linux-kernel - Re: [PATCH v38 26/31] ASoC: qcom: qdsp6: Fetch USB offload mapped card and PCM device

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Message-ID: <Z_doJMXjSFHt6eAp@linaro.org>
Date: Thu, 10 Apr 2025 08:41:40 +0200
From: Stephan Gerhold <stephan.gerhold@...aro.org>
To: Wesley Cheng <quic_wcheng@...cinc.com>
Cc: srinivas.kandagatla@...aro.org, mathias.nyman@...el.com, perex@...ex.cz,
	conor+dt@...nel.org, dmitry.torokhov@...il.com, corbet@....net,
	broonie@...nel.org, lgirdwood@...il.com, robh@...nel.org,
	krzk+dt@...nel.org, pierre-louis.bossart@...ux.intel.com,
	Thinh.Nguyen@...opsys.com, tiwai@...e.com,
	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, linux-sound@...r.kernel.org,
	linux-input@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v38 26/31] ASoC: qcom: qdsp6: Fetch USB offload mapped
 card and PCM device

On Wed, Apr 09, 2025 at 12:47:59PM -0700, Wesley Cheng wrote:
> The USB SND path may need to know how the USB offload path is routed, so
> that applications can open the proper sound card and PCM device.  The
> implementation for the QC ASoC design has a "USB Mixer" kcontrol for each

Is this "USB_RX Audio Mixer" now?

> possible FE (Q6ASM) DAI, which can be utilized to know which front end link
> is enabled.
> 
> When an application/userspace queries for the mapped offload devices, the
> logic will lookup the USB mixer status though the following path:
> 
> MultiMedia* <-> MM_DL* <-> USB Mixer*

^

> 
> The "USB Mixer" is a DAPM widget, and the q6routing entity will set the

^

> DAPM connect status accordingly if the USB mixer is enabled.  If enabled,
> the Q6USB backend link can fetch the PCM device number from the FE DAI
> link (Multimedia*).  With respects to the card number, that is
> straightforward, as the ASoC components have direct references to the ASoC
> platform sound card.
> 
> An example output can be shown below:
> 
> Number of controls: 9
> name                                    value
> Capture Channel Map                     0, 0 (range 0->36)
> Playback Channel Map                    0, 0 (range 0->36)
> Headset Capture Switch                  On
> Headset Capture Volume                  1 (range 0->4)
> Sidetone Playback Switch                On
> Sidetone Playback Volume                4096 (range 0->8192)
> Headset Playback Switch                 On
> Headset Playback Volume                 20, 20 (range 0->24)
> USB Offload Playback Route PCM#0        0, 1 (range -1->255)
> 
> The "USB Offload Playback Route PCM#*" kcontrol will signify the
> corresponding card and pcm device it is offload to. (card#0 pcm - device#1)
> If the USB SND device supports multiple audio interfaces, then it will
> contain several PCM streams, hence in those situations, it is expected
> that there will be multiple playback route kcontrols created.
> 
> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
> ---
>  sound/soc/qcom/qdsp6/q6usb.c | 98 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 98 insertions(+)
> 
> diff --git a/sound/soc/qcom/qdsp6/q6usb.c b/sound/soc/qcom/qdsp6/q6usb.c
> index 6634e132787e..274c251e84dd 100644
> --- a/sound/soc/qcom/qdsp6/q6usb.c
> +++ b/sound/soc/qcom/qdsp6/q6usb.c
> @@ -134,6 +134,103 @@ static int q6usb_audio_ports_of_xlate_dai_name(struct snd_soc_component *compone
>  	return ret;
>  }
>  
> +static int q6usb_get_pcm_id_from_widget(struct snd_soc_dapm_widget *w)
> +{
> +	struct snd_soc_pcm_runtime *rtd;
> +	struct snd_soc_dai *dai;
> +
> +	for_each_card_rtds(w->dapm->card, rtd) {
> +		dai = snd_soc_rtd_to_cpu(rtd, 0);
> +		/*
> +		 * Only look for playback widget. RTD number carries the assigned
> +		 * PCM index.
> +		 */
> +		if (dai->stream[0].widget == w)
> +			return rtd->id;
> +	}
> +
> +	return -1;
> +}
> +
> +static int q6usb_usb_mixer_enabled(struct snd_soc_dapm_widget *w)
> +{
> +	struct snd_soc_dapm_path *p;
> +
> +	/* Checks to ensure USB path is enabled/connected */
> +	snd_soc_dapm_widget_for_each_sink_path(w, p)
> +		if (!strcmp(p->sink->name, "USB Mixer") && p->connect)
> +			return 1;

I assume this also needs to be changed. Please make sure you test the
series again. :)

> +
> +	return 0;
> +}
> +
> +static int q6usb_get_pcm_id(struct snd_soc_component *component)
> +{
> +	struct snd_soc_dapm_widget *w;
> +	struct snd_soc_dapm_path *p;
> +	int pidx;
> +
> +	/*
> +	 * Traverse widgets to find corresponding FE widget.  The DAI links are
> +	 * built like the following:
> +	 *    MultiMedia* <-> MM_DL* <-> USB Mixer*

^

Thanks,
Stephan