linux-kernel - Re: [PATCH v15 39/50] ASoC: Introduce SND kcontrols to select sound card and PCM device

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Date: Tue, 13 Feb 2024 11:54:55 +0100
From: Takashi Iwai <tiwai@...e.de>
To: Wesley Cheng <quic_wcheng@...cinc.com>
Cc: <srinivas.kandagatla@...aro.org>,
	<mathias.nyman@...el.com>,
	<perex@...ex.cz>,
	<conor+dt@...nel.org>,
	<corbet@....net>,
	<lgirdwood@...il.com>,
	<andersson@...nel.org>,
	<krzysztof.kozlowski+dt@...aro.org>,
	<gregkh@...uxfoundation.org>,
	<Thinh.Nguyen@...opsys.com>,
	<broonie@...nel.org>,
	<bgoswami@...cinc.com>,
	<tiwai@...e.com>,
	<robh+dt@...nel.org>,
	<konrad.dybcio@...aro.org>,
	<linux-kernel@...r.kernel.org>,
	<devicetree@...r.kernel.org>,
	<linux-sound@...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 v15 39/50] ASoC: Introduce SND kcontrols to select sound card and PCM device

On Tue, 13 Feb 2024 01:54:11 +0100,
Wesley Cheng wrote:
> 
> +static int soc_usb_get_offload_dev(struct snd_kcontrol *kcontrol,
> +				   struct snd_ctl_elem_value *ucontrol)
> +{
> +	struct snd_soc_component *component = snd_kcontrol_chip(kcontrol);
> +	struct snd_soc_usb *ctx = snd_soc_usb_find_priv_data(component->dev);
> +	int ret = 0;
> +
> +	mutex_lock(&ctx_mutex);
> +	if (ctx && ctx->get_offload_dev)
> +		ret = ctx->get_offload_dev(kcontrol, ucontrol);
> +	mutex_unlock(&ctx_mutex);

It might be safer to initialize the values with -1 in case when the
callback isn't available?

>  /**
>   * snd_soc_usb_get_components_tag() - Retrieve SOC USB component tag
>   * @playback: direction of audio stream
> @@ -157,6 +218,12 @@ EXPORT_SYMBOL_GPL(snd_soc_usb_free_port);
>   */
>  int snd_soc_usb_add_port(struct snd_soc_usb *usb)
>  {
> +	int ret;
> +
> +	ret = snd_soc_usb_control_init(usb->component);
> +	if (ret < 0)
> +		return ret;
> +
>  	mutex_lock(&ctx_mutex);
>  	list_add_tail(&usb->list, &usb_ctx_list);
>  	mutex_unlock(&ctx_mutex);

We may need to remove the control element upon the driver removal,
too?  In theory, you can unload the offload stuff while snd-usb-audio
is still active.


thanks,

Takashi