        <linux-arm-msm@...r.kernel.org>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH v7 29/33] ASoC: qcom: qdsp6: Add SND kcontrol for fetching
 offload status

Hi Mark,

On 9/27/2023 8:02 AM, Mark Brown wrote:
> On Thu, Sep 21, 2023 at 02:48:39PM -0700, Wesley Cheng wrote:
> 
>> Add a kcontrol to the platform sound card to fetch the current offload
>> status.  This can allow for userspace to ensure/check which USB SND
>> resources are actually busy versus having to attempt opening the USB SND
>> devices, which will result in an error if offloading is active.
> 
>> +static int q6usb_prepare(struct snd_pcm_substream *substream,
>> +               struct snd_soc_dai *dai)
>> +{
>> +       struct q6usb_port_data *data = dev_get_drvdata(dai->dev);
>> +
>> +       mutex_lock(&data->mutex);
>> +       data->status[data->sel_card_idx].running = true;
>> +       mutex_unlock(&data->mutex);
> 
> These updates of running should really have a snd_ctl_notify() so that
> UIs can know to update when the value changes while they're open.
> 

Sure, me review some of the APIs again and add the notify call where 
necessary.

>> +static int q6usb_mixer_get_offload_status(struct snd_kcontrol *kcontrol,
>> +				   struct snd_ctl_elem_value *ucontrol)
>> +{
> 
>> +	running = q6usb_find_running(data);
>> +	if (running < 0) {
>> +		card_idx = -1;
>> +		pcm_idx = -1;
>> +	} else {
>> +		card_idx = running;
>> +		pcm_idx = data->status[running].pcm_index;
>> +	}
>> +
>> +	ucontrol->value.integer.value[0] = card_idx;
>> +	ucontrol->value.integer.value[1] = pcm_idx;
> 
> This feels a bit messy but I'm not sure what we'd do that's better so
> unless someone else has better ideas let's go with this.  Possibly we
> should standardise this as a new control type for joining cards up so at
> least if there's further needs for this we can use the same solution?

I'm all ears for any suggestions from other users :).  I think its a bit 
difficult to tell since this is the first iteration of adding this 
feature.  Pierre gave me some great feedback from the 
userspace/application level, and tried my best to accommodate for those 
requirements since it would be the main entity interacting with these 
controls.

Thanks
Wesley Cheng