[v29,15/33] ASoC: Add SOC USB APIs for adding an USB backend

diff --git a/include/sound/soc-usb.h b/include/sound/soc-usb.h
new file mode 100644
index 000000000000..34240321bbca
--- /dev/null
+++ b/include/sound/soc-usb.h
@@ -0,0 +1,97 @@ 
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * Copyright (c) 2022-2024 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#ifndef __LINUX_SND_SOC_USB_H
+#define __LINUX_SND_SOC_USB_H
+
+#include <sound/soc.h>
+
+/**
+ * struct snd_soc_usb_device
+ * @card_idx - sound card index associated with USB device
+ * @chip_idx - USB sound chip array index
+ * @cpcm_idx - capture PCM index array associated with USB device
+ * @ppcm_idx - playback PCM index array associated with USB device
+ * @num_capture - number of capture streams
+ * @num_playback - number of playback streams
+ * @list - list head for SoC USB devices
+ **/
+struct snd_soc_usb_device {
+	int card_idx;
+	int chip_idx;
+
+	/* PCM index arrays */
+	unsigned int *cpcm_idx; /* TODO: capture path is not tested yet */
+	unsigned int *ppcm_idx;
+	int num_capture; /* TODO: capture path is not tested yet */
+	int num_playback;
+
+	struct list_head list;
+};
+
+/**
+ * struct snd_soc_usb
+ * @list - list head for SND SOC struct list
+ * @component - reference to ASoC component
+ * @connection_status_cb - callback to notify connection events
+ * @priv_data - driver data
+ **/
+struct snd_soc_usb {
+	struct list_head list;
+	struct snd_soc_component *component;
+	int (*connection_status_cb)(struct snd_soc_usb *usb,
+				    struct snd_soc_usb_device *sdev,
+				    bool connected);
+	void *priv_data;
+};
+
+#if IS_ENABLED(CONFIG_SND_SOC_USB)
+int snd_soc_usb_connect(struct device *usbdev, struct snd_soc_usb_device *sdev);
+int snd_soc_usb_disconnect(struct device *usbdev, struct snd_soc_usb_device *sdev);
+void *snd_soc_usb_find_priv_data(struct device *usbdev);
+
+struct snd_soc_usb *snd_soc_usb_allocate_port(struct snd_soc_component *component,
+					      void *data);
+void snd_soc_usb_free_port(struct snd_soc_usb *usb);
+void snd_soc_usb_add_port(struct snd_soc_usb *usb);
+void snd_soc_usb_remove_port(struct snd_soc_usb *usb);
+#else
+static inline int snd_soc_usb_connect(struct device *usbdev,
+				      struct snd_soc_usb_device *sdev)
+{
+	return -ENODEV;
+}
+
+static inline int snd_soc_usb_disconnect(struct device *usbdev,
+					 struct snd_soc_usb_device *sdev)
+{
+	return -EINVAL;
+}
+
+static inline void *snd_soc_usb_find_priv_data(struct device *usbdev)
+{
+	return NULL;
+}
+
+static inline struct snd_soc_usb *
+snd_soc_usb_allocate_port(struct snd_soc_component *component, void *data)
+{
+	return ERR_PTR(-ENOMEM);
+}
+
+static inline void snd_soc_usb_free_port(struct snd_soc_usb *usb)
+{ }
+
+static inline void snd_soc_usb_add_port(struct snd_soc_usb *usb)
+{
+	return -EINVAL;
+}
+
+static inline void snd_soc_usb_remove_port(struct snd_soc_usb *usb)
+{
+	return -ENODEV;
+}
+#endif /* IS_ENABLED(CONFIG_SND_SOC_USB) */
+#endif /*__LINUX_SND_SOC_USB_H */
diff --git a/sound/soc/Kconfig b/sound/soc/Kconfig
index a52afb423b46..c993705c8ac2 100644
--- a/sound/soc/Kconfig
+++ b/sound/soc/Kconfig
@@ -84,6 +84,16 @@  config SND_SOC_UTILS_KUNIT_TEST
 config SND_SOC_ACPI
 	tristate
 
+config SND_SOC_USB
+	tristate "SoC based USB audio offloading"
+	depends on SND_USB_AUDIO
+	help
+	  Enable this option if an ASoC platform card has support to handle
+	  USB audio offloading.  This enables the SoC USB layer, which will
+	  notifies the ASoC USB DPCM backend DAI link about available USB audio
+	  devices.  Based on the notifications, sequences to enable the audio
+	  stream can be taken based on the design.
+
 # All the supported SoCs
 source "sound/soc/adi/Kconfig"
 source "sound/soc/amd/Kconfig"
diff --git a/sound/soc/Makefile b/sound/soc/Makefile
index fd61847dd1eb..adf9d9203778 100644
--- a/sound/soc/Makefile
+++ b/sound/soc/Makefile
@@ -35,6 +35,8 @@  endif
 
 obj-$(CONFIG_SND_SOC_ACPI) += snd-soc-acpi.o
 
+obj-$(CONFIG_SND_SOC_USB) += soc-usb.o
+
 obj-$(CONFIG_SND_SOC)	+= snd-soc-core.o
 obj-$(CONFIG_SND_SOC)	+= codecs/
 obj-$(CONFIG_SND_SOC)	+= generic/
diff --git a/sound/soc/soc-usb.c b/sound/soc/soc-usb.c
new file mode 100644
index 000000000000..bd2d68164206
--- /dev/null
+++ b/sound/soc/soc-usb.c
@@ -0,0 +1,218 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2022-2024 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+#include <linux/of.h>
+#include <linux/usb.h>
+#include <sound/soc-usb.h>
+#include "../usb/card.h"
+
+static DEFINE_MUTEX(ctx_mutex);
+static LIST_HEAD(usb_ctx_list);
+
+static struct device_node *snd_soc_find_phandle(struct device *dev)
+{
+	struct device_node *node;
+
+	node = of_parse_phandle(dev->of_node, "usb-soc-be", 0);
+	if (!node)
+		return ERR_PTR(-ENODEV);
+
+	return node;
+}
+
+static struct snd_soc_usb *snd_soc_usb_ctx_lookup(struct device_node *node)
+{
+	struct snd_soc_usb *ctx;
+
+	if (!node)
+		return NULL;
+
+	mutex_lock(&ctx_mutex);
+	list_for_each_entry(ctx, &usb_ctx_list, list) {
+		if (ctx->component->dev->of_node == node) {
+			mutex_unlock(&ctx_mutex);
+			return ctx;
+		}
+	}
+	mutex_unlock(&ctx_mutex);
+
+	return NULL;
+}
+
+static struct snd_soc_usb *snd_soc_find_usb_ctx(struct device *dev)
+{
+	struct snd_soc_usb *ctx;
+	struct device_node *node;
+
+	node = snd_soc_find_phandle(dev);
+	if (!IS_ERR(node)) {
+		ctx = snd_soc_usb_ctx_lookup(node);
+		of_node_put(node);
+	} else {
+		ctx = snd_soc_usb_ctx_lookup(dev->of_node);
+	}
+
+	return ctx ? ctx : NULL;
+}
+
+/**
+ * snd_soc_usb_find_priv_data() - Retrieve private data stored
+ * @usbdev: device reference
+ *
+ * Fetch the private data stored in the USB SND SOC structure.
+ *
+ */
+void *snd_soc_usb_find_priv_data(struct device *usbdev)
+{
+	struct snd_soc_usb *ctx;
+
+	ctx = snd_soc_find_usb_ctx(usbdev);
+
+	return ctx ? ctx->priv_data : NULL;
+}
+EXPORT_SYMBOL_GPL(snd_soc_usb_find_priv_data);
+
+/**
+ * snd_soc_usb_allocate_port() - allocate a SOC USB port for offloading support
+ * @component: USB DPCM backend DAI component
+ * @num_streams: number of offloading sessions supported
+ * @data: private data
+ *
+ * Allocate and initialize a SOC USB port.  The SOC USB port is used to communicate
+ * different USB audio devices attached, in order to start audio offloading handled
+ * by an ASoC entity.  USB device plug in/out events are signaled with a
+ * notification, but don't directly impact the memory allocated for the SOC USB
+ * port.
+ *
+ */
+struct snd_soc_usb *snd_soc_usb_allocate_port(struct snd_soc_component *component,
+					      void *data)
+{
+	struct snd_soc_usb *usb;
+
+	usb = kzalloc(sizeof(*usb), GFP_KERNEL);
+	if (!usb)
+		return ERR_PTR(-ENOMEM);
+
+	usb->component = component;
+	usb->priv_data = data;
+
+	return usb;
+}
+EXPORT_SYMBOL_GPL(snd_soc_usb_allocate_port);
+
+/**
+ * snd_soc_usb_free_port() - free a SOC USB port used for offloading support
+ * @usb: allocated SOC USB port
+
+ * Free and remove the SOC USB port from the available list of ports.  This will
+ * ensure that the communication between USB SND and ASoC is halted.
+ *
+ */
+void snd_soc_usb_free_port(struct snd_soc_usb *usb)
+{
+	snd_soc_usb_remove_port(usb);
+	kfree(usb);
+}
+EXPORT_SYMBOL_GPL(snd_soc_usb_free_port);
+
+/**
+ * snd_soc_usb_add_port() - Add a USB backend port
+ * @usb: soc usb port to add
+ *
+ * Register a USB backend DAI link to the USB SOC framework.  Memory is allocated
+ * as part of the USB backend DAI link.
+ *
+ */
+void snd_soc_usb_add_port(struct snd_soc_usb *usb)
+{
+	mutex_lock(&ctx_mutex);
+	list_add_tail(&usb->list, &usb_ctx_list);
+	mutex_unlock(&ctx_mutex);
+}
+EXPORT_SYMBOL_GPL(snd_soc_usb_add_port);
+
+/**
+ * snd_soc_usb_remove_port() - Remove a USB backend port
+ * @usb: soc usb port to remove
+ *
+ * Remove a USB backend DAI link from USB SOC.  Memory is freed when USB backend
+ * DAI is removed, or when snd_soc_usb_free_port() is called.
+ *
+ */
+void snd_soc_usb_remove_port(struct snd_soc_usb *usb)
+{
+	struct snd_soc_usb *ctx, *tmp;
+
+	mutex_lock(&ctx_mutex);
+	list_for_each_entry_safe(ctx, tmp, &usb_ctx_list, list) {
+		if (ctx == usb) {
+			list_del(&ctx->list);
+			break;
+		}
+	}
+	mutex_unlock(&ctx_mutex);
+}
+EXPORT_SYMBOL_GPL(snd_soc_usb_remove_port);
+
+/**
+ * snd_soc_usb_connect() - Notification of USB device connection
+ * @usbdev: USB bus device
+ * @sdev: USB SND device to add
+ *
+ * Notify of a new USB SND device connection.  The sdev->card_idx can be used to
+ * handle how the DPCM backend selects, which device to enable USB offloading
+ * on.
+ *
+ */
+int snd_soc_usb_connect(struct device *usbdev, struct snd_soc_usb_device *sdev)
+{
+	struct snd_soc_usb *ctx;
+
+	if (!usbdev)
+		return -ENODEV;
+
+	ctx = snd_soc_find_usb_ctx(usbdev);
+	if (IS_ERR(ctx))
+		return -ENODEV;
+
+	mutex_lock(&ctx_mutex);
+	if (ctx->connection_status_cb)
+		ctx->connection_status_cb(ctx, sdev, true);
+	mutex_unlock(&ctx_mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(snd_soc_usb_connect);
+
+/**
+ * snd_soc_usb_disconnect() - Notification of USB device disconnection
+ * @usbdev: USB bus device
+ * @sdev: USB SND device to remove
+ *
+ * Notify of a new USB SND device disconnection to the USB backend.
+ *
+ */
+int snd_soc_usb_disconnect(struct device *usbdev, struct snd_soc_usb_device *sdev)
+{
+	struct snd_soc_usb *ctx;
+
+	if (!usbdev)
+		return -ENODEV;
+
+	ctx = snd_soc_find_usb_ctx(usbdev);
+	if (IS_ERR(ctx))
+		return -ENODEV;
+
+	mutex_lock(&ctx_mutex);
+	if (ctx->connection_status_cb)
+		ctx->connection_status_cb(ctx, sdev, false);
+	mutex_unlock(&ctx_mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(snd_soc_usb_disconnect);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("SoC USB driver for offloading");