Re: [PATCH v14 48/53] ALSA: usb-audio: mixer: Add USB offloading mixer control

[Takashi Iwai <tiwai@suse.de>]

On Fri, 09 Feb 2024 00:14:01 +0100,
Wesley Cheng wrote:
> 
> In order to allow userspace/applications know about USB offloading status,
> expose a sound kcontrol that fetches information about which sound card
> index is associated with the ASoC platform card supporting offloading.  In
> the USB audio offloading framework, the ASoC BE DAI link is the entity
> responsible for registering to the SOC USB layer.  SOC USB will expose more
> details about the current offloading status, which includes the USB sound
> card and USB PCM device indexes currently being used.
> 
> Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>

Now looking at this again, I noticed that this will bring the
hard-dependency on ASoC stuff to USB-audio driver, since it adds the
call of snd_soc_usb_device_offload_available().

Maybe we can let the add-on platform adding/removing the control
element on the fly instead?


thanks,

Takashi

> ---
>  sound/usb/Kconfig             |  4 ++
>  sound/usb/Makefile            |  1 +
>  sound/usb/mixer.c             |  5 +++
>  sound/usb/mixer_usb_offload.c | 72 +++++++++++++++++++++++++++++++++++
>  sound/usb/mixer_usb_offload.h | 17 +++++++++
>  5 files changed, 99 insertions(+)
>  create mode 100644 sound/usb/mixer_usb_offload.c
>  create mode 100644 sound/usb/mixer_usb_offload.h
> 
> diff --git a/sound/usb/Kconfig b/sound/usb/Kconfig
> index 4c842fbe6365..3e7be258d0e3 100644
> --- a/sound/usb/Kconfig
> +++ b/sound/usb/Kconfig
> @@ -176,10 +176,14 @@ config SND_BCD2000
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called snd-bcd2000.
>  
> +config SND_USB_OFFLOAD_MIXER
> +	bool
> +
>  config SND_USB_AUDIO_QMI
>  	tristate "Qualcomm Audio Offload driver"
>  	depends on QCOM_QMI_HELPERS && SND_USB_AUDIO && USB_XHCI_SIDEBAND
>  	select SND_PCM
> +	select SND_USB_OFFLOAD_MIXER
>  	help
>  	  Say Y here to enable the Qualcomm USB audio offloading feature.
>  
> diff --git a/sound/usb/Makefile b/sound/usb/Makefile
> index 246788268ddd..8c54660a11b0 100644
> --- a/sound/usb/Makefile
> +++ b/sound/usb/Makefile
> @@ -22,6 +22,7 @@ snd-usb-audio-objs := 	card.o \
>  			stream.o \
>  			validate.o
>  
> +snd-usb-audio-$(CONFIG_SND_USB_OFFLOAD_MIXER) += mixer_usb_offload.o
>  snd-usb-audio-$(CONFIG_SND_USB_AUDIO_MIDI_V2) += midi2.o
>  snd-usb-audio-$(CONFIG_SND_USB_AUDIO_USE_MEDIA_CONTROLLER) += media.o
>  
> diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
> index 409fc1164694..09229e623469 100644
> --- a/sound/usb/mixer.c
> +++ b/sound/usb/mixer.c
> @@ -48,6 +48,7 @@
>  #include "mixer.h"
>  #include "helper.h"
>  #include "mixer_quirks.h"
> +#include "mixer_usb_offload.h"
>  #include "power.h"
>  
>  #define MAX_ID_ELEMS	256
> @@ -3609,6 +3610,10 @@ int snd_usb_create_mixer(struct snd_usb_audio *chip, int ctrlif)
>  	if (err < 0)
>  		goto _error;
>  
> +	err = snd_usb_offload_init_mixer(mixer);
> +	if (err < 0)
> +		goto _error;
> +
>  	err = snd_device_new(chip->card, SNDRV_DEV_CODEC, mixer, &dev_ops);
>  	if (err < 0)
>  		goto _error;
> diff --git a/sound/usb/mixer_usb_offload.c b/sound/usb/mixer_usb_offload.c
> new file mode 100644
> index 000000000000..61b17359b987
> --- /dev/null
> +++ b/sound/usb/mixer_usb_offload.c
> @@ -0,0 +1,72 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2022-2024 Qualcomm Innovation Center, Inc. All rights reserved.
> + */
> +
> +#include <linux/usb.h>
> +
> +#include <sound/core.h>
> +#include <sound/control.h>
> +#include <sound/soc-usb.h>
> +
> +#include "card.h"
> +#include "mixer.h"
> +#include "mixer_usb_offload.h"
> +#include "usbaudio.h"
> +
> +static int
> +snd_usb_offload_create_mixer(struct usb_mixer_interface *mixer,
> +		       const struct snd_kcontrol_new *new_kctl)
> +{
> +	struct snd_usb_audio *chip = mixer->chip;
> +	struct usb_device *udev = chip->dev;
> +
> +	return snd_ctl_add(chip->card,
> +			   snd_ctl_new1(new_kctl, udev->bus->sysdev));
> +}
> +
> +static int
> +snd_usb_offload_available_get(struct snd_kcontrol *kcontrol,
> +		      struct snd_ctl_elem_value *ucontrol)
> +{
> +	struct device *sysdev = snd_kcontrol_chip(kcontrol);
> +	int ret;
> +
> +	ret = snd_soc_usb_device_offload_available(sysdev);
> +	ucontrol->value.integer.value[0] = ret < 0 ? -1 : ret;
> +
> +	return ret < 0 ? ret : 0;
> +}
> +
> +static int snd_usb_offload_available_info(struct snd_kcontrol *kcontrol,
> +			      struct snd_ctl_elem_info *uinfo)
> +{
> +	uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
> +	uinfo->count = 1;
> +	uinfo->value.integer.min = -1;
> +	uinfo->value.integer.max = SNDRV_CARDS;
> +
> +	return 0;
> +}
> +
> +static const struct snd_kcontrol_new snd_usb_offload_available_ctl = {
> +	.iface = SNDRV_CTL_ELEM_IFACE_CARD,
> +	.access = SNDRV_CTL_ELEM_ACCESS_READ,
> +	.name = "USB Offload Playback Capable Card",
> +	.info = snd_usb_offload_available_info,
> +	.get = snd_usb_offload_available_get,
> +};
> +
> +/**
> + * snd_usb_offload_init_mixer() - Add USB offload bounded mixer
> + * @mixer - USB mixer
> + *
> + * Creates a sound control for a USB audio device, so that applications can
> + * query for if there is an available USB audio offload path, and which
> + * card is managing it.
> + */
> +int snd_usb_offload_init_mixer(struct usb_mixer_interface *mixer)
> +{
> +	return snd_usb_offload_create_mixer(mixer, &snd_usb_offload_available_ctl);
> +}
> +EXPORT_SYMBOL_GPL(snd_usb_offload_init_mixer);
> diff --git a/sound/usb/mixer_usb_offload.h b/sound/usb/mixer_usb_offload.h
> new file mode 100644
> index 000000000000..fb88e872d8fa
> --- /dev/null
> +++ b/sound/usb/mixer_usb_offload.h
> @@ -0,0 +1,17 @@
> +/* SPDX-License-Identifier: GPL-2.0
> + *
> + * Copyright (c) 2022-2024 Qualcomm Innovation Center, Inc. All rights reserved.
> + */
> +
> +#ifndef __USB_OFFLOAD_MIXER_H
> +#define __USB_OFFLOAD_MIXER_H
> +
> +#if IS_ENABLED(CONFIG_SND_USB_OFFLOAD_MIXER)
> +int snd_usb_offload_init_mixer(struct usb_mixer_interface *mixer);
> +#else
> +static int snd_usb_offload_init_mixer(struct usb_mixer_interface *mixer)
> +{
> +	return 0;
> +}
> +#endif
> +#endif /* __USB_OFFLOAD_MIXER_H */