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

[Wesley Cheng]

Hi Pierre,

On 7/25/2023 1:59 AM, Pierre-Louis Bossart wrote:
> 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@xxxxxxxxxxx>
> > ---
> >   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.

chip_idx is the index to the USB SND chip array which carries 
information about each udev (USB device) connected to USB SND)

> 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.

I agree.  My plan is to address this by having another SND SOC USB 
structure that is created by the USB class driver, ie qc_usb_offload, 
which would populate the required parameters.

Main thing I wanted to avoid is to have to expose the main USB SND 
structure if we're only going to only have a few variables to check for.

> >   	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?

Idea was just to have a bitmapped value of all offload capable audio 
devices that are currently connected.  Then we can take the necessary 
actions when everything has been disconnected.

> > +	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.

I will add comments, but it basically will populate some of the limits 
that we'll end up using for controlling the ksndcontrols.

Thanks
Wesley Cheng