Hi Pierre,
On 8/30/2024 3:05 AM, Pierre-Louis Bossart wrote:
>
> On 8/29/24 21:41, 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
>> and PCM index the USB device is mapped to for supporting offloading. In
>> the USB audio offloading framework, the ASoC BE DAI link is the entity
>> responsible for registering to the SOC USB layer.
>>
>> It is expected for the USB SND offloading driver to add the kcontrol to the
>> sound card associated with the USB audio device. An example output would
>> look like:
> this is very odd, the offloading driver adds a control to another card?
>
> That seems like a rather important layering violation.
>
> I thought it was done the other way, the USB audio card created a
> control that would point to the other card/device.
The USB SND offloading vendor driver (qc_audio_offload), which technically co-exists with USB SND core, is the entity that will add the offload kcontrol to the USB audio device's sound card. Initially, I had the kcontrol creation as part of the USB SND mixer, but I believe Takashi preferred if the vendor driver did it instead.
>
>> tinymix -D 1 get 'USB Offload Playback Route PCM#0'
>> -1, -1 (range -1->255)
>>
>> This example signifies that there is no mapped ASoC path available for the
>> USB SND device.
> but that control would not even exist if the ASoC-based driver isn't probed.
>
> It's become really hard to follow, I've been on all this for 1.5hrs and
> losing track of the design.
Hence why it probably is a good idea to leave it within the USB offload vendor driver. There are checks to ensure that the ASoC based driver is probed/available before the kcontrols are created for a device. If there are devices that were identified before the ASoC components were probed, then the snd_usb_rediscover_devices() is triggered as part of soc-usb, and that would call the connect_cb() callback to the USB SND vendor offload driver to create the kcontrol.
Thanks
Wesley Cheng
>> tinymix -D 1 get 'USB Offload Playback Route PCM#0'
>> 0, 0 (range -1->255)
>>
>> This example signifies that the offload path is available over ASoC sound
>> card index#0 and PCM device#0.
>>
>> Signed-off-by: Wesley Cheng <quic_wcheng@xxxxxxxxxxx>
>> ---
>> sound/usb/Kconfig | 10 +++
>> sound/usb/Makefile | 2 +
>> sound/usb/mixer_usb_offload.c | 102 ++++++++++++++++++++++++++++++
>> sound/usb/mixer_usb_offload.h | 17 +++++
>> sound/usb/qcom/Makefile | 2 +-
>> sound/usb/qcom/qc_audio_offload.c | 2 +
>> 6 files changed, 134 insertions(+), 1 deletion(-)
>> 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 5cc3eaf53e6b..e3fbf9541d0b 100644
>> --- a/sound/usb/Kconfig
>> +++ b/sound/usb/Kconfig
>> @@ -176,10 +176,20 @@ 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
>> + tristate "USB Audio Offload mixer control"
>> + help
>> + Say Y to enable the USB audio offloading mixer controls. This
>> + exposes an USB offload capable kcontrol to signal to applications
>> + about which platform sound card can support USB audio offload.
>> + The returning values specify the mapped ASoC card and PCM device
>> + the USB audio device is associated to.
>> +
>> config SND_USB_AUDIO_QMI
>> tristate "Qualcomm Audio Offload driver"
>> depends on QCOM_QMI_HELPERS && SND_USB_AUDIO && USB_XHCI_SIDEBAND && SND_SOC_USB
>> 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 54a06a2f73ca..2f19f854944c 100644
>> --- a/sound/usb/Makefile
>> +++ b/sound/usb/Makefile
>> @@ -36,3 +36,5 @@ obj-$(CONFIG_SND_USB_US122L) += snd-usbmidi-lib.o
>>
>> obj-$(CONFIG_SND) += misc/ usx2y/ caiaq/ 6fire/ hiface/ bcd2000/ qcom/
>> obj-$(CONFIG_SND_USB_LINE6) += line6/
>> +
>> +obj-$(CONFIG_SND_USB_OFFLOAD_MIXER) += mixer_usb_offload.o
>> diff --git a/sound/usb/mixer_usb_offload.c b/sound/usb/mixer_usb_offload.c
>> new file mode 100644
>> index 000000000000..16e2fd634684
>> --- /dev/null
>> +++ b/sound/usb/mixer_usb_offload.c
>> @@ -0,0 +1,102 @@
>> +// 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 "usbaudio.h"
>> +#include "card.h"
>> +#include "helper.h"
>> +#include "mixer.h"
>> +
>> +#include "mixer_usb_offload.h"
>> +
>> +#define PCM_IDX(n) ((n) & 0xffff)
>> +#define CARD_IDX(n) ((n) >> 16)
>> +
>> +static int
>> +snd_usb_offload_route_get(struct snd_kcontrol *kcontrol,
>> + struct snd_ctl_elem_value *ucontrol)
>> +{
>> + struct device *sysdev = snd_kcontrol_chip(kcontrol);
>> + int ret;
>> +
>> + ret = snd_soc_usb_update_offload_route(sysdev,
>> + CARD_IDX(kcontrol->private_value),
>> + PCM_IDX(kcontrol->private_value),
>> + SNDRV_PCM_STREAM_PLAYBACK,
>> + ucontrol->value.integer.value);
>> + if (ret < 0) {
>> + ucontrol->value.integer.value[0] = -1;
>> + ucontrol->value.integer.value[1] = -1;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static int snd_usb_offload_route_info(struct snd_kcontrol *kcontrol,
>> + struct snd_ctl_elem_info *uinfo)
>> +{
>> + uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
>> + uinfo->count = 2;
>> + uinfo->value.integer.min = -1;
>> + /* Arbitrary max value, as there is no 'limit' on number of PCM devices */
>> + uinfo->value.integer.max = 0xff;
>> +
>> + return 0;
>> +}
>> +
>> +static struct snd_kcontrol_new snd_usb_offload_mapped_ctl = {
>> + .iface = SNDRV_CTL_ELEM_IFACE_CARD,
>> + .access = SNDRV_CTL_ELEM_ACCESS_READ,
>> + .info = snd_usb_offload_route_info,
>> + .get = snd_usb_offload_route_get,
>> +};
>> +
>> +/**
>> + * snd_usb_offload_create_ctl() - Add USB offload bounded mixer
>> + * @chip - USB SND chip device
>> + *
>> + * 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_create_ctl(struct snd_usb_audio *chip)
>> +{
>> + struct usb_device *udev = chip->dev;
>> + struct snd_kcontrol_new *chip_kctl;
>> + struct snd_usb_substream *subs;
>> + struct snd_usb_stream *as;
>> + char ctl_name[37];
>> + int ret;
>> +
>> + list_for_each_entry(as, &chip->pcm_list, list) {
>> + subs = &as->substream[SNDRV_PCM_STREAM_PLAYBACK];
>> + if (!subs->ep_num)
>> + continue;
>> +
>> + chip_kctl = &snd_usb_offload_mapped_ctl;
>> + chip_kctl->count = 1;
>> + /*
>> + * Store the associated USB SND card number and PCM index for
>> + * the kctl.
>> + */
>> + chip_kctl->private_value = as->pcm_index |
>> + chip->card->number << 16;
>> + sprintf(ctl_name, "USB Offload Playback Route PCM#%d",
>> + as->pcm_index);
>> + chip_kctl->name = ctl_name;
>> + ret = snd_ctl_add(chip->card, snd_ctl_new1(chip_kctl,
>> + udev->bus->sysdev));
>> + if (ret < 0)
>> + break;
>> + }
>> +
>> + return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(snd_usb_offload_create_ctl);
>> diff --git a/sound/usb/mixer_usb_offload.h b/sound/usb/mixer_usb_offload.h
>> new file mode 100644
>> index 000000000000..3f6e2a8b19c8
>> --- /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_create_ctl(struct snd_usb_audio *chip);
>> +#else
>> +static inline int snd_usb_offload_create_ctl(struct snd_usb_audio *chip)
>> +{
>> + return 0;
>> +}
>> +#endif
>> +#endif /* __USB_OFFLOAD_MIXER_H */
>> diff --git a/sound/usb/qcom/Makefile b/sound/usb/qcom/Makefile
>> index a81c9b28d484..4005e8391ab9 100644
>> --- a/sound/usb/qcom/Makefile
>> +++ b/sound/usb/qcom/Makefile
>> @@ -1,2 +1,2 @@
>> snd-usb-audio-qmi-objs := usb_audio_qmi_v01.o qc_audio_offload.o
>> -obj-$(CONFIG_SND_USB_AUDIO_QMI) += snd-usb-audio-qmi.o
>> \ No newline at end of file
>> +obj-$(CONFIG_SND_USB_AUDIO_QMI) += snd-usb-audio-qmi.o
>> diff --git a/sound/usb/qcom/qc_audio_offload.c b/sound/usb/qcom/qc_audio_offload.c
>> index a7ad15404fd1..5b9262a116be 100644
>> --- a/sound/usb/qcom/qc_audio_offload.c
>> +++ b/sound/usb/qcom/qc_audio_offload.c
>> @@ -36,6 +36,7 @@
>> #include "../helper.h"
>> #include "../pcm.h"
>> #include "../power.h"
>> +#include "../mixer_usb_offload.h"
>>
>> #include "usb_audio_qmi_v01.h"
>>
>> @@ -1703,6 +1704,7 @@ static void qc_usb_audio_offload_probe(struct snd_usb_audio *chip)
>> sdev->card_idx = chip->card->number;
>> sdev->chip_idx = chip->index;
>>
>> + snd_usb_offload_create_ctl(chip);
>> snd_soc_usb_connect(usb_get_usb_backend(udev), sdev);
>> }
>>
