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

[Wesley Cheng <quic_wcheng@xxxxxxxxxxx>]

Hi Takashi,

On 2/9/2024 2:36 AM, Takashi Iwai wrote:
> 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@xxxxxxxxxxx>
>
> 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?

Sure, I'll move it into the QC offload driver.  As long as we have a 
standard API within USB SND that other vendors can also add to their 
offload drivers, I think that is sufficient.

Thanks
Wesley Cheng

> 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 */