[v30,28/30] ALSA: usb-audio: Add USB offload route kcontrol

diff --git a/sound/usb/Kconfig b/sound/usb/Kconfig
index d0f65311894f..4994e6261be5 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_SEC_INTR && 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..e0689a3b9b86
--- /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[34];
+	int ret;
+
+	list_for_each_entry(as, &chip->pcm_list, list) {
+		subs = &as->substream[SNDRV_PCM_STREAM_PLAYBACK];
+		if (!subs->ep_num || as->pcm_index > 0xff)
+			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 9e1c94d28461..f78cd8c504b9 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"
 
@@ -1709,6 +1710,7 @@  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);
 	}