linux-kernel - Re: [PATCH v4 26/32] sound: Pass USB SND card and PCM information to SOC USB

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Date:   Tue, 25 Jul 2023 10:59:31 +0200
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Wesley Cheng <quic_wcheng@...cinc.com>, agross@...nel.org,
        andersson@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        catalin.marinas@....com, will@...nel.org, mathias.nyman@...el.com,
        gregkh@...uxfoundation.org, lgirdwood@...il.com,
        broonie@...nel.org, perex@...ex.cz, tiwai@...e.com,
        srinivas.kandagatla@...aro.org, bgoswami@...cinc.com,
        Thinh.Nguyen@...opsys.com
Cc:     linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-usb@...r.kernel.org, alsa-devel@...a-project.org,
        quic_jackp@...cinc.com, oneukum@...e.com, albertccwang@...gle.com,
        o-takashi@...amocchi.jp
Subject: Re: [PATCH v4 26/32] sound: Pass USB SND card and PCM information to
 SOC USB



On 7/25/23 04:34, Wesley Cheng wrote:
> Currently, only the index to the USB SND card array is passed to the USB
> backend.  Pass through more information, specifically the USB SND card
> number and the number of PCM devices available.  The USB backend should
> know about which sound resources are being shared between the ASoC and USB
> SND paths.  This can be utilized to properly select and maintain the
> offloading devices.
> 
> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
> ---
>  include/sound/soc-usb.h           |  9 +++++----
>  sound/soc/qcom/qdsp6/q6usb.c      | 20 ++++++++++++++++++--
>  sound/soc/soc-usb.c               | 12 +++++++-----
>  sound/usb/qcom/qc_audio_offload.c |  9 +++++----
>  4 files changed, 35 insertions(+), 15 deletions(-)
> 
> diff --git a/include/sound/soc-usb.h b/include/sound/soc-usb.h
> index 71e6e75e600a..606128332044 100644
> --- a/include/sound/soc-usb.h
> +++ b/include/sound/soc-usb.h
> @@ -19,20 +19,21 @@ struct snd_soc_usb {
>  	struct device *dev;
>  	struct snd_soc_component *component;
>  	int (*connection_status_cb)(struct snd_soc_usb *usb, int card_idx,
> -				int connected);
> +				int chip_idx, int num_pcm, int connected);

I don't know what 'chip_idx' is.

The 'num_pcm' sounds problematic if there are different devices for
playback and capture. I would guess this is for playback only, but this
doesn't scale.

>  	void *priv_data;
>  };

> +struct q6usb_status {
> +	unsigned int num_pcm;
> +	unsigned int chip_index;
> +	unsigned int pcm_index;
> +};
> +
>  struct q6usb_port_data {
>  	struct q6afe_usb_cfg usb_cfg;
>  	struct snd_soc_usb *usb;
>  	struct q6usb_offload priv;
> +	unsigned long available_card_slot;

what is a card slot?

> +	struct q6usb_status status[SNDRV_CARDS];
>  	int active_idx;
>  };
>  
> @@ -97,7 +105,7 @@ static int q6usb_audio_ports_of_xlate_dai_name(struct snd_soc_component *compone
>  }
>  
>  static int q6usb_alsa_connection_cb(struct snd_soc_usb *usb, int card_idx,
> -			int connected)
> +			int chip_idx, int num_pcm, int connected)
>  {
>  	struct snd_soc_dapm_context *dapm;
>  	struct q6usb_port_data *data;
> @@ -109,8 +117,16 @@ static int q6usb_alsa_connection_cb(struct snd_soc_usb *usb, int card_idx,
>  		snd_soc_dapm_enable_pin(dapm, "USB_RX_BE");
>  		/* We only track the latest USB headset plugged in */
>  		data->active_idx = card_idx;
> +
> +		set_bit(card_idx, &data->available_card_slot);
> +		data->status[card_idx].num_pcm = num_pcm;
> +		data->status[card_idx].chip_index = chip_idx;
>  	} else {
> -		snd_soc_dapm_disable_pin(dapm, "USB_RX_BE");
> +		clear_bit(card_idx, &data->available_card_slot);
> +		data->status[card_idx].num_pcm = 0;
> +		data->status[card_idx].chip_index = 0;
> +		if (!data->available_card_slot)
> +			snd_soc_dapm_disable_pin(dapm, "USB_RX_BE");

not able to follow what this does, this patch is rather unclear and
lacks comments.

>  	}
>  	snd_soc_dapm_sync(dapm);