Re: [PATCH v9 29/34] ASoC: qcom: qdsp6: Add SND kcontrol to select offload device

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 10/17/23 15:01, Wesley Cheng wrote:
> Expose a kcontrol on the platform sound card, which will allow for
> userspace to determine which USB card number and PCM device to offload.
> This allows for userspace to potentially tag an alternate path for a
> specific USB SND card and PCM device.  Previously, control was absent, and
> the offload path would be enabled on the last USB SND device which was
> connected.  This logic will continue to be applicable if no mixer input is
> received for specific device selection.
> 
> An example to configure the offload device using tinymix:
> tinymix -D 0 set 'Q6USB offload SND device select' 1 0
> 
> The above will set the Q6AFE device token to choose offload on card#1 and
> pcm#0.  Device selection is made possible by setting the Q6AFE device
> token.  The audio DSP utilizes this parameter, and will pass this field
> back to the USB offload driver within the QMI stream requests.

This still begs the question on how userspace would figure what the
card1 is and which endpoint is used when PCM0 is opened?

Ideally userpace would not have to know anything about "Q6USB".
Presumably when other vendors expose their USB offload solution, we
would want a generic control name, no?

Jaroslav should chime in on this one :-)


> Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
> ---
>  sound/soc/qcom/qdsp6/q6usb.c | 125 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 122 insertions(+), 3 deletions(-)
> 
> diff --git a/sound/soc/qcom/qdsp6/q6usb.c b/sound/soc/qcom/qdsp6/q6usb.c
> index d697cbe7f184..a95276b7d91d 100644
> --- a/sound/soc/qcom/qdsp6/q6usb.c
> +++ b/sound/soc/qcom/qdsp6/q6usb.c
> @@ -14,6 +14,7 @@
>  #include <linux/dma-map-ops.h>
>  
>  #include <sound/pcm.h>
> +#include <sound/control.h>
>  #include <sound/soc.h>
>  #include <sound/soc-usb.h>
>  #include <sound/pcm_params.h>
> @@ -35,9 +36,12 @@ struct q6usb_port_data {
>  	struct q6afe_usb_cfg usb_cfg;
>  	struct snd_soc_usb *usb;
>  	struct q6usb_offload priv;
> +	struct mutex mutex;

missing comment on what this protects. "mutex" is really a poor
choice/name if I am honest.

>  	unsigned long available_card_slot;
>  	struct q6usb_status status[SNDRV_CARDS];
> -	int active_idx;
> +	bool idx_valid;
> +	int sel_card_idx;
> +	int sel_pcm_idx;
>  };

> +/* Build a mixer control for a UAC connector control (jack-detect) */
> +static void q6usb_connector_control_init(struct snd_soc_component *component)
> +{
> +	int ret;
> +
> +	ret = snd_ctl_add(component->card->snd_card,
> +				snd_ctl_new1(&q6usb_offload_dev_ctrl, component));
> +	if (ret < 0)
> +		return;

that error handling does not seem terribly useful...

> +}
> +
>  static int q6usb_audio_ports_of_xlate_dai_name(struct snd_soc_component *component,
>  					const struct of_phandle_args *args,
>  					const char **dai_name)
> @@ -115,9 +227,11 @@ static int q6usb_alsa_connection_cb(struct snd_soc_usb *usb,
>  
>  	data = dev_get_drvdata(usb->component->dev);
>  
> +	mutex_lock(&data->mutex);
>  	if (connected) {
>  		/* We only track the latest USB headset plugged in */
> -		data->active_idx = sdev->card_idx;
> +		if (!data->idx_valid || data->sel_card_idx < 0)
> +			data->sel_card_idx = sdev->card_idx;
>  
>  		set_bit(sdev->card_idx, &data->available_card_slot);
>  		data->status[sdev->card_idx].num_pcm = sdev->num_playback;
> @@ -127,6 +241,7 @@ static int q6usb_alsa_connection_cb(struct snd_soc_usb *usb,
>  		data->status[sdev->card_idx].num_pcm = 0;
>  		data->status[sdev->card_idx].chip_index = 0;
>  	}
> +	mutex_unlock(&data->mutex);
>  
>  	return 0;
>  }
> @@ -135,6 +250,8 @@ static int q6usb_component_probe(struct snd_soc_component *component)
>  {
>  	struct q6usb_port_data *data = dev_get_drvdata(component->dev);
>  
> +	q6usb_connector_control_init(component);
> +
>  	data->usb = snd_soc_usb_add_port(component->dev, &data->priv, q6usb_alsa_connection_cb);
>  	if (IS_ERR(data->usb)) {
>  		dev_err(component->dev, "failed to add usb port\n");
> @@ -189,6 +306,8 @@ static int q6usb_dai_dev_probe(struct platform_device *pdev)
>  
>  	data->priv.domain = iommu_get_domain_for_dev(&pdev->dev);
>  
> +	mutex_init(&data->mutex);
> +
>  	data->priv.dev = dev;
>  	dev_set_drvdata(dev, data);
>