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.
>
> 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.
> 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);
> }
>
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