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

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Message-ID: <ZRRD8eFZugh/+dex@finisterre.sirena.org.uk>
Date:   Wed, 27 Sep 2023 17:02:09 +0200
From:   Mark Brown <broonie@...nel.org>
To:     Wesley Cheng <quic_wcheng@...cinc.com>
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

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.

> +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?

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