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

[Wesley Cheng <quic_wcheng@quicinc.com>]

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@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?
> 

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 */